EP3026386A1

EP3026386A1 - Plate heat exchanger and method of manufacture

Info

Publication number: EP3026386A1
Application number: EP15171106.6A
Authority: EP
Inventors: Charles Penny; Ware Adrian
Original assignee: Senior UK Ltd
Current assignee: Senior UK Ltd
Priority date: 2014-06-13
Filing date: 2015-06-09
Publication date: 2016-06-01
Anticipated expiration: 2035-06-09
Also published as: EP3026386B1

Abstract

A method of manufacture of a heat exchanger comprising a plurality of heat exchange plates, said method comprises:
individually forming a plurality of heat exchange cells, each comprising a respective first and second plate member, by joining said first and second plates together with a first joint extending around a perimeter of said first and second plates, and one or more second joints located within said perimeter;
individually testing each said cell to check for fluid leaks;
joining said plurality of individual heat exchange cells together by placing said plurality of cells into an assembly of cells;
forming an outer joint around said plurality of cell perimeters;
forming an inlet joint joining together a plurality of inlets of said cells, and
forming an outlet joint by joining together a plurality of outlets of said plurality of cells.

Description

Field of the Invention

The present invention relates to a heat exchanger, and particularly, although not exclusively to an exhaust gas recirculation heat exchanger.

Background of the Invention

Heat exchangers that cool hot gases with a coolant liquid stream (and as a specific example an Exhaust Gas Recirculation Cooler) have a number of requirements that drive continuing design developments, including the following:

1. Customers' packaging space is being reduced.
2. Greater heat exchange and lower pressure drops are being specified which either requires a larger heat exchanger of traditional design or a new design.
3. Customers are continuously looking to reduce both weight and cost.
4. The delivery pressure of both fluids is increasing.
5. For different power ranges of the same engine, the customer specifies different mass flow rates. To maintain performance this would require a change in the cooler design. However, the customer wishes to restrict the cost of tooling.
6. Regeneration of the fouling caused by the exhaust gas back towards the clean condition is critical to maintaining high levels of performance.

On top of these drivers there are the ongoing needs:

1. To ensure that the thermal loading of the heat exchanger, especially at the gas inlet interface, is kept within safe limits. A major contributor to this is to control, reduce and stop boiling of the liquid coolant.
2. To have well distributed gas flows over the width of the plate.
3. To have good and well controlled flow of the coolant, especially at the gas inlet interface.
4. To ensure that the liquid side of the cooler does not have pockets that could trap air.
5. To have a design which allows both fluid interfaces to be either in line with the cooler or at right angles to the cooler.

To aid manufacturability and thus help reduce costs.

1. As many internal joints that are designed to be leak tight to be checked prior to full assembly. This reduces the cost of scrap.
2. As many internal joints that are designed to carry a load can be tested prior to full assembly. This reduces the cost of scrap.
3. All joints that can not be checked as sub-assemblies to be re-workable in the full assembly.

Exhaust gas recirculation heat exchangers are used in vehicles to remove heat from the recirculated exhaust of an internal combustion engine. Exhaust gas recirculation is a nitrogen oxide NOx reduction technique used in petrol/gasoline or diesel engines. EGR works by which circulating a portion of the engine's exhaust gases back to the cylinders of the engine which reduces the percentage of oxygen and so reduces the flame temperature of the fuel inside the engine which reduces NOx formation. The cooler the recirculated gas the more gas can be flowed and the lower the flame temperature.
In modern diesel engines, the recirculated exhaust gas is cooled using a heat exchanger to allow a greater mass of gas to be recirculated into the cylinders of the engine than if the recirculated gas is uncooled.
Typically a heat exchanger for EGR use has a plurality of plates within a casing. Exhaust gases are passed through the plates, and the casing provides a fluid tight jacket around the plates to cool the gases in the plates.
Prior art heat exchangers for other uses comprise a series of a plurality of plates built as a stack and brazed together. This has an advantage that there is no outer casing, which reduces manufacturing cost. The braze holds the individual plate members together, and seals an outer wall around the plates.
Figure 1 herein shows a prior art heat exchanger of the brazed type. This prior art type of cooler is typically used as an oil cooler in the automotive industry, or in the dairy industry, and are generally used for liquid to liquid heat exchange where there is a relatively constant pressure on either side of the component. Typically such heat exchangers are used where the temperatures are not excessively high.
A problem with the prior art low temperature heat exchanger is that it requires a lot of brazing. The heat exchanger is built up as a series of individual flat metal plates, each of which are coated with a braze material. The plates are stacked up on top of each other, and the heat exchanger plates are brazed together as one assembly in a single operation.
A problem with the brazed joint is that one cannot be certain that the joints are correctly formed, or that there is any joint there at all. The only place where the braze is visible and accessible for testing is around the outer edges of the device, and around the inlet and outlet for the coolant. The whole assembly can be leak checked to see if there is any liquid leaking from the completed heat exchanger. However, the brazed joints inside the assembly are not accessible for inspection. Unless the device is pressure tested to failure, then it is not certain that all the internal brazed joints are correctly formed and are not leaking internally. The internal brazed joints cannot be tested nondestructively or inspected to make sure that they have the required strength to withstand the pressure pulsations to which the heat exchanger will be subjected to in use.
In an EGR application, the temperatures of the exhaust gases is higher. To withstand the cyclic pressures which the device is subjected to in use, it needs to be ensured that each one of the internal brazes joins properly to give mechanical strength between the plates. This is very difficult to ensure.
A further problem with the prior art when used for an application such as an EGR cooler is that the cooler does not flow the gas in its optimal flow.
A second objective in an EGR heat exchanger is to obtain heat transfer between two fluid flows as efficiently as possible.
In a known liquid to gas heat exchanger there are heat exchange plates which have gas running through a plurality of channels through the centres of the heat exchange plates, and liquid coolant surrounding the outside of the plates.
In the known liquid to gas heat exchangers, a flat area between the inlet and outlet tubes does not act as a fin because the whole of the surface is driven to the coolant temperature.
In EP1159574 there is disclosed a plate heat exchanger for use in the food industry, for cooling beverages such as beer, which comprises a plurality of a corrugated plates, where pairs of adjacent plates are coated with a solder material so that corrugated projections of each pair of plates are brazed together, and the plates are bent over at their edges, so that when the plates are stacked one on top of the other the edges of the plates can be brazed together to form a heat exchanger which does not need an outer casing.

Summary of the Invention

In a known liquid to gas heat exchanger, a flat area between the inlet and outlet tubes does not act as a fin because the whole of the surface is driven to the coolant temperature. However, the inventors herein have realised that if the gas and liquid flows were reversed, so that the coolant was on the inside of the plate and the gas was on the outside of the plate, the flat areas would become a fin and would operate to exchange heat between gas and liquid.
The known heat exchanger suffers from the problem that in the prior art seamless plate cooler, the welded section is a secondary surface, and the gas passage primary surface are both at coolant temperature. Therefore part of the heat exchange surface is wasted, and not used for efficient heat exchange.
Specific embodiment heat exchangers disclosed herein preferably have a primary heat exchange surface and a secondary heat exchange surface formed from a single sheet of material.
However with the present heat exchanger, those surfaces are not utilised for heat exchange.
In a specific method of construction disclosed herein, an individual cell is formed, so that two plates are joined together to form two sides of a cell, with either a weld or a braze extending all the way around a perimeter of the cell, and with individual welds or brazing across a central area of the cell.
Each individual cell is pressure tested or otherwise checked for fluid leaks and mechanical integrity, before assembly into a stack which forms the finished heat exchanger. A plurality of cells, each of which has been tested for fluid leaks and found to be fluid tight and have adequate mechanical integrity are joined together, and the only places of the cells which need to be joined together are the areas around the inlet and outlet interfaces of the cells, and around the outer perimeters of the cells, all of which can be tested via a final pressure leak test of the finished stack.
According to a first aspect, there is provided a gas to liquid coolant heat exchanger for transferring heat between a gas and a liquid coolant, said heat exchanger comprising:

a plurality of heat exchange cells;
each said cell comprising a liquid coolant inlet and the liquid coolant outlet;
each said cell comprising a pair of plates each said plate having a plurality of grooves which form a plurality of liquid coolant channels between said plates, extending between said liquid coolant inlet and liquid coolant outlet;
characterised in that
each said cell contains said liquid coolant within said cell between said pair of plates.

According to a second aspect, there is provided a heat exchange cell for a gas to liquid heat exchanger, said cell comprising:

a first plate and the second plate;
at least one of said plates having a plurality of grooves which form a plurality of liquid coolant channels between said plates,
characterised in that
each said cell contains said liquid coolant within said cell between said plates.

According to a third aspect, there is provided a gas to liquid heat exchanger comprising:

a plurality of heat exchange cells, each said cell comprising a first plate and a second plate;
wherein each said heat exchange cell comprises a liquid inlet aperture and a liquid outlet aperture;
each said plate comprising a sealed perimeter of the coolant channels, and a plurality of internal fluid channels;
each heat exchange cell having its coolant perimeter sealed independently of the outer perimeter of each other said heat exchange cell;
said plurality of heat exchange cells arranged side-by-side in a stack arrangement;
wherein said plurality of heat exchange cells are sealed to each other by an outer perimeter seal around at least part of their respective outer perimeters, to form a plurality of gas channels extending between said plurality of cells.

According to a fourth aspect, there is provided a method of manufacture of a heat exchanger comprising a plurality of heat exchange cells, said method comprising:

individually forming each of said plurality of heat exchange cells, each comprising a respective first plate and a second plate, by joining said first and second plates together with a continuous joint extending around the coolant perimeter of said second plate to form a cavity between said second plate said first plate, through which a liquid coolant may flow;
individually testing each said cell to check for fluid leaks in said cavity;
joining said plurality of individual heat exchange cells together by placing said plurality of cells into an assembly of cells;
forming an outer joint around said plurality of cell perimeters;
forming an inlet joint joining together a plurality of inlets of said cells, and
forming an outlet joint by joining together a plurality of outlets of said plurality of cells.

According to a fifth aspect, there is provided a heat exchange cell for a gas to liquid heat exchanger, said cell comprising:

a first plate and a second plate;
at least one of said first and second plates comprising a plurality of elongate grooves, said plurality of grooves forming a plurality of liquid coolant channels inside said cell;
at least one of said first and/or second plates having a plurality of outwardly projecting studs, which project in a direction outwardly from a plane which intersects an outer surface of a said plate at the position of said plurality of grooves.

According to a sixth aspect there is provided a gas to liquid heat exchanger comprising a plurality of heat exchange cells,
each said cell comprising an inner plate and an outer plate;
said plurality of heat exchange cells being stacked together side-by-side to form a plurality of gas passages there between;
each said cell having an outer surface comprising a plurality of projections which extend into said gas passages between said cells, for promoting turbulent gas flow between said cells.
Individual embodiments may provide a stack of substantially parallel plates;
each plate having a plurality of corrugations, which form channels when placed against an adjacent plate;
the edges of the plates being folded over to form a wall or rim, so that the edge of one plate lies adjacent and substantially parallel to the edge of an adjacent parallel plate;
pairs of plates are joined together around their inner coolant periphery, and between channels in the central region of the plates;
a plurality of cells, each formed from a pair of adjacent plates (or one plate bent over on itself) are brazed together around their outer edges, and at their inlet and outlet ports.
The heat exchanger may be fabricated by:

forming a heat exchange cell from two parallel plates, or a single plate bent over, which has a plurality of corrugations so that the two plates form channels there between;
laser welding around a coolant periphery of at least one said plate;
each cell having an inlet port and outlet port;
each cell having a peripheral rim or skirt which is folded over so that when adjacent cells are placed next to each other the rims contact each other and part of one rim lies substantially parallel to part of an adjacent room of an adjacent cell;
stacking a plurality of cells together; and
brazing around the outer rims of the cells to form an outer seal, so that the spaces between adjacent cells form channels for a first fluid path, whilst the interior of each cell forms a channel for a second fluid;
the brazing operation also connects adjacent cells together at the inlet port and the outlet ports, thereby sealing the first fluid path between aid adjacent cells, and a second fluid path inside the cells; and
pressure testing the whole assembly after brazing.

Hence, each individual cell is pressure tested individually, and any faulty cells can be rejected or recycled before they are incorporated into an assembly of cells, thereby improving the reliability of the finished heat exchanger, since only cells which have passed their individual pressure test are included in the stack of cells from which the finished heat exchanger is constructed.
Further, by joining each cell individually prior to assembly into a stack, the joints between individual channels in each cell are formed more reliably than in the prior art case, where joints between individual channels are formed in a brazing operation where the brazes cannot be individually nondestructively tested, and can only be checked by cutting open and sacrificing a finished heat exchanger to check the internal brazes. Hence embodiments of the present invention can be tested nondestructively by pressure testing of each cell individually before assembly into the plate heat exchanger, and by testing the whole plate exchanger after final assembly of the cells.
Preferably there is provided a gas to liquid heat exchanger that encloses a liquid coolant within a cell.
Preferably each cell is designed to control and direct the flow of coolant such that there is adequate flow of coolant across the gas inlet interface to reduce and/or eliminate the occurrence of coolant boiling.
Preferably a said cell is designed to control and direct the flow of coolant such that there is adequate flow of coolant in all of a plurality of longitudinal coolant channels, so as to reduce and/or eliminate the occurrence of coolant boiling.
Preferably said cell is designed to significantly reduce the volume of coolant within the heat exchanger such that the cooler is both smaller and lighter in its wet condition compared to prior art coolers of similar heat exchange capacity.
Said heat exchanger may effectively 'decouple' the geometry of the coolant side and the gas side of a heat exchanger such that the coolant performance and the gas performance can be maximised.
Preferably, said heat exchanger has a heat exchange of > 0.25 W/m².K.kg at 98% effective or greater when the pressure loss times absolute inlet pressure of the gas is <0.5 bar.bar in the range of K (gas inlet temperature - coolant inlet temperature) of 200°C to 500°C.
Preferably, in a main part of the heat exchanger, both fluids flow in paths which extend along a substantially longitudinal direction of said heat exchanger.
Preferably, said heat exchanger has no separate outer case, bulkhead or separate gas header.
Preferably, said heat exchanger can interface the gas inlet and outlet either longitudinally or perpendicularly to the cooler, or a combination of one of the gas inlet or outlet interfacing longitudinally to the main length of the heat exchanger, and the other of the inlet or outlet interfacing perpendicularly to the main length of the heat exchanger.
Preferably said heat exchanger has the coolant entry within the main path of the gas flow characterised by the coolant still being able to vent any gas within the coolant void.
The heat exchanger may have the coolant entry outside the main path of the gas flow, characterised by the coolant still being able to vent any gas within the coolant void.
In the embodiments described herein, each individual cell fully contains liquid coolant within the cell.
In the embodiments described herein, there is shown a method of manufacture of a heat exchanger, whereby two plates making up a heat exchange cell are welded together and tested for leaks before assembly of the cells into a stack/core comprising a full heat exchanger assembly.
In the embodiments described herein, there are disclosed a plurality of Protrusions or studs which project into the gas passages between the cells, which introduce turbulence into the gas flow, but without significantly affecting the flow characteristics or the volume of the liquid coolant.
Other aspects are as set out in the claims herein.

Brief Description of the Drawings

For a better understanding of the invention and to show how the same may be carried into effect, there will now be described by way of example only, specific embodiments, methods and processes according to the present invention with reference to the accompanying drawings in which:

Figure 1 shows a prior art heat exchanger which is fabricated in a single brazing operation;
Figure 2 herein shows in perspective view from one side a first heat exchanger according to a specific embodiment herein;
Figure 3 herein shows the first heat exchanger in view from one side;
Figure 4 herein shows the first heat exchanger of figures 2 and 3 in cutaway view along a line A - A' in figure 3;
Figure 5 herein shows the first heat exchanger of figures 2 and 3 in cutaway view along a line B - B' in figure 3;
Figure 6 herein shows the first heat exchanger of figures 2 and 3in cutaway view along the line C - C' in figure 3;
Figure 7 herein shows the first heat exchanger of figures 2 and 3 in cutaway view along the line D - D' in figure 3;
Figure 8 herein shows the first heat exchanger of figures 2 and 3 herein in cutaway view along the line E - E' in figure 3;
Figure 9 herein shows a second heat exchanger according to a second specific embodiment in perspective view form a first side, a first end and above;
Figure 10 herein shows the second heat exchanger according to a second specific embodiment in perspective view from a first side;
Figure 11 herein shows a core of the second heat exchanger in view from the first side;
Figure 12 herein shows the second heat exchanger in perspective view from the first side, a first end and above;
Figure 13 herein shows the second heat exchanger in perspective view from a second side, a first end, and above;
Figure 14 herein shows a core of the second heat exchanger in perspective view from the second side, the first end, and above;
Figure 15 herein shows the core of the second heat exchanger in perspective view from the first side, the first end and above;
Figure 16 herein, shows a first cell of the second heat exchanger, being a cell located on a side of the core;
Figure 17 herein shows a second cell of the heat exchanger, being a cell located within the core;
Figure 18 herein shows in perspective view from a first side, a first end and both a first side plate of the second heat exchanger;
Figure 19 herein shows in perspective view from the second side, a first end, and above a second side plate of the second heat exchanger;
Figure 20 herein shows a section across the line A-A' in figure 10 herein, showing an internal structure of the second heat exchanger;
Figure 21 herein shows a section across the line B-B' in figure 10 herein, showing an internal structure of the second heat exchanger at the ends of the second plates therein;
Figure 22 herein shows a section across the line C-C' in figure 10 herein showing an internal structure of the second heat exchanger;
Figure 23 herein shows a section across the line D-D' in figure 10 herein, showing an internal structure of the second heat exchanger along the length of the heat exchange cells;
Figure 24 herein shows a section across the line E-E' in figure 10, showing an internal structure of the second heat exchanger;
Figure 25 herein shows a velocity contour gas flowing in a middle plane, at gas channel 7, within the second heat exchanger as gas flows from the gas inlet to the gas outlet between adjacent cells;
Figure 26 shows a velocity vector plot of gas flowing in gas channel 1, in a middle plane view, from the gas inlet end towards the centre of the second heat exchanger;
Figure 27 shows a velocity vector plot of gas flowing in gas channel 1, in a middle plane view, from the centre of the second heat exchanger towards the second end, where gas is outlet from the second heat exchanger;
Figure 28 shows a velocity vector plot at a second end of heat exchanger, viewed in a direction perpendicular to the main planes of the heat exchange cells, showing exhaust of gas through the outlet passage;
Figure 29 herein shows a velocity magnitude plot of gas flowing through the second heat exchanger between a gas inlet and a gas outlet in three-dimensional view; and
Figure 30 shows a velocity vector plot of coolant flowing through a cell at the middle plane of the cell from a coolant inlet at the second end of the second heat exchanger, towards a coolant outlet at a first end of the second heat exchanger, and showing mass flow fraction as a % for individual coolant channels 1 -13 across a depth of the heat exchange cell.

Detailed Description of the Embodiments

There will now be described by way of example a specific mode contemplated by the inventors. In the following description numerous specific details are set forth in order to provide a thorough understanding. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well known methods and structures have not been described in detail so as not to unnecessarily obscure the description.
Referring to figure 2 herein, there is illustrated schematically in perspective view from above and the front, a plate heat exchanger according to a specific embodiment disclosed herein.
The plate heat exchanger 200 comprises a plurality of heat exchange cells 201; a first fluid inlet tube 203; a first fluid outlet tube 204; a second fluid inlet tube 205; and a second fluid outlet tube 206. The first inlet tube 203 and first outlet tube 204 are positioned on a same front face 202 of the heat exchanger. The second fluid inlet tube 205 and the second fluid outlet tube 206 are positioned on opposite outer faces of the heat exchanger, the second fluid inlet tube 205 being positioned on the front face 209, and the second fluid outlet tube 206 being positioned on the rear face of the heat exchanger. The first fluid inlet tube 203 and first fluid outlet tube 204 form a first fluid path through the heat exchanger for carrying coolant, such as a liquid coolant. The second fluid inlet tube 205 and the second fluid outlet tube 206 form a second fluid path through the heat exchanger for the second fluid, being an internal combustion engine exhaust gas to be cooled prior to being mixed with an inlet air to the engine.
The plate heat exchanger comprises a plurality of substantially identical cells, each cell constructed from a pair of plates. The plurality of cells are positioned side by side to form a stack of said cells. The outer most cells are slightly different to the inner cells such that the void for the gas inlet and outlet is closed and there are interfaces for the coolant inlet and outlet and the gas inlet and outlet if flowed perpendicular to the main cooler. The first and second outermost cells are slightly different to each other, because the first outer cell has a pair of apertures positioned for location of the first inlet tube 203 and the first outlet tube 204, whereas the second outer most plate does not have such apertures.
Outside of the outer cells a protective plate may be used. This gives strength to the fluid inlet and outlet interfaces, adds stiffness to the outer skin of the cooler for clamping and may cover the heat exchange section of the cooler to give a lower surface temperature.
The heat exchanger may be attached to a surface, for example a vehicle engine block by a pair of brackets 206, 207 respectively which extend around a main body of the plate heat exchanger, and which has a plurality of tabs having apertures through which bolts or other fixing means can be passed to attach the brackets to a surface. Alternatively the heat exchanger may be attached to a surface by the outer protective plates if used.
In the heat exchanger of figure 2, at the position at which the gas is inlet and outlet from the heat exchanger, there is an uncooled section which allows the gas to spread out across the whole of the face of the cell at the coolant perimeter.
Referring to figure 3 herein, there is illustrated in view from the front, the heat exchanger of figure 2 herein. As viewed from the front, the heat exchanger has a substantially rectangular shape with rounded corners, with the first fluid inlet tube 203 and the first fluid outlet tube 204 being located adjacent a same first side 303 of the rectangle, and inwardly from a respective first end 300 and second end 301. The second fluid outlet tube 206 is located adjacent the first end 300 and adjacent the same side as the first fluid inlet tube 203 and the first fluid outlet tube 204, whilst the second fluid inlet tube 205 is located adjacent the second end 301, and adjacent an opposite second side 304, the second fluid inlet 205 and second fluid outlet 206 being mounted on opposite faces of the heat exchanger to each other. The first end 300 and the second end 301 up to the welded joint of the cell 305 and 305 forms a void where the second fluid can distribute and flow over the full width of the cell.
Referring to figure 4 herein, there is shown in cutaway view along the section A - A', the heat exchanger of figure 2 herein. The main body of the heat exchanger is constructed from a plurality of cells 400 - 409, stacked side-by-side. Each cell is substantially identical to each other cell, within manufacturing tolerances in the heat exchange section. Each cell comprises a first plate and a second plate.
Each first plate comprises a substantially flat sheet having a first (inner facing) face facing inside the cell, and a first (outer facing) face facing outside the cell, each said first inner facing face extending in a respective first inner plane and each said first outer facing face extending in a first outer plane, there being a plurality of first ridges in the sheet, wherein outer extremities of the first ridges lie in a first ridge plane, said first ridge plane extending substantially parallel to said first inner plane and first outer plane. An outer rim portion of said first plate is formed into a skirt portion which extends around an outer perimeter of said first plate, to form a substantially frusto pyramid shaped skirt having skirt walls which extend in planes transverse to the first inner plane, first outer plane and the ridge plane.
Each second plate comprises a substantially flat sheet having a second (inner facing) face, facing inside the cell, and a second (outer facing) face facing outside the cell, each said second inner facing face extending in a respective second inner plane, and each said second outer facing face extending in a second outer plane, there being a plurality of ridges in the sheet, wherein outer extremities of the second set of ridges lie in a second ridge plane, said second inner plane, second outer plane and second ridge plane extending parallel to each other, and parallel to the first inner plane, first outer plane and first ridge plane. Like the first plate, the second plate does have a peripheral skirt portion.
The first and second plates are joined together such that the plurality of ridges of the first plate lie opposite the plurality of ridges of the second plate, so that between the first and second plates there are formed one or a plurality of internal cell channels 419 - 431 defined by the ridges.
The one or a plurality of internal cell channels of the first cell and the one or plurality of internal cell channels of one or more adjacent cells in the stack collectively form a first fluid channel through the heat exchanger, for carrying the first fluid. In the best mode embodiment, the plurality of internal cell channels of each cell extend in a direction along a length of the heat exchanger between the first fluid inlet aperture and the first fluid outlet aperture of said cell.
Between adjacent cells, where a second cell is stacked on top of or adjacent a first cell, a space between a second (upper) plate of the first cell and a first (lower) plate of the second cell forms a second plurality of fluid channels, 432 - 444 which extend between the second fluid inlet apertures and the second fluid outlet apertures of the cells. Preferably, the second fluid channels also extend in a direction along a length of the heat exchanger.
In use, a first fluid passing through the first fluid channels 419 - 431 travels in a first direction along a length of the heat exchanger, whilst a second fluid passing through the second fluid channels 432 - 444 travels in a second direction along a length of the heat exchanger, where the first and second directions are generally opposite to each other, and thereby achieving a contraflow of the fluids within the heat exchanger.
This means that a hot exhaust gas passing through the second fluid inlet apertures and travelling externally outside the cells transfers heat through the plate walls to a second fluid (coolant fluid) which is about to exit the heat exchanger through the first fluid outlet aperture. Similarly, the first fluid (coolant) at its coolest point on entering the heat exchanger draws heat through the plate walls from the exhaust gas which is about to leave the heat exchanger through the second fluid outlet, and which has already experienced a degree of cooling during its passage through the heat exchanger, to cool the exhaust gas at its coolest point as it leaves the heat exchanger. The coolant acquires heat during its passage through the heat exchanger, whereas the exhaust gas loses heat during its passage through the heat exchanger.

Individual Cell Construction

Each plate is constructed from a single sheet of metal, which is stamped out. Pairs of plates, each having a set of ridges, and a respective plate inlet aperture and plate outlet aperture, and forming for skirt portion which extends around the first plate.
The first and second plates are welded to each other, preferably using a laser welding machine, introducing a series of welds between the adjacent channels formed by the opposite ridges on the first and second plates, and by laser welding around a coolant perimeter region of the plates so that the set of first channels 419 - 431 are sealed and fluid tight from channels 432 - 444. Further the laser weld joins each pair of plates either side of first channels 419 - 431 such that the cell is able to constrain the internal pressure of fluid 1.

Stack Construction

As shown in figure 4, the stack of cells is constructed by laying one cell on top of the other, so that the plurality of cells lie side-by-side. Between pairs of adjacent cells, there is created a void, so that a plurality of voids 410 - 418 are created between the cells, which in totality form a second fluid passage through the heat exchanger, between the second fluid inlet and the second fluid outlet.
Referring to figure 5 herein, there is shown in cutaway view along the section B - B', the heat exchanger of figures 2 and 3 herein. In figure 5 the outwardly projecting studs in the plates are shown sectioned, and the bracket is not shown. These studs cause turbulence of the gas. Some of the studs may be used to space one cell from another adjacent cell.
Referring to figure 6 herein, there is shown in cutaway view along the section C - C', the heat exchanger of figures 2 and 3 herein. There is shown the first fluid inlet 203 in cross-sectional view. The first fluid inlet 203 comprises a tubular cylindrical portion 600 which is a fixed around a perimeter of an inlet aperture of an outermost facing plate 208. The tubular cylindrical portion is a fixed to the region around the aperture by brazing or soldering. A collection tube having one end which fits inside the cylindrical stub tube 600, is held in place by solder or brazing.
The plurality of perimeter regions 602 - 611 around the individual first inlet apertures of the individual cells are open, so that the first fluid can permeate into the first channels inside the individual cells.
Referring to figure 7 herein, there is shown in cutaway view along the section D - D', the heat exchanger of figures 2 and 3 herein. Shown in figure 7 is the second fluid outlet 206. The second fluid outlet comprises a cylindrical tube 700; a cylindrical stub ring or tube 701 which is soldered to an outermost facing perimeter region of a second inlet aperture of the plate on the rear face of the heat exchanger; and the collective plurality of second fluid outlet apertures of the individual cells.
Around their second outlet apertures, each individual cell has its first and second plates are laser welded together, so that fluid passing into the spaces between adjacent cells cannot leak into the inside of the cells themselves.
Referring to figure 8 herein, there is shown in cutaway view along the section E - E', the heat exchanger of figures 2 and 3 herein. Shown in figure 8 in cross-sectional view are the first fluid inlet 203 and the second fluid outlet 206, the second fluid outlet being of larger diameter than the first fluid inlet. The first fluid inlet comprises a cylindrical spigot, or tube 600, which is brazed or soldered to an outermost facing plate of the heat exchanger, and a substantially cylindrical outer tube 601 which is suitable for connecting to an external hose.
The second fluid outlet 206 comprises an annular spigot or tube 802, which is soldered or brazed to an outer surface of a plate at the rear of the heat exchanger around the second inlet apertures of the cells, and a tubular substantially cylindrical pipe 803 which can be connected into an exhaust gas circuit.
The first fluid inlet connects with a plurality of first fluid inlets of the individual cells, which collectively form a first fluid inlet passage 804 in the heat exchanger, and the second fluid outlet 206 forms a channel with a passage formed by the plurality of individual second fluid outlets, which collectively form a second fluid outlet channel 805 to allow the second fluid to pass from the channels between individual cells in the heat exchanger.

Overview of Method of Manufacture

An overall method of manufacture is as follows. Each individual cell is formed from a pair of plates.
Each pair of plates is joined around their coolant perimeter, and in a region within the outer perimeter. Joining can be either by brazing, or by laser welding.
Each cell is pressure tested to check for leaks and mechanical integrity around the cell perimeter, and in the region bounded by the coolant perimeter.
A plurality of cells are laid side-by-side and formed into a stack. The plurality of cells are joined together around the outer edges of the cells, and around the regions which border the inlet apertures and outlet apertures of the cells. Joining together of the cells to form the stack is by brazing or soldering.
The internal regions where adjacent cells are soldered or welded to each other inside the inlet passages and outlet passages can be inspected visually, and the joining around the outer perimeter of the cells can also be inspected visually.
Spigots are attached at the first inlet, second inlet, first outlet and second outlet.
The stack is then pressure tested by attaching tubes to the inlet and outlet spigots, and pressurising fluid through the first fluid channel and second fluid channel, and by measurement of the stack for leaks.

Cell Manufacture Method

Each plate is formed from a single sheet of metal material. A pair of plates is stamped out from a single sheet of metal material using a stamping machine. The stamping operation cuts a perimeter around a piece of initially flat metal material, and at the same time stamps a first plurality of ridges and troughs in a first area of the sheet of material to form a first plate, and a second plurality of ridges and troughs in a second area of material, to form a second plate.
An upper plate is positioned on top of a lower plate such that the plates lie parallel to each other and opposite each other side-by-side. The plurality of ridges and troughs on the respective first and second plates lie opposite each other, with ridges on the first plate lying opposite ridges on the second plate, and troughs on the first plate lying opposite troughs on the second plate, so that the adjacent opposite ridges can contact each other, and the adjacent opposite troughs between the ridges form a plurality of channels through the cell.
First and second plates are then joined together around a coolant perimeter, and along areas of the plates which contact each other, For example along regions between the channels. Joining can either be by welding, for example laser welding or brazing.
Once joined, each cell is individually tested for leaks and for robustness of the joints. Each cell can be visually inspected, or non-destructively pressure tested by injecting fluid under pressure into the cell and testing for leaks and excessive deformation, which may indicate weak welds or joins in the central area of the plates.

Stack Method of Manufacture

A plurality of cells, each of which has been previously leak tested, are assembled into a stack by laying the cells one on top of each other. The cells self - align with each other due to the skirt regions on each cell, which are angled in a substantially frusto pyramid shape which allows the cells to be stacked one on top of each other, with a lower outer surface of the first cell facing an upper outer surface of an adjacent second cell. The plurality of cells may be held together by clamping. The outwardly projecting studs may also set the spacing between cells.
The plurality of cells forming the stack are joined together in a single brazing or soldering operation. The plurality of skirt regions are joined, by brazing each skirt to one or more adjacent skirts.
Outer surfaces of the cells adjacent cell first fluid inlet passages are joined together by brazing or soldering, forming a plurality of circular or annular seals between adjacent cells. The plurality of adjacent seals around the first inlet's, and the circular first inlet apertures in the cells form the first inlet passage extending through the stack.
Similarly, the surface areas of adjacent cells which touch each other around the first fluid outlet passages are each sealed by welding or brazing to form a plurality of circular or annular seals, which together with the plurality of first outlet apertures form the first outlet passage extending through the stack.
Similarly, the outer perimeter edges of the cells are joined together by brazing or soldering, forming a plurality of perimeter seals between adjacent cells.
Having joined a plurality of cells together to form the stack, the completed stack may be visually inspected to make sure that there are no visually identifiable defects in the solders or brazes around the outer skirts, and in the regions around the first fluid inlet passage, first fluid outlet passage, second fluid inlet passage and second fluid outlet passage.
The first fluid inlet spigot, the first fluid outlet spigot, the second fluid inlet spigot, and the second fluid outlet spigot are located in the corresponding respective first fluid inlet aperture, first fluid outlet aperture, second fluid inlet aperture and second fluid outlet apertures, of the outermost plates on of the stack, and are joined to the material around those apertures by welding or brazing.
The completed stack with connected spigots may be pressure tested by connecting a fluid supply and drain tubes to form a first fluid circuit through the first inlet of the first outlet, and a second fluid circuit through the second inlet and second outlet and passing fluid through the first and second fluid channels. The stack can be pressure tested as a whole, with the first and second fluid channels being under pressure at the same time, or the first fluid channel can be pressure tested independently of the second fluid channel.
The heat exchanger disclosed herein is constructed of a series of cells which are joined together. Hence, rather than braze a series of plates together, as in the prior art heat exchanger, in the present heat exchanger there are individual cells, each of which can be checked for leaks before being joined together to make a complete heat exchanger.
The heat exchanger forms a cell from two plates, and encapsulates a liquid coolant within the cell. The primary and secondary heat exchange surfaces are formed from a single cell.
Gas flow occurs from one end of the plate to the other, across the full width of the face of the plate.
Coolant, via the channels in the cell, flows from near one end of the cell to near the other end, in an opposite direction to the other liquid, so there is contraflow between the cooling liquid and the liquid being called.
The cell has a sealed coolant channel across the gas inlet passage.
The heat exchanger does not have a bulkhead. Hence there is lower weight, bulk and cost, compared to the prior art exhaust gas recirculation heat exchanger. Specific embodiments disclosed herein may provide a heat exchanger without a bulkhead. The absence of a bulkhead lowers weight and reduced cost. It also avoids the problem of thermal loading at the bulkhead.
The heat exchanger does not need a separate case, because the casing is formed by the sides of the heat exchange plates themselves and the outermost plates.
The heat exchanger disclosed herein may provide a more compact EGR heat exchanger.
The heat exchanger disclosed herein may have a plate profile which is easier to manufacture than prior art plate profiles.
The individual cells may be laser welded, and hermetically sealed before being assembled into a full heat exchanger device.
The specific embodiments herein also have an advantage that there is no heat exchanger outer case, which reduces manufacturing cost, component weight and component bulk.
The heat exchanger herein forms gas inlet and outlet headers from the same plates which form the heat exchange surfaces. This reduces weight, bulk and cost.
A reduction in overall weight can being achieved, firstly because there is no thick wall casing, and secondly because there is significantly less coolant in the heat exchanger.
In the present embodiments, since the cells are hermetically sealed and are able to be leak tested as a single cell when sealed at the coolant inlet and outlet interfaces, this reduces the amount of rejects of full heat exchanger assemblies at the point of manufacture.
The heat exchangers disclosed herein have designed flexibility of the cell which allows some limited deformation under pressure and aids fouling regeneration.
In a conventional heat exchanger, there is a bulkhead and a reducer and an interface from the reducer so that heat exchange is not obtained straightaway right across the plates. In the embodiments herein, the plates themselves create a cavity which act as a reducer, thereby eliminating the need for a separate reducer section. There is created a cavity which acts as a reducer, within the cell itself.
The gas heat exchanger forms the gas inlet and outlet headers from the same plates as only used for heat exchange. The inlet and outlet ports are outboard of the main heat exchange area.
There is a cost saving in manufacture, because the only components used are a series of plates, and there are no other expensive components which do not actually aid heat exchange.
Although there is no outer casing, in the embodiment shown in figures 2 and 3, the reinforcement plate is added on the front and the back to surfaces of the heat exchanger.
Referring to figures 9 to 30 herein, there is illustrated a second heat exchanger according to a second specific embodiment. The second heat exchanger is designed for cooling a gas, using a liquid coolant.
Referring to figure 9 herein there is shown the second heat exchanger in perspective view from above , a first side and a first end;
Referring to figure 10 herein, there is illustrated schematically the second heat exchanger in view from a first side.
Referring to figure 11 herein, there is illustrated schematically the second heat exchanger in view from the first side, showing an outer most plate as transparent, so as to view a plurality of liquid coolant channels of an interior core part of the second heat exchanger, and outwardly protruding studs in the gas channels.
Referring to figure 12 herein, there is illustrated in perspective view from above and a first side, the second heat exchanger showing impartial cutaway view and interior of a central core of the heat exchanger.
Referring to figure 13 herein, there is illustrated in perspective view from above and a second side, the second heat exchanger showing impartial cutaway view and interior of a central core of the heat exchanger.
Referring to figures 14 and 15 herein, there is illustrated in perspective view from above and the second side, a central core of the second heat exchanger.
The second heat exchanger 900 comprises a plurality of heat exchange cells 901; a gas inlet manifold 902 cavity; a gas outlet tube 903; a liquid coolant inlet tube 904; a liquid coolant outlet tube 905, and an end flange 930. Each cell comprises a pair of heat exchange plates which are welded together, and a plurality of cells comprises a heat exchanger body. On the respective first and second outer sides of the heat exchanger body, there are two outer plates (shown as semi - transparent in figures 14 and 15) which protect the core of the heat exchanger body, and which provide a plurality of anchorage points for attaching the heat exchanger to a supporting component, for example an engine block or a vehicle bulkhead.
A main body of the heat exchanger comprises a plurality of individual plates which are stacked side-by-side to form the plurality of individual heat exchange cells. Each cell is sealed so as to contain a plurality of longitudinally extending liquid coolant channels which run inside the cell. Adjacent cells are sealed together at their outer perimeters to form a plurality of gas flow channels which extend longitudinally along a main length direction of the heat exchanger. A first end of the heat exchanger is substantially rectangular, where the second end of the heat exchanger has a pointed or angled shape.
In use, the liquid may flow through the cells in a direction opposite to the direction in which the gas flows through the cells, so that contra flow between the liquid coolant and the gas to be cooled occurs, with the liquid and gas being isolated from each other. Heat transfers from the gas to the liquid through the thin plate walls.
However, in the general case, liquid may be passed in either direction along the length of the cells by reversing the coolant flow direction, although the heat exchanger may be marginally more efficient with the coolant flowing in the opposite direction to the gas flow direction (contraflow) than with the gas flow and coolant flow running along the length of the heat exchanger in the same direction.
In use, the second heat exchanger is placed in an exhaust gas circuit of an internal combustion engine so that the gas flow comprises recirculated exhaust gas, and the liquid coolant flow cools the exhaust gas.
In the second embodiment heat exchanger, the gas inlet manifold 902 is designed to accept gas from a direction along a main length axis of the heat exchanger, and gas is outlet from the heat exchanger via the outlet tube 903 in a direction perpendicular to a main length axis of the heat exchanger. The gas inlet manifold 902 transfers gas directly into a plurality of gas passages which extend between adjacent cells along a main length of the heat exchanger to the outlet end, at which the gas flows into an outlet passage 923 within the heat exchanger, the outlet passage extending in a direction transverse to the main planes of the heat exchange plates. Hence, the gas is inlet in a direction along a main length direction of the heat exchanger, and is outlet in a direction perpendicular to a main length of the body of the heat exchanger (although as stated above, the device will also operate with good efficiency with the gas flowing in the opposite direction). Preferably, a width of the each gas passage along its main gas flow region between adjacent cells is a distance of no less than 3mm.
The liquid coolant is connected to the heat exchanger by a substantially "L" shaped liquid inlet tube 904 so that a connecting fluid pipe (not shown) can run in a plane parallel to a set of planes which intersect the heat exchange plates, with the liquid entering the heat exchanger in a direction transverse or perpendicular to the planes which intersect the heat exchange plates. A liquid inlet passage is formed within the body of the heat exchanger by the plurality of heat exchange plates, each of which has its own liquid inlet aperture, the plurality of liquid inlet apertures forming the inlet passage within the main body of the heat exchanger.
Similarly, the liquid coolant exits from the heat exchanger through a liquid outlet passage extending in a direction transverse or perpendicular to the planes which intersect the heat exchange plates, passing into the liquid outlet tube 905, which is also substantially "L" shaped, and which connects to a fluid pipe (not shown) which may extend in a plane parallel to the planes which intersect the heat exchange plates. Each individual heat exchange plate has a liquid outlet aperture, whereby the plurality of liquid outlet apertures together form the internal liquid outlet passage within the main body of the heat exchanger. The liquid outlet tube 905 is connected to the internal outlet passage. Hence, the heat exchanger can form a compact unit with the liquid being supplied by a pair of connecting pipes which lay compactly adjacent the heat exchanger.
For additional mechanical strength, the stack of heat exchange plates may be secured together by a plurality of externally located connecting members 906 - 909, which also provide a means of connecting the second heat exchanger to a support. The two outermost heat exchange plates each have a set of peripheral protruding anchor points 910 - 913 respectively on a second outer plate 927; and 914 - 917 respectively on a first outer most plate 926, each connecting member 906 - 909 being attached to a pair of opposite said anchor points, one of which is on the first outer most plate, and the other one of which is on the second outer most plate, so that the connecting members connect the outermost plates together, bridging across the stack of plates in a direction transverse to the planes which intersect the individual heat exchange plates.
The connecting members 906 - 909 each comprise a cylindrical tube, the ends of which are brazed to the anchor plates 910 - 913. In use, the connecting members provide a fitting points for fitting the second heat exchanger to an engine block or other vehicle mounting point, by passing bolts through the hollow tubes to attach them to the engine block or other mounting surface.
On the second side of the heat exchanger opposite to the liquid coolant inlet 904, there is provided a first bleed valve 924, which allows any gas in the liquid circuit to be bled from the liquid coolant path. At a position on the second side of the heat exchanger opposite to the liquid coolant outlet tube 905 there is provided a second bleed valve 925, which connects with the liquid outlet passage in the core, and which can also be used to remove air or gas from the liquid coolant path of the heat exchanger. Each bleed valve is attached to the heat exchanger along a direction of an internal inlet or outlet liquid passage.
Each internal inlet or outlet coolant passage has a teardrop shaped or cam shaped cross-section, arranged such that a protruding part of the aperture is located at a highest point of the passage, so as to allow gas to flow to the top of the passage, and to stop gas becoming trapped in the core. As mentioned elsewhere in this description, the coolant flow can be reversed, so the inlets and apertures may become swapped over in function.
Referring to figure 15 herein, there is shown schematically a core of the second heat exchanger in view from the first side, being the side to which the coolant inlet tube 904 and coolant outlet tube 905 are attached. And outermost cover plate is not shown, except for the anchorage points 914 - 917.

Cell Types

The second heat exchanger comprises three types of cells as follows:

an inner cell, comprising a first plate and the second plate;
an outer left hand cell, on a first side of the heat exchanger comprising a third plate and a second plate; and
an outer right hand cell, on a second side of the heat exchanger, comprising a fourth plate and a second plate.

Each cell type comprises two separate plates. Overall, there are six different plate types which can be divided into plates having a first formed shape including coolant channel indentations which all use the same forming tool, and differ only by virtue of the regions where apertures are pierced through the basic formed shape; and plates of a second formed shape, which are formed by a second forming tool, having a plurality of coolant channel indentations and which differ only by virtue of which regions have apertures pierced or material removed from the basic second formed shape; and plates of a third formed shape, being the outer plates which do not have any coolant channel indentations.
Referring to figure 16 herein there is shown in view from one side a first type of cell 1600, comprising a first plate 1601 and a second plate 1602 joined together by a leak tight weld 1603 extending around a coolant periphery of the second plate, and joining the second plate to the first plate.
The first plate 1601 comprises an elongate substantially flat plate which intersects with a plane, the first plate having a central region containing a plurality of elongate indentations which extend along a main longitudinal axis of the plate. The plurality of indentations are separated from each other by a plurality of flat fin portions extending along a main longitudinal axis of the plate, alternating between adjacent elongate indentations.
An outer perimeter of the first plate is formed into a flange or skirt 1604 which extends around the outside of the first plate in a direction transverse to a main plane of the first plate. At the first end of the plate, being the gas inlet end, the skirt is absent, to allow gas flow into the cell.
At a first end 1605 of the first plate, there extends a flat portion of the plate 1606, which in use forms part of the side of the heat exchanger. At a second end 1607 of the first plate there is a further flat portion 1508 which forms part of the side of the heat exchanger and seals off one end of the gas outlet passage of the central core of the heat exchanger. The second end of the first plate comprises a substantially triangular shaped portion having a rounded corner.
At the first end of the cell the first and second plates form a first aperture 1610 to allow coolant to flow between the first and second plates and into the plurality of longitudinal passages extending inside the cell, and at the second end of the cell, the first and second plates form a second aperture 1609 for exiting liquid coolant from the inside of the cell. In use, the first aperture 1610 forms a liquid coolant inlet to the cell, and a second aperture 1609 forms a liquid coolant outlet (although, the heat exchanger can be connected with direction of flow of the liquid coolant reversed, making the second aperture 1609 an inlet aperture, and the first aperture 1610 an outlet aperture). The second aperture 1610 is teardrop or cam shaped, comprising a circular aperture with a peripheral extending part in the plane of the circle, so that in use, the extending parts is at a highest point, and any gas forming in the liquid coolant rises into the void formed by the extending part, from where it can be bled from the heat exchanger. Similarly, the first aperture 1609 has a similar teardrop or cam shape, but with the pointed part of the teardrop extending downwardly, so that if the heat exchangers fitted the other way up, the pointy part of the aperture will be uppermost, and any gas in the coolant liquid will collect in the pointed part of the second+ aperture.
The second plate 1602 is formed from a second sheet of material, and is welded to the first plate 1601. The second plate comprises a plurality of elongate indentations 1612 which extend longitudinally along a main length of the second plate, and which are positioned opposite the plurality of indentations in the first plate, to form a plurality of longitudinal internal channels through which a liquid flows. The second indentations protrude out of a main plane which is coincident with the main metal sheet of the second plate.
With the plurality of longitudinal liquid carrying channels are formed by the plurality of indentations on the first plate, which lie opposite and extend in an opposite direction transverse to a main central plane of the cell to the first indentations of the first plate. Hence, a main central plane of the cell extends at the interface where the first and second plates touch each other, there being a parallel first outer plane which intersects with the outer extremity of the first set of longitudinal channels, and a second outer plane which intersects the main outer extremities of the second set of longitudinal channels of the second plate. A first plurality of flat fin portions extend between the first set of indentations on the first plate, and a second's plurality of flat fin portions extend between the second set of indentations on the second plate. The first and second flat fin portions lie opposite each other and touch each other as the two plates are mated together, and the two plates are welded together along each fin portion between the channels, and around the coolant periphery of the second plate, so that the liquid coolant channel is contained within the second plate, and a plurality of individual longitudinal channels within the cell are isolated from each other by the intervening fin portions. The welds along the fins do not need to be leak tight, since their primary purpose is to give mechanical strength to the cell, and the coolant is contained within the leak tight weld which extends around an outer perimeter of the second plate, joining to the first plate.
At a first end of the second plate, there is provided a substantially flat portion 1613 which forms a distribution chamber or manifold for channeling liquid between first aperture 1509 and the first ends of the plurality of internal fluid channels 1612. Similarly, at a second end of the second plate there is provided a second substantially flat portion 1614 which forms a distribution manifold or chamber for transferring fluid from the second ends of the plurality of internal channels and a second aperture 1610. The shape of the distribution chambers 1613,1614 is designed so as to create a flow of coolant all the way across the gas flow, to minimise dwell of liquid in the distribution chambers, and thereby minimise the risk of the liquid boiling, and to ensure a relatively even distribution of liquid coolant across all of the plurality of liquid channels. In the embodiment shown, each distribution chamber in plan view has a substantially triangular shape, with a bulbous round portion at a lower corner of the triangle, in which an aperture is positioned. Internally, the distribution chamber is a substantially constant width, with one or a plurality of projecting indentations which extend into the distribution chamber there within. In plan view, the area is substantially tapered or wedge shaped, with a circular region at one end, approximately in the form of an acute angled triangle. This shape helps prevent "dead zones" where the liquid flows more slowly and therefore is more vulnerable to boiling.
As shown in figure 16 on the surface of the second plate, both the first and second plates each comprise a plurality of studs or indents 1611 distributed over the plates in the region of the plurality of longitudinal channels. These indents are distributed evenly in rows and columns, and when the first cell is placed adjacent to another cell, the indents project into a gas channel formed between the cells.
Each elongate indentation is periodically modified along its length by a plurality of discrete indentations which form projecting stud portions 1611 which project outwardly beyond a plane joining the outermost surfaces of the longitudinal indentations on the outside of the plate. These projecting studs have a primary function of projecting into a passage or channel between adjacent cells through which there is a gas flow, in order to introduce turbulence into the gas flow. The depths of the indentations may be varied as a design parameter, to vary the amount of protrusion into the gas channel flowing on the outside of the cell between adjacent cells. Different patterns of studs may be provided, but in a best mode embodiment, as shown on the surface of the second plate 1602 in figure 16, and arrangements of studs in rows and columns, in which the studs lie on corners of a parallelogram gives an optimised turbulent gas mixing.
In the region of the first distribution region 1613, there are a pair of indents, which extend into the coolant flow, and similarly, in the region of the second distribution area 1614 there are provided a pair of indents extending into the coolant flow.
The projecting or protruding studs 1611 may also have a secondary purpose of acting as spacers between adjacent cells. However their function as spacers is not essential for the operation of the heat exchanger, because the spacing between adjacent cells is determined by the peripheral flange 1603 which extends around the outside of the first plate 1601.
Referring to figure 17 herein, there is illustrated schematically a second type of cell, which is used sandwiched between two of the first type of cells of figure 16 to make a stack of cells comprising the main body of the heat exchanger. The second cell comprises a third plate 1700 and a second plate 1602.
Third plate 1700 is substantially similar to the first plate, but with the following exceptions. A first end 1701 of the third plate has a hollow cutout between the laterally extending flange portions 1702, 1703 extending either side of the first end, which, in a stack of plates in the assembled heat exchanger forms an inlet chamber for the gas, prior to entering between the region of the cells which contain the laterally extending liquid coolant channels. Further, at the second end of the third plate, there is a cutout aperture region 1704, which in the first plate is a solid sheet of metal, but in a third plate forms an outlet passage for gas leaving the heat exchanger. At the second end, the gas outlet aperture 1705 is bounded by a second end of the second plate, and a peripheral skirt or flange portion 1706 which extends along an upper and lower periphery of the second end of the third plate.
Similarly to the first cell, the third cell comprises a plurality of longitudinally extending fluid channels 1707 formed by opposing elongate indentations in the third plate and the second plate, alternating with a plurality of flat fin portions of the second and third plates which are welded, and thereby separating the plurality of adjacent elongate liquid channels inside the cell. The plurality of liquid channels extend between a first end and a second end of the second plate, and between a first aperture 1708 and a second aperture 1709. In the second cell, the third plate has a first aperture 1710 and a second aperture 1711, which lineup with the first aperture 1708 of the second plate and the second aperture 1709 of the second plate respectively, so that in the assembled heat exchanger, the first aperture is form a first liquid coolant passage of the second aperture is form a second liquid coolant passage through the core of the heat exchanger.
At the first end of the second plate, there is a first liquid distribution manifold 1712, formed between the material of the second plate and the third plate for channeling liquid between the first aperture is and the first ends of the internal liquid channels; at a second end of the second plate, there is formed a second liquid distribution manifold 1713, which channels liquid between the second ends of the liquid carrying channels and the second apertures. Each liquid distribution manifold comprises a substantially flat volume, substantially triangular in plan view and having a rounded corner which accommodates the apertures.
All other features of the second cell are identical to the corresponding features of the first cell.
Referring to figure 18 herein, there is shown schematically in perspective view from one side, a first outer plate 1800 of the heat exchanger for fitting to the first side, and which forms an outer facing surface of the assembled heat exchanger. The first outer plate comprises a substantially elongate plate of sheet metal material, stamped out and pressed into a shape which comprises an elongate rectangle, having at a first end a waist portion 1801 having a depth approximately 80% of a full depth of the plate; at a second end, a rounded triangular nose section 1802; a first aperture 1803 for attachment of a second liquid carrying tube 905; a second aperture at the second end, for attachment of a first liquid carrying tube 904; and first to fourth anchorage points 914 -917 as previously described.
Referring to figure 19 herein, there is illustrated schematically in perspective view, a second outer plate 1900 of the heat exchanger, which is fitted to a second side of the heat exchanger, protecting the core cell assembly, and providing an outer facing surface of the assembled heat exchanger. The second outer plate comprises a substantially elongate plate of sheet metal material, stamped out pressed into a shape consisting of an elongate rectangle having a first end 1901 and a second end 1902; said first and comprising a narrow waist portion 1903 having a depth of around 80% of the depth of the main central portion of the second outer plate; at a first end, a first drain aperture 1904 which aligns with the first liquid channel inside the core of the heat exchanger, and which is used to bleed off any gas formed in the first liquid channel; at the second end, a second drain aperture 1905 which is used to bleed gas from the first liquid channel if installed the other way up, and a gas outlet aperture 1906 to which is connected to the gas outlet 923; and a second plurality of anchor points 910 - 913, each of the second anchor points being formed in a bent "dog leg" so that they lie in a plane parallel to and adjacent the main plane passing through the main body of the second outer plate.
The sheet material of the first and second outer plates is preferably of thicker but lower grade material than the sheet material of the metal used to make the heat exchange plates inside the core of the heat exchanger.
Referring to figure 20 herein, but the shown schematically a cutaway view along the line B - B' shown in figure 11 herein. This section shows a second end of the heat exchanger in which a plurality of cells 2000 - 2007 are assembled into a stack to form the main body of the heat exchanger. At the second end, the internal longitudinal passages which carry liquid coolant flow into a liquid coolant inlet manifold section 1600 within the cell comprising a substantially flat portion of the first, second and third plates which make up the cells. This manifold inlet section channels liquid from the coolant inlet passage 1601 into the plurality of longitudinally extending coolant passages extending through the main body of each cell.
As shown in cutaway view, and taking a first cell 2000 as an example, the first cell comprises a plurality of first to thirteenth liquid carrying channels 2008 - 2020 inside the cell, arranged side by side, and separated by a plurality of fin portions 2021 - 2033. The first, fourth, seventh, tenth and thirteenth channels shown in cutaway view in figure 20 are cut at a location where the channel is expanded to accommodate the indents or studs. In the embodiment shown in figure 20, the studs contact each other, but in the general case, the spacing between adjacent cells is determined by the outer flange portions of each cell 2034 - 2041.
The two plates of each cell are welded along each fin, and around a coolant perimeter of the second plate, so that the internal liquid carrying channels of the cell are leak tight. Laser welding along the fins, and around the periphery of the cell gives mechanical strength to the cell and allows the cell to operate under a high liquid pressure.
Between adjacent cells, there are provided a plurality of gas conducting channels 2042 - 2048, through which gas flows through the heat exchanger core.
Figure 21 herein shows a section across the line B - B' in figure 11 herein, showing an internal structure of the heat exchanger through the liquid distribution manifolds of the cells at the second end of the heat exchanger. Preferably a width w1 of the gas passage between adjacent cells is no less than 3mm in the main region of the gas passage, and at the regions where the coolant inlet manifolds are present, the width w2 of the gas passage is no less than 2mm. This helps with the regeneration of the gas passages, by removal of any soot or carbon deposit which might be deposited within the gas passage.
Figure 22 herein shows a section across the line C-C' in figure 11 herein showing an internal structure of the second heat exchanger.
Figure 23 herein shows a section across the line D-D' in figure 11 herein, showing an internal structure of the second heat exchanger along the length of the heat exchange cells.
Figure 24 herein shows a section across the line E-E' in figure 11, showing an internal structure of the second heat exchanger.

Heat Transfer and Fluid Flow

An advantage of arranging the fluid flow was so that the liquid flows through the centre of the heat exchange cells with the gas flowing between adjacent heat exchange cells is that a full surface area of the cells which is in contact with the gas act as heat exchange surfaces. This means that the material comprising the fins, as well as the part of the material comprising the longitudinal coolant channels act as heat exchange surfaces having substantially similar heat transfer characteristics. In the case of the material comprising the indent forming the longitudinal liquid channels, heat is transferred directly from the gas on one side of the metal, through the metal, to the liquid coolant on the inside of the coolant channel. For gas which contacts the fins, heat is conducted from the gas to the metal of the fins, and then transfers by conduction laterally to the metal walls of the coolant channels, and to the coolant flowing in those channels. The metal walls comprising the fin portions of therefore not significantly hotter than the metal walls comprising the coolant channels.
Figure 25 herein shows a velocity contour gas flowing in a middle plane, at gas channel 7, within the second heat exchanger as gas flows from the gas inlet to the gas outlet between adjacent cells. As shown in figure 25, each protrusion which extends into the gas flow causes in its wake a substantially teardrop shape eddy, which promotes turbulent mixing of the gas behind the protrusion, in the direction of main gas flow.
Figure 26 shows a velocity vector plot of gas flowing in gas channel 1, in a middle plane view, from the gas inlet end towards the centre of the second heat exchanger. In figure 26, gas is shown flowing from the first end of the cell to the second end. At the first end of the gas channel on the left-hand side in figure 26, gas enters the channel with substantially laminar flow. The gas expands laterally across a depth of the cell, around the coolant outlet channels shown as a circle, and over the liquid distribution manifold, into the main heat exchange area of the cell, where the plurality of studs project into the gas channel. The plurality of studs disrupt the gas flow, to cause turbulence, which promotes greater heat exchange between the gas and the metal surface of the plates compared to laminar flow. Each stud creates eddies in the gas flow which disrupt the gas flow both in the lateral direction across a depth of the adjacent cells, and in a direction across a width of the gas channel between cells. The coolant outlet channel also causes turbulence in its wake. Once the gas flow is past the coolant outlet and into the main body of the core, the gas flow is very homogeneous, having even turbulence across the whole depth of the cells.
Whilst the stud arrangement causes significant increase in turbulence in the gas flow, and thereby increases the rate of heat transfer between the gas and the liquid coolant, the existence of the studs in the liquid channels does not cause significant increase in turbulence to the liquid coolant flow. Hence this means that the gas flow has been affected, without significantly affecting the liquid coolant flow. This is not achievable in prior art coolers having channels which have a serpentine liquid coolant path, where introduction of turbulence creating indents into the gas channel also introduce coolant path also introduce turbulence into the coolant channel.
Figure 27 shows a velocity vector plot of gas flowing in gas channel 1, in a middle plane view, from the centre of the second heat exchanger towards the second end. In figure 27, the gas flow is reversed from that shown in figure 26 (heat exchanger connected the gas flow in the opposite direction), for the purposes of illustration. The gas flows through the second gas passage at the second end of the cell and through the gas passage between cells. The plurality of studs create turbulence and the gas flow, which applies irrespective of which direction the gas flow is connected through the heat exchanger.
Figure 28 shows a velocity vector plot at a second end of heat exchanger, viewed in a direction perpendicular to the main planes of the heat exchange cells, showing gas flow towards the second end of the heat exchanger, and exhaust of gas through the gas outlet passage. At a position where adjacent cells have their coolant distribution chambers, the gas flow is locally restricted, over part of the depth of each cell as shown in figure 28. In figure 28, the gas is shown flowing from the first end to the second end of the heat exchanger.
Figure 29 herein shows flow lines of gas flowing through the second heat exchanger from the gas inlet to the gas outlet in three-dimensional view; and
Figure 30 shows a velocity vector plot of coolant flowing through a cell at the middle plane of the cell from a coolant inlet at the second end of the second heat exchanger, towards a coolant outlet at a first end of the second heat exchanger, and showing mass flow fraction as a % for individual coolant channels 1 -13 across a depth of the heat exchange cell. In figure 30, the flow of liquid passes from left to right, but since the second plate is symmetrical, a flow in the opposite direction would give a corresponding opposite distribution of liquid flow.
As seen in figure 30, all liquid channels have a mass flow fraction in the range of 6.24% to 9.28% of the total liquid mass flow, the average mass flow being 7.69% for a cell having 13 liquid channels. Hence, a maximum deviation from the average mass flow of liquid through the channels, of the total mass flow of 7.69% is 1.59%, or 20.7% of the average mass flow.

Gas Path

The layout of the gas path has the following features:

1. The height of the gas path is set by the outer joint and the cell pad heights. The height of the gas path does not affect the coolant path other than the cell studs cause a widening of the coolant path in a very local area.
2. The gas path uses a series of 'pins' or studs formed into the plate of the coolant cell to disrupt and mix the gas flow. The positioning of these pins relative to each other and the gas inlet and outlet is closely control to maximise heat exchange and minimise gas pressure drop.
3. The geometry of the gas channels is designed to maximise the heat transfer for a given plate unit area ie W/m².K.kg For a given customer specification the K differential temperature of the two fluids and the kg mass flow of the gas is set and the W is the requirement the m² of the plate needs to be minimised to reduce weight, size and cost.
4. The low coolant channels and the pin alignments cause the gas to flow in substantially a direct path from the gas inlet header to the gas outlet header.
5. The height of the gas path and the pins are designed to maximise the regeneration of the engine deposits on the gas side of the cooler. This is crucial in maintaining performance as close as possible to the original clean condition.
1. a. The height of the gas path in the main flow path is at least 2mm this ensures that there is not a small annulus that can become fully clogged from the engine deposits.
2. b. The design and spacing of the pins whilst giving good gas flow disruption and gas mixing does not have too large eddies. This allows the gas flow to effectively scavenge the engine deposits from the plates.
6. The gas pressure contained within the void formed by one cell to the next exerts a force trying to push the cells apart. This will result in the two outermost cells having a force caused by the gas pressure trying to move the cells apart. The cells react some of this pressure around their outer edges where each cell is joined to the next cell. The two outer most cells react not only around the outer edge but also in theirs centres on the two clamping plates. This arrangement allows a small amount of relative movement between cells to take place without exceeding a safe level of stress. This movement helps with the regeneration of the engine deposits on the gas side of the plates.

Gas Inlet Interface

The gas inlet interface has the following features:

1. The gas inlet interface at the start of the coolant channels is over at least 80% of the width of the plate.
2. By having at least 80% of the width of the plate the gas distribution is sufficiently even to ensure high levels of heat exchange and low gas pressure drop.
3. To save on plate material scrap when forming and cutting out the plates from strip the coolant interfaces can be placed inside the 'normal' width of the plate.
4. The ends of the cells form a chamber to allow the gas to flow into and from the cooled section of the cell without restricting or channelling the gas flow. This is important for both good gas distribution across the width of the cell and reduced gas pressure drop.

By using the cells to form the gas headers there is a cost saving over the traditional prior art bulkhead and over prior art formed, fabricated or cast headers welded to the stack.
Also by replacing the prior art relatively thick walled bulkhead and gas header with the relatively thin walled cell edge, the stresses due to differential thermal expansion across components at or near gas temperature and components at or near coolant temperature are much reduced.

Fabrication - External Joints

Fabrication of the second heat exchanger follows an equivalent method to the first heat exchanger described hereinabove. Individual plates are formed by pressing. As mentioned above, there are two basic plate shapes, being the first plate and the second plate for construction of the cells, and to further basic plate types being the first outer plate and the second outer plate which are of thicker material.
Taking as an example and internal cell having a first plate and the second plate as is hereinbefore described, the second plate is positioned opposite the first plate, touching the first plate and laser welding around a periphery of the second plate, to weld the perimeter of the second plate to the first plate, producing a leak tight weld. The portions of flat metal forming the fins between adjacent coolant channels are also laser welded, but these laser welds do not need to be leak tight, since coolant cannot escape from the coolant channels between the first and second plates due to the peripheral weld around the second plate. The formation of the first and second outer cells is similarly made, the only difference between the outer cells and the inner cells in the core of the heat exchanger being the cut out areas at the locations of the coolant inlet's and outlets, and the gas channel at the second end of the cell.
Each cell is pressure tested and visually inspected to make sure that it is robustly welded without any leaks.
The cells are spaced apart by the peripheral skirts which extend around the outside of the cells. When pressed together, the regions of metal around the coolant apertures between adjacent cells touch each other, and the skirts touch each other. In some embodiments the studs which project into the gas passages may have been designed so as to touch each other in the finished heat exchanger also. The first and second outer plates are fitted by pressing them to the core of the heat exchanger. Further, the connecting members between the anchor points on the first and second plates are inserted. The flange at the inlet end of the heat exchanger is located around the open ends of the cells. The outer flange helps to locate the first ends of the cells together. The assembled heat exchanger can be held together in a clamp, or under a press or mass for the next operation of brazing or soldering.
The whole assembly is brazed or soldered by soldering around the outer flanges connecting them together, and soldering inside the coolant passages, soldering the coolant apertures of adjacent cells to each other, brazing or soldering the peripheral flanges or skirts to each other, and brazing or soldering the end flange at the first end of the heat exchanger. At the same time, the outer plates are brazed or soldered to the core, by brazing or soldering the flanges and, where present, around a perimeter of any coolant apertures and gas apertures.
The coolant inlet and outlet tubes are fitted and brazed or soldered to the coolant inlet and outlet passages.
After assembly, the whole heat exchanger is visually inspected for defects in brazing or soldering, and if any are found, those defects areas can be rectified by further brazing or soldering. The whole assembled heat exchanger may be gas pressure tested.
There are two types of cell to cell joint:

a. A round joint joining one coolant interface to the next coolant interface.
b. An edge or skirt joint sealing one cell to the next cell and enclosing the gas path.

The round cell to cell joint is visible and accessible from the coolant inlet/outlet hole on the outer most cell. Thus it can be reworked as a final assembly.
The edge joint of the skirt is an external joint and is both easily visible and re-workable.
By this design all joints that are not checked and inspected as subassemblies can be reworked as a final assembly.

The Case and Bulkhead.

Prior art coolers have a case that encloses the coolant that flows around tubes or plates that carry the gas.
Coolant pressure on the case applies a force on the case trying to expand the case. This force is to some extent transferred to the prior art traditional coolers bulkhead. The coolant is also applying a force to the bulkhead of a traditional prior art cooler pushing the bulkheads out of the cooler.
A prior art cooler with a case and either tubes or plates has a temperature differential between the case and the tubes or plates. The case temperature will be slightly lower than coolant temperature due to heat loss to the ambient. The tubes or plates will be above coolant temperature due to the heat transferred from the gas. A traditional prior art cooler will have forces on the bulkhead caused by the differential expansion of the tubes or plates and the case.
The stresses due to coolant pressure and differential expansion combine with the thermal stresses at the gas inlet bulkhead to cause potentially damaging levels of stress. This is an area of failure typically seen on a prior art traditional cooler.
The novel design disclosed herein, having no case or bulkhead, and as discussed earlier lowers thermal stress at the gas inlet, removes this typical cause of failure.
The above embodiment heat exchangers may provide an improved heat exchanger compared to prior art types, and which have a relatively lower gas pressure drop compared to conventional gas to liquid heat exchangers, which have reduced volume for a specified amount of cooling capacity, and which have lower weight, for a specified amount of cooling capacity due to the reduced amount of liquid coolant within the heat exchanger.
The above embodiment heat exchangers effectively provide a decoupling of gas flow design from liquid flow, so that the liquid flow direction can be reversed through the heat exchanger without significantly affecting the rate of heat transfer from the gas to liquid. This means that both the liquid and the gas can be fed through the heat exchanger in the same direction, or in opposite directions in any combination without significantly affecting the heat transfer performance of the heat exchanger. The features which give rise to this versatility include the studs which project into the gas channel, containment of the liquid coolant within the cells, and the symmetry of the second plates which allow passage of coolant from either end with no significant difference in coolant flow characteristics. The presence of the stud features, which are formed as part of the indentations which form the liquid coolant channels, does not significantly affect the flow of coolant in the liquid coolant channels. The studs produce a disproportionate amount of turbulence in the gas flow, compared to the amount of turbulence that they produce and the liquid flow. Turbulence the liquid flow is of no particular advantage since it does not materially affect heat transfer rate, whereas turbulent and the gas flow significantly increase its heat transfer rate. Therefore, the studs improve heat transfer rate from the gas to liquid, without introducing significant turbulence and pressure drop into the liquid flow, and additional wasted coolant volume
Further, the heat exchangers are of a modular design, which can include a lesser or greater number of cells in the core to provide a reduced or increased heat transfer capacity as required, without significant changes to manufacturing process.

Claims

A gas to liquid coolant heat exchanger for transferring heat between a gas and a liquid coolant, said heat exchanger comprising:
a plurality of heat exchange cells;

each said cell comprising a liquid coolant inlet and a liquid coolant outlet;

each said cell comprising a pair of plates each said plate having a plurality of grooves which form a plurality of liquid coolant channels between said plates, extending between said liquid coolant inlet and liquid coolant outlet;

characterised in that

each said cell contains said liquid coolant within said cell between said pair of plates.
The heat exchanger as claimed in claim 1, wherein said plurality of liquid coolant channels extend substantially parallel to a main length of said cell.
The heat exchanger as claimed in any one of the preceding claims, wherein an inner perimeter of one of said plates is joined to the other one of said plates, to form a liquid tight seal for containing liquid within said cell, and wherein said liquid coolant can enter or exit said heat exchange cell only through said liquid inlet and outlet.
A heat exchanger as claimed in any one of the preceding claims, wherein:
a said heat exchange cell comprises a distribution manifold for distributing said coolant between a said coolant inlet, and a said plurality of liquid coolant channels within said cell,

characterised in that said distribution manifold is arranged to control and direct the flow of said liquid coolant such that there is adequate flow of said coolant across a gas inlet interface to reduce and/or eliminate the occurrence of said coolant boiling.
A heat exchanger as claimed in any one of the preceding claims, wherein said cells are designed to control and direct the flow of coolant such that there is adequate flow of coolant in all the longitudinal coolant channels to reduce and eliminate the occurrence of coolant boiling.
A heat exchanger as claimed in any one of the preceding claims, wherein said cells are designed to minimise a volume of coolant within the heat exchanger, relative to a gas flow capacity of said heat exchanger.
A heat exchanger as claimed in any one of the preceding claims, which 'decouples' the geometry of the coolant side and the gas side of a heat exchanger such that the coolant performance and the gas performance can be maximised substantially independently of each other.
A heat exchanger as claimed in any one of the preceding claims which has a heat exchange capacity of >0.25 W/m².K.kg, at 98% effective or greater, whilst having low pressure drop.
A heat exchanger as claimed in any one of the preceding claims wherein in a main part of the heat exchanger, both said gas and said liquid each flow in paths which follow a substantially longitudinal direction along a main length of said heat exchanger.
A heat exchanger as claimed in any one of the preceding claims which has no outer casing, no bulkhead, and no separate gas header.
A heat exchanger as claimed in any one of the preceding claims, comprising a gas inlet and a gas outlet, wherein each one of said gas inlet and said gas outlet is capable of interfacing in either a longitudinal direction relative to a main length direction of said heat exchanger, or perpendicularly relative to said main length direction.
A heat exchanger as claimed in any one of the preceding claims, comprising a coolant passage which can be used as a coolant inlet or outlet passage,
characterised in that the coolant is able to vent any gas formed within said coolant within said coolant passage.
A heat exchange cell for a gas to liquid heat exchanger as claimed in any one of the preceding claims, said cell comprising:
a first plate and a second plate;

at least one of said plates having a plurality of grooves which form a plurality of liquid coolant channels between said plates,

characterised in that

each said cell contains said liquid coolant within said cell between said plates.
The heat exchange cell as claimed in claim 13, wherein an outer perimeter of said second plate fits within an outer perimeter of said first plate, and said outer perimeter of said second plate is sealed to said first plate by a continuous weld extending around said outer perimeter of said second plate.
The heat exchange cell as claimed in claim 13 or 14, comprising a plurality of fin regions located between said plurality of grooves, wherein said pair of plates are welded to each other along said fin regions.
The heat exchange cell as claimed in any one of claims 13 to 15, comprising a liquid inlet and a liquid outlet, for allowing liquid into and out of a cavity between said first and second plates, said liquid inlet and outlet being located within an area bounded by an outer perimeter of said second plate.
The heat exchanger as claimed into any one of claims 13 to 16, comprising a liquid distribution chamber for distributing liquid from or to a liquid inlet or outlet and said plurality of liquid coolant channels inside said cell, wherein said liquid distribution chamber distributes liquid between said plurality of coolant channels such that difference in mass flow of liquid between a liquid coolant channel having a lowest mass flow and a liquid channel having a highest mass flow is no more than 23% of the mass flow of the average channel mass flow.
A gas to liquid heat exchanger as claimed in any one of the preceding claims comprising:
a plurality of heat exchange cells, each said cell comprising a first plate and a second plate;

wherein each said heat exchange cell comprises a liquid inlet aperture and a liquid outlet aperture;

each said plate comprising a sealed outer perimeter, and a plurality of internal fluid channels;

each heat exchange cell having its coolant perimeter sealed independently of the coolant perimeter of each other said heat exchange cell;

said plurality of heat exchange cells arranged side-by-side in a stack arrangement;

wherein said plurality of heat exchange cells are sealed to each other by an outer perimeter seal around their respective outer perimeters, to form a plurality of gas channels extending between said plurality of cells.
The heat exchanger as claimed in claim 18, wherein said plurality of heat exchange cells are sealed to each other by a liquid inlet seal, which joins the respective inlets of the heat exchange plates together to form a liquid inlet passage.
The heat exchanger as claimed in claim 18 or 19, wherein said plurality of heat exchange cells are sealed to each other by a liquid outlet seal, which joins the respective outlets of said heat exchange plates together. To form a liquid outlet passage.
The heat exchanger as claimed in claim 18, wherein each said cell comprises an inlet aperture and an outlet aperture; and
said plurality of heat exchange cells are sealed to each other by an inlet seal, which joins the respective inlets of the plurality of heat exchange plates together to form a common inlet passage; and
said plurality of heat exchange cells are sealed each other by an outlet seal, which joins the respective outlets of said heat exchange plates together to form a common outlet passage; and
said plurality of cells are joined together and said inlet seals, said outlet seals and said outer perimeter seal formed in a single sealing operation.
The heat exchanger as claimed in any one of claims 18 to 21, wherein a fluid connector for connecting said heat exchanger to a fluid circuit comprises a tubular collar brazed or soldered to a region around a perimeter of an aperture in a said plate, said region presented on an outer plate of said heat exchanger.
A method of manufacture of a gas to liquid coolant heat exchanger as claimed in claim 1, said method comprising:
individually forming each of said plurality of heat exchange cells, each comprising a respective first plate and a second plate, by joining said first and second plates together with a continuous joint extending around a perimeter of said second plate to form a cavity between said second plate and said first plate, through which a liquid coolant may flow;

individually testing each said cell to check for fluid leaks in said cavity;

joining said plurality of individual heat exchange cells together by placing said plurality of cells into an assembly of cells;

forming an outer joint around said plurality of cell perimeters;

forming an inlet joint joining together a plurality of inlets of said cells, and

forming an outlet joint by joining together a plurality of outlets of said plurality of cells.
The method as claimed in claim 23, further comprising leak testing said assembly of cells.
The method as claimed in claim 23 or 24, wherein said process of individually forming said cell comprises performing a plurality of second joints between said first and second cells, said second joints located between a plurality of grooves in said first and second plates, which form a plurality of liquid channels in said cavity, and within an area bounded by said continuous joint.
The method as claimed in any one of claims 23 to 25, wherein each said heat exchange cell is formed by:
forming a said first plate and a said second plate;

arranging said first and second plates so as to lie opposite each other;

joining said second plate to said first plate by forming a continuous joint around a perimeter of said second plate; and

joining said first and second plates at a plurality of locations over a region extending within said perimeter of said second plate.
The method as claimed in any one of claims 23 to 26, wherein said plurality of cells are joined together by brazing or soldering.
The method as claimed in any one of claims 23 to 27, wherein said first and second plates are joined together by laser welding or by resistance welding.
The method as claimed in any one of claims 22 to 27, further comprising pressure testing each said cell to check for leaks in said perimeter joints, prior to assembling said plurality of heat exchange cells together.
The method as claimed in any one of claims 23 to 29 further comprising pressure testing the complete heat exchanger assembly after the formation of said outer perimeter joint around said plurality of cells and after the formation of said inlet joint and said outlet joint.
The method as claimed in any one of claims 23 to 30, further comprising:
locating a tubular collar at a region around a perimeter of an aperture in a said plate, said region presented on an outer face of said heat exchanger;

brazing or soldering said collar to said plate to form an attachment point for attaching a coolant inlet or outlet tube.
A heat exchange cell for a gas to liquid heat exchanger as claimed in claim 1, said cell comprising:
a first plate and a second plate;

at least one of said first and second plates comprising a plurality of elongate grooves, said plurality of grooves forming a plurality of liquid coolant channels inside said cell;

at least one of said first and/or second plates having a plurality of outwardly projecting studs, which project in a direction outwardly from a plane which intersects an outer surface of a said plate at the position of said plurality of grooves.
The heat exchange cell as claimed in claim 32, wherein each said groove is formed in a plate wall of a said first and/or second plate, and said plurality of projecting studs comprise indents within a said groove.
The heat exchange cell as claimed in claim 32 or 33, wherein said studs comprise substantially circular indents.
The heat exchange cell as claimed in any one of claims 32 to 34, wherein said studs have a substantially mesa shape.
The heat exchange cell as claimed in any one of claims 32 to 35, wherein said plurality of studs are arranged in a regular two-dimensional grid pattern in a plurality of rows and columns.
The heat exchange cell as claimed in any one of claims 32 to 36, wherein said plurality studs are arranged in a substantially rhomboid pattern.
The heat exchange cell as claimed in any one of claims 32 to 37, wherein said second plate is welded to said first plate around a perimeter of said second plate, to form a leak tight fluid containing chamber between said first and second plates.
The heat exchange cell as claimed in any one of claims 32 to 38, wherein said plurality of grooves extend approximately parallel to each other, and said first and second plates are joined together by welding between said grooves.
The heat exchange cell as claimed in any one of claims 32 to 39, comprising first and second liquid distribution regions located respective first and second ends of said cell, for channelling liquid from a liquid inlet or to a liquid outlet and to a plurality of liquid channels extending along said heat exchange cell, wherein a said liquid distribution region is designed to extend across a full depth of said cell so as to distribute liquid volume substantially evenly across said plurality of liquid channels.
The heat exchange cell as claimed in any one of claims 32 to 40, comprising one or more liquid distribution regions located at one or both ends of said cell, said liquid distribution regions each comprising a volume having a substantially constant internal width, between said first and second plates, and a substantially wedge or tapered area.
A gas to liquid heat exchanger as claimed in claim 1, comprising a plurality of heat exchange cells,
each said cell comprising an inner plate and an outer plate;
said plurality of heat exchange cells being stacked together side-by-side to form a plurality of gas passages there between;
each said cell having an outer surface comprising a plurality of protrusions which extend into said gas passages between said cells, for promoting turbulent gas flow between said cells.
The gas to liquid heat exchanger as claimed in claim 42, wherein said plurality of protrusions are arranged in a regular two-dimensional grid pattern in a plurality of rows and columns.
The gas to liquid heat exchanger as claimed in claim 42 or 43, wherein said plurality protrusions are arranged in a rhomboid pattern.
The gas to liquid heat exchanger as claimed in any one of claims 42 to 44, wherein said gas passages are bounded by first and second planes, each of which intersect respective outer walls of adjacent said cells at the position of a plurality of elongate liquid coolant channels, and wherein a distance between said first and second planes is no less than 2mm, except in regions where one or a plurality of studs are present.
The gas to liquid heat exchanger as claimed in any one of claims 42 to 45, characterised in that a liquid flow pattern of liquid flowing through the centres of said cells is independent of and decoupled from a gas flow pattern of gas flowing between said cells.
The gas to liquid heat exchanger as claimed in any one of claims 42 to 46, wherein said plurality of protrusions cause substantially teardrop shaped eddies in said gas flow.