NO843967L - HEAT EXCHANGE - Google Patents

Description

The background of the invention

1. The area of application

The present invention relates to heat exchangers of the plate/fin type as well as finned plates with an open surface which can be stacked on top of each other to form cross-flow heat exchangers.

2. Description of the state of the art

Heat exchangers of the plate/fin type are mainly built

up of channels and rib-shaped constructions. Heat exchangers of the counter-flow type can be obtained. However, providing a manifold that separates the fluids at the entrances and exits of the plate stacks becomes particularly complex in that case. Since the manifold in cross-flow heat exchangers without comparison

is simpler in structure, such a heat exchange system is more often used, this despite the fact that the cross-flow system is less efficient than the counter-flow system and that the cross-flow system introduces serious thermal and mechanical loads.

A counter-flow system which has attempted to solve the manifold problem with counter-flow heat exchangers is described in US Patent No. 3,305,010. This patent document describes a heat exchanger consisting of stacked plates and fin elements as well as a complex manifold arrangement for introducing fluids

with different temperatures into opposite ends of the assembly. However, US Patent No. 3,305,010 does not show a plate that serves as both a plate and a fin. Nor does this patent document show devices for internal branching on the plate in the plane of the plate.

Another counter-flow system is the Alfa-Laval system described

in "The Proceedings of the 5th OTEC Conference", Miami, Florida (February 1978) pages VI 288-320. The Alfa-Laval solution mainly consists of a stack of thin metal sheets, a frame and devices to hold the parts together. The plates are suspended between horizontally bearing rods at the top and bottom, and are pressed together against a stationary frame plate by means of tightening bolts and a movable pressure plate. The frame plate is equipped with nozzles for inlet and outlet connections. Each plate is sealed around the plate's circumference with a sealing ring and is

the putty in a compressed stack. The flow openings at each of the plate's corners are individually sealed and consequently divide the intermediate space into two systems for alternative flow channels. Two media pass through these, with the hotter medium emitting heat to the cooler by conduction through the thin plates. This sealing arrangement eliminates the risk of interleakage between the two media. The plate, which is the basic element according to this concept, has a corrugated pattern embossed on the plate. These corrugations can be arranged in an unlimited number of plates. The specific pattern is the result of a trade-off between pressure drop and convective heat transfer characteristics.

The sealing rings according to the Alfa-Laval system are cemented to the plates in compressed grooves and are generally made of elastic material such as natural rubber, nitrile, butyl, neoprene, viton, etc. The choice of material depends on the working conditions. However, it should be noted that the upper limits are around 360 PSI and around 400°F.

The present invention differs from the Alfa-Laval solution in many ways, including: (1) that the Alfa-Laval system depends on sealing rings, which limits the operating pressure and temperature; (2) that the Alfa-Laval system does not have contact fins or essentially flat plate bottoms to provide the necessary plate-to-plate contact to achieve an optimal heat transfer coefficient.

The requirements for gas/liquid coolers, such as e.g. air-to-oil or air-to-water generally requires a low pressure drop of about 0.5 psi in water on the air side and must also be suitable for fitting in areas such as the front of a car radiator where the maximum allowable depth is less than 1.5 inch. Furthermore, the efficiency requirement for these solutions is less than 50% so that cross-flow solutions as well as counter-flow solutions can be used. The latest solutions of a bent fin tube assembly and other solutions suffer from poor contact area with the liquid tubes and require control devices for the liquid speed on the liquid side to adapt the necessary convection conditions. Due to the need for soldering and brazing during manufacture, assembly of the previously known solutions is not suitable for automated mass production.

Purpose of the invention

An object of the present invention is to provide a one-piece internally branched fin plate for a heat exchanger of the plate/fin type.

A second object of the present invention is to provide an open-ended fin plate that can contain a plurality of fin configurations to thereby improve heat transfer through increased surface area and plate-to-plate contact.

A further object of the present invention is to provide a heat exchanger which has simplified manifolds.

A further object of the present invention is to provide a simple manifold suitable for an internally branched plate stack.

Another object of the present invention is to provide a cost-effective as well as an efficient cross-flow heat exchanger.

A further object of the present invention is to provide a heat exchanger which has plates which are relatively free from mechanical and thermal built-in stresses.

A further object of the present invention is to provide a heat exchanger which is cheap to manufacture.

Summary of the invention

The invention comprises a heat exchanger of a stacked plate/fin type, where two types of finned plates are used. The first plate which is preferably used to transfer liquids consists of an open-faced plate with a flat bottom and a top formed with an upwardly extending circumferential wall. Upwardly spaced apart fins are formed in the central part on the top side of the plate, as concave end regions are arranged between the fin regions and the peripheral wall to form internal manifolds. Openings are provided through the plate, with one opening passing through each manifold region. The channels between the fins extend in the area from one manifold region to the other. The height of the fins and the peripheral wall are equal, so that their top surfaces form a coplanar surface.

The second disc which is preferably used for transfer

of gases, consists of an open-faced plate with a flat bottom,

and located at a distance from each other fins in the central part on the top side of the plate. The end regions have top surfaces that have the same height as the top surface of the fins, so that a surface situated in the same plane is formed by the top surfaces of the fins and the end regions. An opening is formed transversely through the plate at each end region, so that said manifold openings coincide when said first and second plates are stacked on each other to form an inner, or conducting manifold. It is also advantageous if the plates complement each other by 180°, i.e. when one plate in the stack is azimuthally rotated 180° with respect to the others, its openings will still coincide with the openings in the remaining stack.

The top plate can be covered by a flat plate, with the bottom off

each plate serves as a cover for the plate below. The plates can, if desired, be mutually sealed or stapled together.

The fins and channels on said second plate are arranged in

a direction transverse to the direction of the fins and channels of said first plate.

The invention provides an efficient, simple and easy-to-manufacture, easy-to-assemble, and relatively inexpensive plate stack heat exchanger that does not require an external manifold if a liquid is to be air-cooled in it.

Other purposes, advantages and new features of the present invention will be apparent from the following detailed description of the invention seen in connection with the accompanying drawings.

Brief description of the drawings

Figure 1 shows an exploded, isometric elevation of a plate stack for a heat exchanger according to the present invention. Figure 2 shows an exploded isometric view of a plate stack with a different type of first plate. Figure 3 shows an isometric elevation of a cover plate.

Figure 4 schematically shows different shapes of fins

and channels that can be used according to the present invention. Figure 5 schematically shows a type of interrupted fin used according to the present invention.

Figure 6 shows a partial schematic illustration of a

type of fin that has a sinusoidal design.

Figure 7 shows a partial schematic illustration of a

type of fin that has a herringbone shape.

The same elements or parts in the different figures are indicated by the same reference numerals, while equivalent elements are marked.

Detailed description of preferred embodiments

Figure 1 shows an exploded stack 10 consisting of three plates 12, 14 and 12'. Two differently shaped plates 12 and 14 are used. The first plate 12 consists of an open-flatted plate equipped with a flat bottom 16. The top surface 17 of the plate 12 supports an upwardly projecting peripheral wall 18 which has a height h^. The central part of said first plate 12 supports a plurality of fins 20, preferably parallel fins, extending upwards and at a distance from each other, channels 22 being provided between the fins. The end region between the ends of the fins 20 and the end of the peripheral wall 26 forms a recess or cavity, which constitutes an inner manifold 24 through which a manifold opening 28 is bored. As shown, there is a manifold 24 and a manifold opening 28 at each end of the plate 12. The top surfaces of the fins 20 are also a height h above the bottom so that the top surface of the fins and the wall lie in the same plane. The channels 22 and the fins 20 are formed so that their axes extend substantially in the same direction as a line drawn between the manifold openings 28.

The second plate 14 is also equipped with an open-flat plate equipped with a flat bottom 34. The height of said second plate 14 between the bottom 3 4 and the top surface 3 6 is h^. h2 should preferably be greater than h^ if said first plate 12 is used for fluid flow, such as hot oil, while said second plate 14 is used for fluid flow such as cooling air. The central region of said second plate 14 also contains fins 20' and channels 22', the channels 22' extending downwardly from the top surface 36. The fins 20' and channels 22' are adjacent to the end regions 32, each of which is provided with a manifold opening extending transversely through the plate and such a location that the manifold openings 28, 28' coincide when the plates are stacked on top of each other, thereby forming internal manifolds in the stack. The flow of fluid through the manifold openings and grooves in said first plate is shown by means of arrows and lines labeled A, resp. B. The flow of fluid through the grooves in said second plate is shown by means of arrow marked C. One or both of said directions can be reversed if desired.

It should be stated that the plates 12 and 14 can each be azimuthally rotated 180° as the openings will still coincide. 180° rotatability can be maintained even if each opening in a plate is offset by the same distance but in the opposite direction from the longitudinal centerline of the plate. In that case, of course, this must be done on all the plates in a stack.

Figure 2 shows a second type of said first plate 38.

Here, the central region is comprised of fins 20" and channels 22", with two side fins 40 and 42 replacing the peripheral wall on each side of the plate 38. The end regions are flat, with the top-over tracks 44 lying below the top surfaces 30 of the fins 20".

and preferably in the same plane as the bottom of the channels. An end fence, in the form of a generally U-shaped portion 46, is placed on the surface 44 at each end region, to be matched at each end with corresponding ends of the side fins 40 and 42, thereby forming a dam around the periphery of the plate 38 , while an inner manifold 24' is formed at each end region. Manifold openings 28"

is arranged in the inner manifold region of each plate 38 intended to coincide with manifold openings 28' in said second plate 14 when the two types of plates are stacked on top of each other.

The dam parts 46 are fixedly mounted or otherwise sealed to the end regions to form an end fence. The bottom of said second plates 14 should also be sealed against the top of the underlying first plates 12 (or 38) to prevent leakage of fluids flowing through the channels 22" and the internal manifolds 24" of said first plates 12 (or 38). This can be achieved e.g. by brazing in a brazing mold with plate-to-plate brazing foils, or by means of seals. The seal between the bottom of said first plate 12 and the top of said second plate 14 is unnecessary if said second plate 14 is used for the transfer of a gas, but may be desirable to stabilize the stack 10.

Said first plates can be located below said

other plates.

The first plate 12 (Fig. 1) can e.g. be produced

by means of a blow extrusion process, in which the former presses the flat plate so that fins and the peripheral wall or frame are extruded into channels by means of the press.

The second plate 14 can be formed by means of an extrusion process, where the shaped press extrudes channels and fins in the central region.

Similarly, the damming plate 38 can be formed by extruding the fins over the entire area of the base plate and then machining away the fins at the end region of the plate to thereby provide end surfaces on which the damming parts can be placed to form end fences.

Figure 3 shows a single plate which can be used as a cover plate 48 on the stack 10. The cover plate 48 can be attached to or bolted to the stack 10. The cover plate and the corresponding bottom plate can be equipped with projecting surfaces equipped with holes for bolts or grooves for bolting together the complete stack assembly. The top plate or the bottom plate or both plates may be equipped with inlet and outlet openings for the plate stack assembly.

The fins 20, 20' and the channels 22, 22' can have different cross-sectional shapes as shown in Figure 4. The conventional channel and fin type with sharp corners is represented by the reference number 50. However, channels with rounded corners 52, U-shaped channels 54, V-shaped channels 56, trapezoidal channels 58, etc. are also used without thereby deviating from the invention. In addition, fins 60 can be interrupted, e.g. as shown in Figure 5, is used. The channels can also have different widths on one and the same plate. In addition, the fins 20, 20' may also have a meandering shape 62 (Figure 6) or other non-rectilinear configurations as shown using the herringbone configuration in Figure 7.

It is obvious that many modifications and variations

of the present invention is possible in light of the above description. It should therefore be noted that the present invention can be practiced in other ways than those described above.

Claims (10)

1. A plate stack assembly for a heat exchanger comprising: at least a first plate having a flat bottom and a raised circumferential wall on the top side of the plate, as well as raised and spaced apart fins in the central region of the plate on the top side for forming intermediate channels, the height of the peripheral wall and the fins being identical and where the plate at opposite ends has internal manifold regions between said fins and the peripheral wall, each manifold region being equipped with a manifold opening that extends from the top to the bottom of said plate and where the axes of the fins extend substantially in the same direction as a line connecting said manifold openings; and at least a second plate of the same shape and dimensions as said first plate, except in the direction transverse to the plane of the plate, which second plate has a flat bottom and upwardly spaced apart fins in the central region of the top side for forming of channels and with mutually facing end regions whose height is identical to the height of said fins, which end regions are equipped with a continuous manifold opening which coincides with the manifold openings at each end of said first plate, and where the axes of the fins are essentially located across of a line between the manifold openings, so that when said first and second plates are stacked on each other, the manifold openings will coincide to form a different transverse manifold at each end and the bottom of one plate is in contact with the upper edge of the fins of the underlying second plate to form closed channels in said second plate, so that the flow of fluids through the plates is thereby cross-flow. 2. Assembly as stated in claim 1, which assembly includes a cover plate of the same dimensions as the other plates, except in a direction transverse to the plane of the plates for covering the top of the top plate. 3. Compilation as stated in claim 1, where said plate stack assembly consists of a plurality of first plates and a plurality of said second plates. 4. Compilation as stated in claim 1, where the upstanding peripheral wall extends only along both sides of said central region of said first plate, said assembly further including dam parts extending along the wall-free portions of said first plate between the circumferentially situated walls on each side of the plate to thereby form an internal manifold region at each end, the height of said dam parts being such that their top surfaces lie in the same plane as the top surfaces of the fins when the dam parts are in place on said first plate. 5. Compilation as stated in claim 2, where the fins on said first and said second plate form parallel channels. 6. Compilation as stated in claim 4, where said dam parts are anchored to said first plate, and that the plates are fixed together. 7. Plate for a plate stack assembly on a heat exchanger comprising: a plate having a flat bottom and an upstanding wall on the top side of the plate, which wall extends along the periphery of the top side and has upstanding, spaced apart fins arranged in the central region for forming intermediate channels, the height of the peripheral wall and the fins are identical, and where the plates have opposing internal manifold regions at each end, located between said fins and the peripheral wall, each manifold region being equipped with a manifold opening that extends through the plate from top to bottom, while the axes of the fins essentially is coincident with the direction of a line extending between the manifold openings. 8. Plate as specified in claim 7, where said upstanding peripheral wall extends only along both sides of said central region of said plate, and wherein said plate further includes dam portions extending along the wall-free portion of the plate between the peripheral walls on each side to thereby form an internal manifold region at each end, the height of said dam parts being such that their top surfaces lie in the same plane as the top surfaces of the fins when the dam parts are placed on the plate. 9. Plate for a plate stack assembly in a heat exchanger, comprising: a plate having a flat bottom and upwardly projecting, spaced apart fins arranged on the central region on the top side of the plate for forming intermediate channels, which plate is provided with end regions whose height is identical to the height of said fins, said end regions being equipped with a manifold opening which extends through this, and where the top surfaces of said fins and end regions lie in the same plane, but where the axes of the fins essentially lie across an imaginary line between the manifold openings. 10. Plate as stated in claim 9, where said fins have an essentially rectangular cross-section.