GB2132748A - Improvements relating to heat exchangers - Google Patents

Abstract

A heat exchanger comprises a series of thermally conductive metal plates (A, B) which are interleaved or stacked to provide a plurality of alternate passages for respective fluids. Each plate (A, B) has a series of integral corrugations (10), formed as a plurality of spaced bands (9) extending laterally of the intended fluid flow direction, and between adjacent bands (9) there is disposed on one side of the plate at least one corrugated strip (12) which defines with the underlying and overlying plane parts of the plates a plurality of intervening flow passages which are of individually smaller cross-section and laterally offset in relation to the adjacent flow channels formed by the aforesaid integral corrugations (10). Gaps (g) exist between adjacent corrugations and the flow directions of different fluids-e.g. water and air-are indicated by respective arrows (W), (G). <IMAGE>

Description

SPECIFICATION Improvements relating to heat exchangers This invention relates to heat exchangers of the kind comprising a series of primary heat elements in the form of thermally conductive metal plates which are interleaved or stacked to provide a plurality of alternate passages for respective ones of two fluids, each plate having a series of integral corrngationsdefining a median plane of the plate, to opposite sides of which plane alternate half waves of the corrugations project. One such heat exchanger is disclosed in my British Patent Specification 1048122.

Such heat exchangers have many applications particularly when one fluid is a gas such as air and the other fluid is a liquid such as water, lubricating oil or fuel oil. One such application is in aerospace machines for cooling air with fuel whilst another is as a socalled intercooler in turbo charged diesel engines for the cooling of combustion air by water flow.

In the design of such heat exchangers it has now been realised that it is essential to break up laminar fluid flow, otherwise the heat exchanger has to have larger dimensions and it is to this end, with a view to providing a particularly compact and efficient heat exchanger that the present invention has been devised.

According to the invention, a heat exchanger of the kind referred to, is characterised in that the series of corrugations is formed as a plurality of spaced bands extending laterally of the intended fluid flow direction and that between adjacent bands there is disposed on one side of the plate at least one corrugated strip which defines with the underlying and overlying plane parts of the plates, a plurality of intervening flow passages which are of individually smaller cross-section and laterally offset in relation to the adjacent flow channels formed by the aforesaid plate corrugations, there preferably being a gap between each said strip and said plate corrugations.

Preferably two or more such corrugated strips are provided between each band with the corrugations of one such strip laterally offset with respect of those of the adjacent strip, as well as to those of the main corrugations of the plates.

Preferably also each plate will have a corrugated plate at each end for the guidance of fluid into and out of the flow passages, these end plates also forming with the underlying or overlying plane parts of adjacent plates a plurality of flow passages which permit heat exchange. Adjacent plates preferably have the corrugations of these end plates extending respectively longitudinally and transversely thereof corresponding to the directions of inlet and outlet of the respective fluids between which heat is exchanged.

These and other features of the invention should become more clearly apparent from the following description of a preferred heat exchanger as illustrated in the accompanying drawings in which: Figure 1 is a schematic drawing to illustrate the components and mode of fabrication of a first heat exchanger plate "A"; Figure 2, comparable to Fig. 1, illustrates the components and mode of fabrication of a second heat exchanger plate "B"; Figure 3 is an exploded view of the four outermost plates at the top or bottom of the heat exchanger; Figure 4 is a fragmentary perspective view of the heat exchanger; Figure 5 is a section on line V-V of Fig. 4; and Figure 6 is a general view of a complete heat exchanger to be used as an intercooler in a diesel engine turbocharger installation.

Referring now to the drawings (Fig. 6) the heat exchanger to be described essentially comprises a casing 1 with an air inlet 2, an air outlet 3, a water inlet 4, and a water outlet 5. This casing contains (Figs. 3 and 4) a brazed-together assembly of stacked or interleaved plates. These plates are of four kinds that it is to say upper and lower flat base plates 6, upper and lower apertured plates 7 which are next to the base plates and a plurality of corrugated plates "A" and "B" of closely related structure which are stacked alternately upon one another between the upper and lower apertured plates.

Fig. 1 shows, from top to bottom, successive stages in the manufacture of an "A" plate. Thus a rectangular steel plate 8 of minimum thickness is embossed with a series of six spaced parallel bands 9 of integral corrugations 10. These bands extend transversely of the plate at an angle of about 70 to the longitudinal axis of the plate. The corrugations 10 have their axes parallel to the side edges of the plate and define a median line of the plate 8 with alternate half waves of the corrugations projecting to opposite sides of this plane. The profile of these corrugations 10 is most clearly shown in Fig. 4. Thereafter two L-shaped spacer strips 11 are brazed to the margin of the plate 8.Then there is spot welded to the same face of the plate a series of narrow corrugated stainless steel strips 1 2 and corrugated substantially triangular fluid entry and exit strips 1 3. As can be seen from the bottom of Fig. 1 and also from Figs. 3 and 4 the corrugated strips 1 2 are attached to the plate in pairs along the spaces between the bands 9 of the embossed corrugations 10.

Each corrugated strip 1 2 defines with the underlying part of the plate 8-and with another plate stacked upon it-a plurality of intervening flow passages which are of smaller cross-section and laterally offset in relation to the flow passages defined by the corrugations 10. Also the corrugated strips of each pair have their corrugations offset in relation to one another. It should also be noted that there are small gaps between the strips 1 2 themselves, between the strips 1 2 and the embossed corrugations 10, and between the corrugations 10 and the inlet and outlet plates 13 and 15.

Fig. 2 shows in an analogous manner the mode of fabrication of a "B" plate which is essentially the same as for an "A" plate except for the substitution of two straight spacer strips 14 and two substantially triangular fluid entry and exit plates 1 5 of which the corrugations extend longitudinally relative to the underlying plate 8.

As shown in principle in Figs. 3 and 4 the heat exchanger body is comprised of a stack of alternately disposed "A" and "B" plates constructed as aforesaid with an apertured plate 7 and a base plate 6 disposed at both the top and bottom of the stack. When thus disposed in the present instance, the "A" plates accommodate air flow whilst the "B" plates accommodate water flow.

In Fig. 4, the arrows W indicate the directions of inlet and outlet of water whilst arrows G indicate the directions of inlet and outlet of air. Fig. 4 also indicates the offset or staggering both of the flow passages formed by adjacent pairs of strips 1 2 relative to one another and also the offset or staggering of those flow passages relative to the passages formed between the embossed corrugations 10 of adjacent plates.

tig. 4 also shows the gaps g between the corrugations 10 and the corrugated strips 12, between the strips 1 2 themselves and between one band 9 of corrugations 10 and an air outlet plate 1 5.

Typically the plates may be about 22 cms in length and 11 cms wide; each band 11 would then be about 1 5 mm wide and each strip would be about 7 mm wide. The overall depth of the stacked plates would be about 12 cms. A typical width for each gap g would be 1.6 mm that is to say the same as the hydraulic mean equivalent diameter but alternative widths could be 2 mm, 1.15 mm or 75 mm.

When the stack of alternately disposed plates A and B, together with plates 6 and 7 at top and bottom has been built up, the whole assembly is placed in a brazing furnace so that by reason of the copper plating on the strips 1 2 and spacers 11 and 1 2 the plates become brazed together. Finally the casing I is built around the stack.

Reduction of laminar flow of fluid in the heat exchanger is achieved because when fluid enters the gaps g between the embossed corrugations 10 and (a) the triangular plates 1 5 and (b) the strips 12, as well as the gaps between pairs of strips, turbulence is created due to the change in available total flow space. This laminar flow breakdown is increased still further by reason of the offset or staggering of the different rows of corrugations.

On test a heat exchanger similar to the one above described has been found to be extremely efficient when used as an intercooler of combustion air in a turbo-charged diesel engine, being capable of achieving a maximum air temperature drop of 11 7'C to ambient temperature.

However it is not always desirable to have such a highly efficient intercooler especially when the engine is running at part load, that is to say 50% or less, and additionally in extremely cold conditions.

Consequently the performance of this heat exchanger can be made infinitely variable by incorporating a thermostatically or electrically controlled by-pass valve system on the cooling fluid being fed into the heat exchanger to cool the engine inlet air.

As an alternative to stainless steel, the plates and indeed the whole assembly--can be made of any other high thermal conductivity metal or alloy such as for instance copper, aluminium or carbon steel and variations in performance can be achieved by varying the length of the fluid flow path between the plates, adjusting the number and spacing of the bands of embossed corrugations, the number of intervening corrugated strips, the number and size of the corrugations and thereby the total cross-sectional area of all the flow passages.

Whilst a rectangular heat exchanger unit has been described it is to be understood that it may be made of hexagonal, or other shape, in the first instance or by attachment of another one or more rectangular or other shaped original units.

In addition to the already mentioned advantages of high thermal efficiency and compactness, the heat exchanger also has the advantages of providing a large flow surface area and a large frontal area. Another advantage is that of the infinitely variable performance for part load conditions. Also the design of the heat exchanger allows its size to be varied to suit any required application.

Claims (4)

1. A heat exchanger of the kind referred to, characterised in that the series of integral plate corrugations is formed as a plurality of spaced bands extending laterally of the intended fluid flow direction and that between adjacent bands there is disposed on one side of the plate at least one corrugated strip which defines with the underlying and overly ing plane parts of the plates a plurality of intervening flow passages which are individually of smaller cross-section and laterally offset in relation to the adjacent flow channels formed by the aforesaid integral plate corrugations.

2. A heat exchanger in accordance with claim 1 in which there is a gap between each said strip and said plate corrugations.

3. A heat exchanger in accordance with claim 1 or 2 in which there are two or more such corrugated strips between each band with the corrugations of one such strip laterally offset with respect to those of the adjacent strip as well as to those of the aforesaid integral plate corrugations and there being a gap between each adjacent corrugated strip.

4. A heat exchanger constructed substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.