US3804162A

US3804162A - Heat exhanger

Info

Publication number: US3804162A
Application number: US00290639A
Authority: US
Inventors: S Kugler; S Bruzzi
Original assignee: British Oxigen Ltd
Current assignee: BOC Group Ltd
Priority date: 1971-09-21
Filing date: 1972-09-20
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16
Also published as: JPS4838554A; AU4692272A; AU470944B2; NL7212757A; FR2157804A1; GB1412100A; DE2245849A1

Abstract

A perforated plate heat exchanger comprising inlets and outlets for the gas streams to be heat exchanged and a plurality of heat conductive perforated plates arranged alternately with a plurality of heat insulative gaskets, whereby heat transfer takes place across the plates normally to the gas flow. Each gasket has a configuration of walls that defines a number of passages for each gas stream, interconnection between different passages of the same gas stream being given by walls of a complementary configuration in at least two neighbouring gaskets.

Description

[4 1 Apr. 16, 1974 HEAT EXHANGER Inventors: Simon Kugler, Barnet; Stefano Bruzzi, London, both of England Assignee: The British Oxygen Company Limited, London, England Filed: Sept. 20, 1972 Appl. No.: 290,639

3,477,504 11/1969 Colyer et a1. 165/164 Primary ExaminerCharles J. Myhre Assistant Examiner-Theophil W. Streule, Jr. Attorney, Agent, or FirmDennison, Dennison, Townshend & Meserole [5 7] ABSTRACT A perforated plate heat exchanger comprising inlets and outlets for the gas streams to be heat exchanged [30] Foreign Application P i it D t and a plurality of heat conductive perforated plates Sept 21 1971 Great Britain 43946/71 arranged alternately with a plurality of heat insulative Sept. 21 1971 Great 43947 71 gaskets whereby heat transfer takes Place across the plates normally to the gas flow. [52] U.S. Cl. 165/164 Each gasket has a configuration of walls that defines a [51] Int. Cl. F28d 9/00 number of passages for each gas stream, [58] Field of Search 165/135, 154, 164 interconnection between different passages of the same gas stream being given by walls of a [56] References Cited complementary configuration in at least two UNITED STATES PATENTS neighbouring gaskets- 3,534,813 10/1970 Fleming 165/164 9 Claims, 8 Drawing Figures I 1 1 i5? fih new 48' F 5 6 F mf 68 J lfl i BF Ali--62 50 l Fl 1 lil Jl :5 u il m if j-d E 52 -52 5 2 JY jslflw 54k 50 ]FH JI H 62 j i 1 cat J EL Q l5-6e' 56- F 1W 161 1 r 4 J[ u 41W fi-72 r Q J EB: I 4'8 42 44 7o PATENTEDAPR 16 I974 SHEET 1 [IF 5 L704.-. om 00000000 000000 PATENTEDAPR I6 197:

SHEET l [1F 5 HEAT EXHANGER This invention relates to a heat exchanger, in particular to a perforated plate heat exchanger.

A perforated plate heat exchanger is constructed from a plurality of perforated heat conductive plates which are arranged alternately with insulating gaskets. In operation two or more gas streams are arranged to flow through the perforations of the plates, being prevented from mixing by suitable arrangement of the gaskets. Transfer of heat from one stream to another occurs by heat conduction across the plates. An advantage of a perforated plate heat exchanger is that a large effective heat exchange area can be accomodated in a small volume. Thus a perforated plate heat exchanger can be made of considerably smaller size than a conventional heat exchanger required to perform the same duty. For cryogenic applications in particular, this can lead to considerable reduction in the size and hence cost of the cold box required to insulate the heat exchanger. This in turn leads to a cold box of greater insulative efficiency.

Despite their considerable advantages over the conventional type of heat exchanger, the perforated plate heat exchangers available hitherto have not achieved the theoretically possible levels of efficiency and have not attained the commercial success that their concept merits.

In most applications the heat exchanger is designed to effect heat exchange between two gas streams, one a high pressure stream and the other a low pressure stream. Each stream enters the heat exchanger through a header which divides the gas stream into a number of substreams in accordance with the number of passages in each gasket.

In known forms of perforated plate heat exchanger the gasket is designed with passages for alternate high pressure and low pressure substreams. This arrangement facilitates good heat transfer between the high and low pressures streams. In these forms the gaskets are designed and juxtaposed to permit communication between passages through which different substreams of a particular gas flow. Such communication also facilitates good heat transfer by maintaining an even pressure drop across the heatexchanger for a given gas, and thus promoting good flow distribution.

Generally this form of gasket comprises a frame and a series of narrow walls which are integral with and located within the frame, and which define the passages for gas streams passing through the heat exchanger.

The walls extend longitudinally from and to end of the frame to form the passages, or if the gasket is of circular cross-section they are located concentrically within the frame. With these arrangements however, communication between different passages through which a particular gas stream flows cannot be achieved.

One known form of gasket which enables such communication includes a rectangular frame and one or more substantially U-shaped members within the frame and extending across it. This form of construction is known as fingering and is described in U.S. Pat. specification No. 3,477,504. The U-shaped members divide the area within the frame into inter-communicating passages within the U-shapes for one gas stream and inter-communicating passages outside the U-shapes for a second gas stream. This form of gasket has the disadvantage, particularly if provided with a large number of U-shapes, that it is of flimsy structure and consequently prone to damage in handling and construction and, in assembling the heat exchanger, can easily be misaligned with respect to the other gaskets. In order to make a gasket of such a configuration but sufficiently robust it needs to be undesirably thick or of an undesirably small size.

This invention relates to a form of heat exchanger whereby interconnection of different passages of the same gas stream can be achieved whilst avoiding the flimsiness introduced by fingering.

Accordingly the invention provides a heat exchanger including a plurality of perforated heat conductive plates arranged alternately with a plurality of heat insulative gaskets, and inlets to and outlets from, the heat exchanger for at least two separate streams of gas to be heat exchanged, wherein each gasket has a configuration of walls that defines a plurality of passages for each gas stream, and wherein interconnection between different passages of the same gas steam is provided by walls of a complementary configuration in at least two neighbouring gaskets.

Each gasket has preferably a configuration of walls that defines separated passages for the same gas stream, whereby interconnection of different passages for the same gas stream is achieved by neighbouring gaskets only. This enables a relatively stiff gasket to be made, and so facilitates manipulation of the gaskets during assembly of the heat exchanger.

Each gasket is preferably of identical configuration, interconnection between different passages for the same gas stream being effected by the location of at least one of the gaskets in an inverted attitude with respect to a neighbouring gasket.

A preferred form of gasket according to this invention includes a rectangular frame, the walls of the gasket extending within, and being intergral with, the frame and defining the passages for the gas streams. In this form of gasket several of the walls defining the passages can extend directly between two sides of the frame so as to give a relatively stiff structure. Thus each gasket may include a first set of walls parallel to the longer sides of the frame and extending directly between the shorter sides, and a second set of walls parallel to and-inerjacent with the first set, at least some of the second set of walls being joined at both ends to different walls of thefirst set by transverse walls to form passages each having an enlarged end portion, the passages apart from the enlarged end portions being disposed in mirror symmetrical relationship with respect to a plane bisecting the shorter sides of the frame, whereby interconnection between different passages for the same gas stream is by overlap of the enlarged end portions of at least one gasket and a neighbouring inverted gasket.

Preferably the gasket includes one or more stiffening strips integral with the parallel walls of the gasket and extending transversely between, and integral with, the longer sides of the frame. In order to avoid the creation of intermediate passages having no intercommunication with similar intermediate passages in the other gaskets, the or each stiffening strip should be asymmetrical with respect to an axis bisecting the shorter sides. The stiffening strips help to stiffen a relatively long gasket.

In accordance with standard practice for heat exchanger design the gaskets can be designed to provide alternate relatively narrow and relatively wide passages for the high pressure and low pressure streams respectively. It is an advantage of the heat exchanger of this invention that the relative widths of the high and low pressure passages can be chosen to give the desired pressure drops for the gas streams.

For reasons connected with the pressure distribution across the heat exchanger it is preferred that the two outer passages take low pressure gas.

Preferably the gaskets are located with several sequences of gaskets, each in an inverted attitude with respect to a neighbouring sequence. This arrangement reduces the pressure drop that would occur during flow redistribution with the inverted and uninverted gaskets arranged alternately.

It has been found that the optimum parameters for the heat exchanger of this invention are as follows:

a. the cross-sectional area of each perforation is in the range of 4 to 12.5 X in b. the thickness of each plate is in the range 1.0 to 2.0

X 10 in;

c. the total area of perforations in each plate is in the range 25 to 40 percent of the area defined by the periphery of the plate;

d. the thickness of each gasket is in the range 0.5 to

1.0 X 10 in;

e. the width of each wall of the gasket is in the range 1.0 to 1.5 X 10 in; and

f. the aspect ratio of each gasket and each plate is in the range 1.5: l to 3:1.

The gas streams may be introduced into and leave the heat exchanger by means of headers. Although the headers may be located at the side of the heat exchanger, they are preferably located at either end generally parallel to the plates.

The heat exchanger according to this invention is particularly suitable for use in cooling a gas to cryogenic temperatures. For instance in a typical construction about 500 plates may be required to cool high pressure helium from 300K to 80K with low pressure helium flowing countercurrently from 75K to 295K.

An appropriate choice of materials for the construction of the componenets of the heat exchange is important to its performance. For use at cryogenic temperatures the perforated plates are preferably of aluminium, the gaskets of a non-metallic material, for example a material based on cellulose fibre or glass fibre, and the gaskets sealed to the plates by means of an adhesive which withstands thermal cycling between ambient and the desired low temperatures. If on the other hand the heat exchanger is required to cool a inlet stream having a temperature greater than about 450K and adhesive cannot be used. Thus for such use the perforated plates are preferably of high conductivity, for example copper, and the gaskets are preferably of comparatively low conductivity, for example stainless steel, the gaskets and perforated plates being sealed together by brazing.

The perforations in the plates may be formed by punching or solvent etching and the gaskets may be made to the desired configuration by cutting with a forme or by a laser cutting method. Laser cutting is a particularly suitable method for slotting the wooden base of a forme required to cut a complex gasket from a non-metallic material.

Desirably the componenets of the header are formed from aluminium. Alternatively the header may be made of one piece by casting.

Desirably jigs are used in assembling the heat exchanger to facilitate alignment of the gaskets with the perforated plates, and to apply adequate pressure during curing.

When the plate and gaskets have been assembled and the headers fixed in position, clamping means, for example, tie-bolts, may be applied about the ends of the heat exchanger. This aids in preventing the seals between the perforated plates and the gaskets from being broken by, for example, internal pressure within the heat exchanger. Desirably the clamping means is prestressed, for example by means of springs formed from a stack of Belville washers. This enables the clamping means to adjust to thermal expansion or contraction during operation of the heat exchanger.

The present invention is now described by way of example, with reference to the accompanying drawings,

of which:

FIG. 1 is a perspective view of a perforated plate heat exchanger according to this invention,

FIG. 2 is a plan view of a portion of a perforated plate used in the heat exchanger shown in FIG. 1.

FIG. 3 is a plan view of a gasket used in the heat exchanger shown in FIG. 1;

FIG. 4 is a plan view of two superimposed gaskets of the form shown in FIG. 3, one gasket being inverted with respect to the other and the intervening plate being omitted for purposes of clarity.

FIG. 5 is a section through the line A-A' in FIG. 1.

FIG. 6 is an elevation of a header used in the heat exchanger shown in FIG. 1;

FIG. 7 is a section through the line 8-3 in FIG. 6; and

FIG. 8 is a section through the line C-C in FIG. 6.

The heat exchanger shown in FIG. 1 is formed from a plurality of rectangular perforated aluminium plates separated from each other by insulating gaskets. Each gasket 4 is bonded between a pair of the plates 2 by means of an epoxy adhesive. Thus a rigid structure of alternate plates and gaskets is formed. The heat exchanger also includes at its ends headers 8 and 10 which are identical in construction. The header 8 has an inlet pipe 12 for a first gas stream and the header 10 has an inlet pipe 14 for a second gas stream. Thus the gas streams pass countercurrently through the heat exchanger, the first gas stream leaving the heat exchanger, through an outlet pipe 16 of the header l0, and the second gas stream through an outlet pipe 18 of the header 8.

The form of perforated aluminium plate used in the heat exchanger is shown in FIG. 2. It has equidistant rows of circular perforations 20. The holes are arranged such that an equilateral triangle is formed between a hole in one row and two adjacent holes in an adjacent row. Fabrication by normal methods and to normal standards of accuracy, ensures random misalignment between the holes in adjacent plates after assembly. Each plate has a thickness of 1.48 X l0 in (3.76 X l0 m, 2.8 SWG) and each perforation a diameter of 3.1 X 10 in (7.9 X 10 m). Each plate has a length of 18 in (0.46m) and a width of 7in (0.18m) and has an average 408 perforations per square inch.

The form of gasket used in the heat exchanger is shown in FIG. 3. It has a length of 18 in (0.46m) and width of 70in (0.18m) and includes a rectangular frame 22, the longer sides of which are indicated by the

references

24 and 26, and the shorter sides by the

references

28 and 30.

Extending directly between and integral with the

sides

28 and 30 of the frame, and parallel to the

sides

24 and 26, are six walls indicated by the reference numeral 32. Located between and parallel to each pair of the walls 32 are walls 34. A wall 36 is located between and is parallel to the side 26 of the frame 22 and the nearest of the walls 32 thereto. Each of the walls 34 is shorter than the walls 32, and each is connected between a pair of the walls 32 by connecting

walls

38 and 40 extending normally therebetween. Each of the connecting walls 38 extends from a wall 32 at a region proximate to the side 30 of the frame 22 and joins a wall 34 at the end thereof. In like manner, each of the connecting walls 40 extends from a wall 32 at a region proximate to the side 28 of the frame 22 and joins a wall 34 at the end thereof. The connecting walls 38 are shorter than the connecting walls 40 so that the

walls

34 and 36 define two sets ofv passages of different widths.

The wall 36 terminates at one end in the side 28 of the frame and at its other end in a wall 42 which is equal in length to each of the walls 38 and which extends normally from the walls 36 and joins the nearest thereto of the walls 32 at a region proximate to the side 30 of the frame.

Extending between the

sides

24 and 26 of the frame are staggered stiffening strips 44 and 46. These are equally spaced between the

sides

28 and 30 of the frame and are integral with the

walls

32, 34 and 36. The

parallel walls

32 and 34, the connecting

walls

38 and 40, and the

sides

28 and 30 of the frame define a series of ten generally rectangular passages each of which has a projecting end portion. It can be seen that these passages are generally L-shaped. Five of the gassages are defined between each wall 32, each wall 34, each wall 40 and the side 28 of the frame 22 and are intended for a high pressure gas stream. They are disposed in alternation with the five passages defined between each wall 32, each wall 34, and each wall 38 and the side 30 of the frame 22, and are intended for low pressure gas. The five high pressure passages are indicated in sequence from the side 24 to the side 26 of the frame, by the

references

48, 50, 52, 54, and 56 and the five low pressure passages are similarly indicated by the

references

60, 62, 64, 66 and 68. The high pressure passages are of shorter width than the low pressure passages as each connecting wall 38 is shorter than each connecting wall 40.

It can be seen that the gasket includes three further passages located between the

sides

24 and 26 of the frame and the passages 48 to 68. Thus a rectangular passage 70 is defined between the side 24 of the frame 22, the nearest thereto of the walls 32 and the

sides

28 and 30 of the frame 22. The passage 70 is intended for low pressure gas. A further passage 72 for low pressure gas is defined between the

sides

26, 28 and 30 of the frame 22, the wall 36, the wall 42, and the right-hand end (as viewed) of the nearest to the side 26 of the walls 32.

This passage is generally rectangular having a projecting end portion located adjacent to the side 30 of the frame 22. A sixth high pressure passage indicated by the reference 74 is defined between the wall 36, the wall 42, the side 28 of the frame 22, and is rectangular having the same width as the other high pressure passages.

Each of the

low pressure passages

60, 62, 64, 66 and 68 has a general width of 14mm. and the passages and 72 a general width of 7mm. Each of the

high pressure passages

48, 50, 52, 54, 56 and 74 has a general width of 5mm. The width of the projecting end portion of each of the

passages

48, 50, 52, 54, 56, 60, 62, 64, 66 and 68 is 22mm and the width of the projecting end portion of the passage 72 is 15mm. Neither of the

passages

70 and 74 has a projecting end portion.

All of the

walls

32, 34, 36, 38, 40 and 42, and the

strips

44 and 46 have a width of 3mm; each of the

sides

24 and 26 of the frame has a width of 14.0mm; and each of the sides 28 and 30 a length of 10mm. The gasket thus covers 36 percent of the surface area of a plate in the heat exchanger, 19 percent of which is covered by the frame and 17 percent of which is converted by the walls and the stiffening strips.

Each gasket is formed from a single piece of glassfibre mat by use of a forme made by a laser cutting technique.

FIG. 4 illustrates the manner in which the projecting end portions of the passages of the gaskets enable intercommunication between different passages of the same gas stream. In FIG. 4 two gaskets of the form depicted in, and as described with respect to, FIG. 3 are shown, one located above the other. Each rectangular major portion of each passage in the upper (as shown) of the gaskets coincides exactly with a rectangular major portion of a passage in the lower gasket. The intercommunication is achieved by means of the projecting end portions of the passages. Considering the high pressure passages it can be seen that the end portion of the passage 48 in the upper gasket communicates with the end portion of the passage 56' of the lower gasket. Similarly the end portion of the passage 50 of the upper gasket communicates with the end portion of the passage 54 of the lower gasket, and the end portion of the passage 52 of the upper gasket overlaps with the end portion of the passage 52 of the lower gasket and so With the low pressure passages the end portion of the passage 72 of the upper gasket communicates with the end portion of the passage 60' of the lower gasket; the end portion 68 of the upper gasket communicates with the end portion of the passage 62 of the lower gasket, and similarly the end portions of the

passages

66, 64, 62 and 60 of the upper gasket communicates with the end portions of the

passages

64, 66', 68' and 72 of the lower gasket.

As the stiffening strips 44 and 46 of the upper and lower gaskets are not coincident they do not hinder intercommunication between different portions of the same channel.

In the heat exchanger the gaskets are located such that, proceeding through the heat exchanger, five successive gaskets are in the attitude of the upper (as shown) of the gaskets in FIG. 4 and the next five gaskets are in the attitude as shown of the lower of the gaskets in FIG. 4. It is desirable to form the gaskets having index marks joined on their frames, so that during assembly of the heat exchanger the attitude of a gasket can be determined by reference thereto.

The construction of the header 8 of the heat exchanger is shown in FIGS. 6 to 8. The

pipes

12 and 18 are welded to

caps

84 and 86. The

caps

84 and 86 are welded to a thick aluminium header plate 82 which has six passages 90 of equal width for high pressure gas, and seven passages 92 for low pressure gas. The

passages

90 and 92 coincide with corresponding passages in an adjacent gasket. The header plate 82 also has several holes 88 formed near its periphery to enable clamps to be fitted.

The high pressure passages 90 are formed such that they extend through the header plate 82 in the path thereof that cooperates with the cap 84, but only a part of the way through the other half thereof that cooperates with the cap 86. Similarly the low pressure passages 92 are formed that such that they extend through the header plate in the half that cooperates with the cap 86, but only a part of the way through the half thereof that cooperates with the cap 84.

Thus high pressure gas entering the heat exchanger through the pipe 12 is able to pass along the high pressure passages 90 only but is able to flow along the full extent of these passages. Similarly the low pressure gas leaving the heat exchanger through the pipe 18 is only able to enter the pipe 18 from the low pressure gas passages 92 but is able to flow along the full extent of these passages.

The header is identical to the header 8. Both headers are bonded to gaskets.

Referring again to FIG. 1 of the drawings, the heat exchanger includes 525 of the perforated plates interjacent with 526 gaskets. The total extent of the heat exchanger from header to header is 12 in (0.13m).

It is found that the heat exchanger may be operated between a temperature range of 80 to 300K, with a helium gas flow rate forboth high pressure and low pressure streams of 20 g s with a heat transfer efficiency of more than 97 percent, and with a high pressure stream inlet pressure of 40 atm and a low pressure stream inlet pressure of 1.1 atm.

What we claim is:

1. A heat exchanger comprising a plurality of perforated heat conductive plates, a plurality of heat insulative gaskets alternately arranged successively with respective ones of said plurality of perforated heat conductive plates, means forming an inlet for each of a first and second gas stream passing concurrently through said heat exchanger, means forming an outlet for each of said first and second gas streams leaving said heat exchanger, each said gas stream having a different pressure than the other, said heat insulative gaskets having a configuration of walls formed therein defining a plurality of passages for each gas stream and means including said walls formed by said gaskets interconnecting the passages of each gas stream, said last mentioned means being constituted by walls of complementary configuration in at least two neighboring gaskets.

2. A heat exchanger as claimed in claim 1, in which each gasket has a configuration of walls that defines separated passages for the same gas stream, whereby interconnection of different passages for the same gas stream is achieved by neighbouring gaskets only.

3. A heat exchanger as claim in claim 1, in which each gasket is of identical configuration, interconnection between different gas passages for the same gas stream being effected by the location of at least one of the gaskets in an inverted attitude with respect to a neighbouring gasket.

4. A heat exchanger as claimed in claim 3, in which each gasket includes a rectangular frame, the walls of the gasket extending within, and being integral with, the frame.

5. A heat exchanger as claimed in claim 4, in which each gasket has several of its walls extending directly between two sides of the frame so as to give a relatively stiff structure for each gasket.

6. A heat exchanger as claimed in claim 5, in which each gasket has a first set of walls parallel to the longer sides of the frame and extending directly between the shorter sides, and a second set of walls parallel to and interjacent with the first, at least some of the second set of walls being joined at both ends to different walls of the first set by transverse walls to form passages each having an enlarged end portion, the passages, apart from their end portions, being disposed in mirror symmetrical relationship with respect to a plane bisecting the shorter sides of the frame, whereby interconnection between different passages for the same stream is by overlap of the enlarged end portions of at least one gasket and a neighbouring gasket which is inverted with respect to said at least one gasket.

7. A heat exchanger as claimed in claim 6, in which the gasket includes at least one stiffening strip integral with the parallel walls of the gasket and extending transversely between, and integral with, the longer sides of the frame, the stiffening strip being a symmetrical with respect to an axis bisecting the shorter sides of the frame.

8. A heat exchanger as claimed in claim 3 in which the gaskets are located with several sequences of gaskets that are each in an inverted attitude with respect to a neighbouring sequence.

9. A heat exchanger as claimed in claim 1, in which:

a. the cross sectional area of each perforation of each conductive plate is in the range of 4 to 12.5 X 10 in b. the thickness of each plate is in the range 1.0 to 2.0

X 10 in;

c. the total area of perforations in each plate is in the range 25 to 40 percent of the surface area of the plate;

d. the thickness of each gasket is in the range 0.5 to

1.0 X 10 in;

e. the width of each wall of the gasket is in the range of 1.0 to 1.5 X 10 in; and

f. each gasket and each plate has an aspect ratio in the range 1.5: l to 3.0: 1.

Claims

9. A heat exchanger as claimed in claim 1, in which: a. the cross-sectional area of each perforation of each conductive plate is in the range of 4 to 12.5 X 10 4 in2; b. the thickness of each plate is in the range 1.0 to 2.0 X 10 2 in; c. the total area of perforations in each plate is in the range 25 to 40 percent of the surface area of the plate; d. the thickness of each gasket is in the range 0.5 to 1.0 X 10 2 in; e. the width of each wall of the gasket is in the range of 1.0 to 1.5 X 10 1 in; and f. each gasket and each plate has an aspect ratio in the range 1.5: 1 to 3.0: 1.