GB1558994A - Others heat exchanger - Google Patents

Description

(54) HEAT EXCHANGER (71) We, VLADIMIR GRIGORIE VICH PRONKO, USSR, Moscow, Bolshoi Kozlovsky pereulok 11, kv. 42, EVGENY VALENTINOVICH ONOSOVSKY, USSR, Moscow, ulitsa Zoi i Alexandra Kosmoderaian- skikh, 8/7 kv. 131, ALBERT VLAD1MIRO- VICH CHUVPILO, USSR, Moscow, 3 Mytischinskaya ulitsa 14a, kv. 86, IRINA NIKOLAEVNA ZHURAVLEVA, USSR, Moscow, 4 Parkovaya ulitsa 24, kg. 6.VIK TOR ALEXEEVICH KORNEEV, USSR, Moscow, Nagatinskaya ulitsa 89, kg. 4, DMITRY ALEXEEVICH KLIMENKOV, USSR, Moscow, Chongarsky bulvar, 14, korpus 2, kg. 31, GALINA MIKHAILOVNA SMIRNOVA, USSR, Moscow, ulitsa, Vvedenskogo 11, korpus 1, kv. 7, VLADIMIR VASI LIEVICH USANOV, USSR, Moscow, Novodevichy proezd 2, kg. 5, JURY IVANOVICH IVANOV, USSR, Moscow, Obolensky pereulok 9, korpus 3, kv. 15, BORIS ALEXAN DROVICH CHERNYSHEV, USSR, Moscow, Seleznevskaya ulitsa 40, kg. 10, VASILY DMITRIEVICH NIKITKIN, USSR, Moscow, Tsvetnoi bulvar 25, kv. 95, ANATOLY FEDOROVICH NIKOLAEV, USSR, Leningrad, S hkolnaya ulitsa 5, kv. 42, MAYA STEPANOVNA TRIZNO, USSR, Leningrad, Kirovsky prospekt 16, kv. 32, VALERY GAVRILOVICH KARKOZOV, USSR, Leningrad, Bolshaya Porokhovskaya ultisa 45, kv.

237, TATYANA JULIEVNA VERKHOGLY ADOVA, USSR, Leningrad, prospekt Kosmonavtov 92, kv. 137, EVGENY VLAD IMIROVICH MOSKALEV, USSR, Leningrad, ulitsa Primakova 16, kv. 15, LIDIA IVANOVNA YAKOVLEVA, USSR, Leningradskaya oblast, Vsevolzhsky raion, poselok Kuzmolova, Korotky pereulok 8, all Russian citizens, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to heat exchangers, suitable for use in cryogenic engineering, for example in air separating installations, or in any other branch of engineering which requires highly compact and efficient heat exchangers.

At present, low-temperature refrigerating systems utilize heat-exchangers having a highly-compact surface with good thermal and hydrodynamic properties, and minimum longitudinal heat conduction along the apparatus and non-uniformity of flow distribution over the passage area of the heat exchanger. Such heat exchangers have good technical and economic characteristics. Ideally the design and manufacturing technology of heat exchangers should ensure the highest possible percentage of standardized units and parts and the fullest possible mechanization and automation of their manufacture.

These requirements are satisfied most completely by heat exchangers whose heat-exchanging surfaces are formed by screens assembled into a bank. Such surfaces can be compact and can be made conveniently with the use of simple and cheap appliances.

The use of such screens in heat exchangers can reduce considerably the overall dimensions of the heat exchanger, particularly its length, but may also impair its efficiency due to a considerable transfer of heat over the heat exchanger walls from the hot to the cold end of the exchanger.

A reduction of longitudinal heat conduction and the provision of anisotropic heat conduction, i.e. a maximum heat conduction in the direction of heat transfer between the currents of the fluid media and a low heat conduction along the flow of said media, is attained by the introduction of low-heat-conducting spacers sandwiched between the screens in the bank.

A known heat exchanger construction of the latter form is used for recuperative heat exchangers of helium liquefiers and refrigerators, and consists of spacers provided with holes and screens interconnected rigidly into a bank.

The spacers are made of glue-impregnated paper and have square holes. The screens are woven of wire with square meshes. The screens and spacers are arranged alternately in the so that the holes in the spacers register to form passages for the flow of helium.

The two opposed edges of each hole are parallel to the screen warp while the other two are parallel to the screen weft.

During manufacture of the heat exchanger the assembled bank of screens and spacers is clamped and heated, so that the glue of the spacers softens and penetrates into the meshes between the screen wires, thus interconnecting the spacers with each other and the screen wires, after which the bank is polymerized and solidified. The holes in the spacers form square passages for the flow of helium and the bridges between the spacer holes form pressure tight passage walls in the finished heat exchanger.

The passages for the forward and reverse flows of helium are arranged in a staggered order in the exchanger cross section so that each forward-flow passage is surrounded by four reverse flow passages and each reverseflow passage is surrounded by four forwardflow passages.

The heat exchanger comprises at least one pair of headers communicating with the bank passages. The headers are rigidly connected with the opposite sides of the bank and distribute the forward and reverse flows of helium among the passages of the bank.

Such a heat exchanger is noted for a very valuable property, i.e. anisotropic heat conduction of its structure. A high lateral heat conduction needed for efficient heat transfer is ensured by the use of copper wire screens while a low longitudinal heat conduction reducing considerably the heat transfer along the heat exchanger walls is obtained by the provision of paper spacers sandwiched between the screens.

The square cross section of the passages is most practicable for the woven wire screens since it ensures uniform heat transfer along the cross section of such a heat exchanger because all the wires of the screen serve as ribs of the heat-exchanging surface and take a uniform part in the process of heat transfer.

The woven wire screens can be set either at a certain distance from one another in a bank, or fit tightly against one another as described in French Patent No. 1,500,641.

A disadvantage of such a heat exchanger lies in its structural features caused by the use of woven wire screens.

The screens of this heat exchanger are characterized by an insufficiently intensive heat transfer at a comparatively high hydrodynamic resistance. This should be attributed to an unfavourable profile from the hydrodynamic point of view, said profile being constituted by a system of curved and intertwined cylinders constituted by the individual wires with the fluid flow moving laterally around them.

In order to improve compactness of the heat-exchanging surface in such a heat exchanger it is possible to reduce the diameter of the wires and their spacing in the screen. However, the reduction in diameter is limited by a decreased strength of the wires which hampers the manufacture of woven screens. The requirement of a certain strength of the wire used for making woven screens places also certain restrictions on the selection of the screen material. For example, it is practicable that recuperative heat exchangers of helium liquefiers and refrigerators should comprise screens made of electrolytic copper whose heat conduction grows considerably with the drop of temperature. However, thin wires made of this grade of copper are not strong enough for making woven screens.

Besides, in such a screen heat exchanger with square passages whose cross section is governed by the use of woven wire screens, the relation between the cross sections of the forward and reverse flows is equal to unity which increases the weight and size of the heat exchanger since the pressure of the forward flow of helium is a few times higher than that of the reverse flow.

The design of the header for the staggered square passages of the forward and reverse flows is relatively complicated and difficult from the manufacturing point of view.

Another heat exchanger which comprises alternating spacers and screens rigidly interconnected into a bank is described in German Patent Specification 200,876. The spacers have holes and are made of a low-heat-conducting material. The screens are made of a sheet material having a high thermal conductivity. Each screen is provided with mesh portions formed by screen elements, i.e. by bridges arranged in the plane of the screen.

The screens and spacers are assembled into a bank in an alternating order so that the corresponding holes in all the spacers coincide, forming passages for the fluid media. The heat exchanger comprises headers connected rigidly to the bank and distributing the fluid media among the passages of the heat exchanger.

This heat exchanger is devoid of some of the disadvantages of the above described known heat exchanger since it has plate-type screens instead of the woven wire screens.

In this case the selection of the screen material and the size of the elements forming the screen meshes is not limited by the strength considerations.

Besides, the screen of a sheet material ensures uniform heat transfer along the cross section of the heat exchanger with slotted passages wherein the relationship between the forward and reverse flows of the fluid medium can vary within wide limits depending on pressure and rates of flow.

However, the use of screens made of a sheet material instead of woven wire limits compactness because the screens in the heat exchanger can be set only at a certain distance from one another, which distance is equal to the thickness of the spacer.

Besides, the profile of the screen mesh elements in such a heat exchanger is disadvantageous from the hydrodynamic point of view, said profile consisting of a system of parallel plates around which the fluid medium flows. This results in a high hydrodynamic resistance at an insufficiently high intensity of heat transfer in the exchanger under consideration.

In accordance with the present invention there is provided a heat exchanger comprising a plurality of spacers having holes, a plurality of screens made of sheet metallic material having a thermal conductivity greater than that of the material of the spacers, the screens and spacers being arranged alternately and rigidly interconnected in a bank, the holes in the spacers registering to form fluid passages for flow of fluid media through the bank, each of the screens including within each fluid passage a multiplicity of meshes defined and separated by screen portions lying at an angle to the plane of the screen, and at least one pair of headers communicating with the passages and connected rigidly to the opposite ends of the bank.

Such heat exchanger can ensure a very favourable profile of the screen portions from the hydrodynamic point of view, said profile being constituted by a system of short parallel plates washed longitudinally or at a small angle by the flow of fluid medium. This brings about a more favourable relationship between the intensity of heat transfer and the hydrodynamic resistance.

Such screens made of a sheet material can guarantee compactness and owing to the inclination of the mesh-fornaing portions, the screens in the bank can fit tightly against one another or even enter one another partly, which likewise can lead to greater compactness.

It is preferable that the parts of each screen located between the passages and around its periphery be imperforate to increase the intensity of heat transfer due to a reduction in the thermal resistance of the heat exchanger walls.

It is also preferred that said parts of each screen located between the passages and around its periphery should be provided with projections for positioning the screens in the bank during assembly.

This ensures simple and reliable fixing of the screens in the bank thus reducing the danger of such a secondary effect as nonuniform distribution of fluid media among the passages of the heat exchanger.

The screens of heat exchangers to be used as recuperative heat exchangers can be made of various materials, e.g. electrolytic sheet copper or pure aluminium whose heat conduction grows with the drop of temperature.

In the regenerators of gas-fired refrigerating machines the screens can be made of sheet lead which retains a considerably high heat capacity at cryogenic temperatures.

A more complete understanding of the invention will be had from the following detailed description, given by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic longitudinal section through first heat exchanger shown with the headers omitted for convenience; Fig. 2 is plan view of the heat exchanger shown in Figure 1; Fig. 3 is a schematic longitudinal section through a second heat exchanger also shown with the headers omitted for convenience; Fig. 4 is plan view of the heat exchanger of Figure 3; Fig. 5 is a schematic longitudinal section through another heat exchanger embodying the invention; Fig. 6 is a section taken along the line VI-VI in Fig. 5; Fig. 7 is a detail plan view of a screen mesh; Fig. 8 is a view taken in the direction of arrow A in Fig. 7;; Fig. 9 is a section taken along line IX-IX in Fig. 8; Fig. 10 is a detail plan view of another screen mesh; Fig. 11 is a view taken in the direction of arrow B in Fig. 10; Fig. 12 is a section taken along line XII XII in Fig. 11; Fig. 13 is an enlarged view of the fragment I in Fig. 2 the spacers being omitted for convenience; Fig. 14 is an enlarged view of the fragment II in Fig. 4, the spacers being omitted for convenience; Fig. 15 is a schematic plan view of a screen; Fig. 16 is a schematic plan view of a screen having portions of solid sheet material; Fig. 17 is a schematic plan view of a screen having portions of solid sheet material with locating projections; Fig. 18 is a section taken along line XVIII- XVIII in Fig. 17, on an enlarged scale with the inclination of the elements not being shown for convenience.

Fig. 19 is a fragmentary schematic view showing screens with projections jointed together with spacers.

The screen heat exchanger shown in Figures 1 and 2 comprises alternating spacers 2 and screens 3 rigidly interconnected into a bank 1. The spacers 2 have holes which form passages 4 in the bank 1 for the flow of the fluid medium, for example helium. The passages 4 may vary in cross section and as shown are, of rectangular configuration. The passages c for the forward flow c are of different width to those d for the reverse flow D. The rectangular or slotted cross section of the passages makes it possible to select within wide limits (from 1 to 5 and over) the relationship between the cross sectional areas of the forward and reverse flow passages 4 depending on their pressure and flow rates. In its turn, this makes it possible to produce a screen heat exchanger which, for given operating conditions, has an optimum weight, size and hydrodynamic resistance.

The passages may also be of a square cross section as shown in Fig. 3 and 4. In this case the ratio of the total cross sectional areas of the passages for the forward flow C to that of those for the reverse flow along arrow D is equal to unity. Square passages are practicable when the volumetric flow rates of the forward and reverse flows are nearly the same.

In some cases the passages may be of a circular or round cross section as shown in Figs. 5 and 6.

The spacers 2 may each comprise a film of epoxy resin having a good adhesion to majority of metals. This film is made by extrusion at a high speed; approaching 60 m/hr. The material of the spacers is cheap and displays high strength at cryogenic temperatures.

In other cases the material of the spacers 2 as well as that of the screens 3 is selected to suit the operating conditions of the exchanger.

For example, when the heat exchanger operates under the conditions where longitudinal heat conduction is unimportant the spacers may be made from sheet solder or from a material with a solder applied thereon.

The screens 3 are made from a sheet metal material whose heat conduction is consider ably higher than that of the material of the spacers 2 which ensures anisotropic heat conduction of the screen heat exchanger, i.e.

a maximum possible lateral heat conduction which intensifies heat transfer, and a low longitudinal heat conduction which reduces the transfer of heat from the hot to the cold end of the heat exchanger along its walls.

Each screen 3 is made so that its portions or elements 5 (Figs. 7, 8, 10, 11) forming the meshes 6 lie at an angle a (Figs. 9 and 12) to the plane of the screen 3.

It is practicable that the angle a should be from 45 to 90 . Inclination of the elements 5 of the meshes 6 is produced when the screen is machine made from a sheet material on and is determined on the one hand by the plasticity of the material and, on the other, by the optimum relationship for each particular application of the heat exchanger, between its thermal and hydrodynamic properties.

The individual meshes 6 are polygonal in shape, as determined by the shape of the cutting tool of the machine used for making the screen.

The screens can be made from a coiled sheet of metal 0.054.5 mm thick loaded into the machine. A screen whose surface arc is 200(W20000 m2 per cubic meter of space occupied by the screen is characterized by a sufficiently high accuracy of the basic dimensions, reaching 3-5 %.

The screen can be made of any, adequately plastic sheet material.

With respect to cryogenic engineering, the most promising tendency is the employment of electrolytic sheet copper for the recuperative heat exchangers of helium liquefiers and refrigerators and of sheet lead for the regenerators of gas-fired refrigerating machines.

The relative location of the screens in the bank 1 may vary as shown in Figs. 13 and 14 and depends on the shape of the passages 4. (Figures 13 and 14 each show two superposed screens, one drawn in thick lines and the other in thin line). For instance, the best relative arrangement of the meshes for the rectangular or slotted passages 4 (Figs. 1 and 2) is shown in Fig. 13, in which case the total length of the mesh elements in the cross section of the passage is minimum and, as a consequence, the heat transfer and the strength of the side walls of the passages are greatest.

The most practicable relative arrangement of the screens 3 for the square passages 4 (Figs. 3, 4) is shown in Fig. 14. This arrangement of the screens ensures uniform heat transfer and strength of all the four walls of the square passage 4. The two screens are shown turned through an angle,lJ=90" with respect to each other.

In the passages 4 of a circular and round cross section shown in Fig. 6 the screens 3 can be arranged in any arbitrary way relative to one another.

Besides, the screens 3 can be arranged differently in the bank; they may be spaced apart at a certain distance from one another, fit tightly to each other, or else enter partly into one another.

The screens of a heat exchanger may also differ in construction.

The one-piece screen 3 shown in Fig. 15 is easiest to manufacture. However, the passages 4 in a heat exchanger having such screens may differ somewhat in cross section which leads to irregular distribution of the fluid flow among the passages 4 and, in some cases, to a reduction in the thermal characteristics of the heat exchanger. This is explained by the fact that the spacers 2 have a certain tolerance on thickness so that the surplus material of the spacers 2 is squeezed into the passages 4 when the heat exchanger is baked.

The screen 3 with the portions 7 (Fig. 16) of solid sheet material located between the passages 4 and along the periphery ensures identical cross sections of the passages 4. The bridges 8 (Fig. 2) of the spacers 2 in this case are narrower than the solid portions 7 of the screen 3 by the value which depends on the tolerance on the width of the spacer 2.

The surplus material of the spacer 2 squeezed out during baking is always located between the solid portions 7 of the adjacent screens 3 and does not distort the cross section of the passages 4.

During the manufacture of the heat exchanger, the screens 3 in the banks shown in Fig. 15 and 16 are fixed by external retainers (not shown in the drawing).

The screen 3 may have fixing projections 9 (Fig. 17) on the solid portions 7 between the passages 4 and along its periphery which makes it possible to locate the screens 3 during manufacture accurately with relation to one another both in cross section and along the height of the bank 1 as shown in Fig. 19.

Besides, the use of the screens shown in Figs. 16 and 17 in the screen heat exchanger gives a reduction in the thermal resistance of its walls and intensifies heat transfer in the apparatus.

The headers 10 and 11 (Fig. 5) intended to distribute the forward and reverse flows of helium among the passages 4 of the screen heat exchanger are rigidly connected to the bank 1.

The parts and units of the screen heat exchanger, i.e. spacers 2 and screens 3 and the headers 10, 11 are flat and can easily be standardized.

Thus, it is possible to provide an efficient and highly-compact screen heat exchangers with anisotropic heat conduction of its structare, consisting of standardized units and parts whose manufacture can easily be mechanized and automated.

The operation of screen heat exchanger embodying to the present invention used as a recuperative heat exchanger in cryogenic helium installations is as follows.

The fluid medium, in this case warm gaseous helium of a forward flow whose direction is shown by arrows C moves from the compressor (not shown in the drawing) into the header 10 wherein it is distributed uniformly among the passages 4 of the bank 1 marked with letter c in Figs. 1 to 6. Moving through these passages, helium flows around the screens 3 and transfer heat to them. Then the heat received by the screens 3 is transferred due to their heat conduction into the passages marked d.

Then the helium cooled enters the header 11 wherefrom part of the helium flows into a gas expansion machine (not shown) expands there and is additionally cooled down. The other part of the forward flow of helium is throttled down in valves (not shown) and returns into the header 11 in the form of a cold reverse flow combined with the flow of helium leaving the gas expansion machine; in the header 11 this helium is distributed among the passages 4 marked with letter d. The reverse flow of helium moves through these passages in the direction shown by arrow D and, flowing around the screens 3, is heated, accumulates in the header 10 and leaves the heat exchanger.

An experimental specimen of the screen heat exchanger has undergone laboratory tests which have shown that the screen heat exchanger according to the invention is characterized by a good relationship between heat transfer and hydrodynamic resistance along with comparatively small size and weight.

Compactness of the heat-exchanging surface formed by the screens of various dimensions ranges from 2000 to 20000 m2 of surface per cubic meter of free volume occupied by the screens.

The screen heat exchanger according to the present invention is technologically processable, its parts can be highly standardized and the basic processes of its manufacture yield themselves readily to mechanization and automation.

WHAT WE CLAIM IS: 1. A heat exchanger comprising a plurality of spacers having holes, a plurality of screens made of sheet metallic material having a thermal conductivity greater than that of the material of the spacers, the screens and spacers being arranged alternately and rigidly interconnected in a bank, the holes in the spacers registering to form fluid passages for flow of fluid media through the bank, each of the screens including within each fluid passage a multiplicity of meshes defined and separated by screen portions lying at an angle to the plane of the screen, and at least one pair of headers communicating with the passages and connected rigidly to the opposite ends of the bank.

2. A heat exchanger according to claim 1 wherein for each screen the angle of the screen portions to the plane of the screen is from 45 to 90 .

3. A heat exchanger according to claim 1 or 2 wherein parts of each screen located between the passages and around its periphery are imperforate.

4. A heat exchanger according to claim 3 wherein the imperforate screen parts are provided with protrusions for positioning the screens in the bank.

5. A heat exchanger substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. the solid portions 7 of the adjacent screens 3 and does not distort the cross section of the passages 4. During the manufacture of the heat exchanger, the screens 3 in the banks shown in Fig. 15 and 16 are fixed by external retainers (not shown in the drawing). The screen 3 may have fixing projections 9 (Fig. 17) on the solid portions 7 between the passages 4 and along its periphery which makes it possible to locate the screens 3 during manufacture accurately with relation to one another both in cross section and along the height of the bank 1 as shown in Fig. 19. Besides, the use of the screens shown in Figs. 16 and 17 in the screen heat exchanger gives a reduction in the thermal resistance of its walls and intensifies heat transfer in the apparatus. The headers 10 and 11 (Fig. 5) intended to distribute the forward and reverse flows of helium among the passages 4 of the screen heat exchanger are rigidly connected to the bank 1. The parts and units of the screen heat exchanger, i.e. spacers 2 and screens 3 and the headers 10, 11 are flat and can easily be standardized. Thus, it is possible to provide an efficient and highly-compact screen heat exchangers with anisotropic heat conduction of its structare, consisting of standardized units and parts whose manufacture can easily be mechanized and automated. The operation of screen heat exchanger embodying to the present invention used as a recuperative heat exchanger in cryogenic helium installations is as follows. The fluid medium, in this case warm gaseous helium of a forward flow whose direction is shown by arrows C moves from the compressor (not shown in the drawing) into the header 10 wherein it is distributed uniformly among the passages 4 of the bank 1 marked with letter c in Figs. 1 to 6. Moving through these passages, helium flows around the screens 3 and transfer heat to them. Then the heat received by the screens 3 is transferred due to their heat conduction into the passages marked d. Then the helium cooled enters the header 11 wherefrom part of the helium flows into a gas expansion machine (not shown) expands there and is additionally cooled down. The other part of the forward flow of helium is throttled down in valves (not shown) and returns into the header 11 in the form of a cold reverse flow combined with the flow of helium leaving the gas expansion machine; in the header 11 this helium is distributed among the passages 4 marked with letter d. The reverse flow of helium moves through these passages in the direction shown by arrow D and, flowing around the screens 3, is heated, accumulates in the header 10 and leaves the heat exchanger. An experimental specimen of the screen heat exchanger has undergone laboratory tests which have shown that the screen heat exchanger according to the invention is characterized by a good relationship between heat transfer and hydrodynamic resistance along with comparatively small size and weight. Compactness of the heat-exchanging surface formed by the screens of various dimensions ranges from 2000 to 20000 m2 of surface per cubic meter of free volume occupied by the screens. The screen heat exchanger according to the present invention is technologically processable, its parts can be highly standardized and the basic processes of its manufacture yield themselves readily to mechanization and automation. WHAT WE CLAIM IS:

1. A heat exchanger comprising a plurality of spacers having holes, a plurality of screens made of sheet metallic material having a thermal conductivity greater than that of the material of the spacers, the screens and spacers being arranged alternately and rigidly interconnected in a bank, the holes in the spacers registering to form fluid passages for flow of fluid media through the bank, each of the screens including within each fluid passage a multiplicity of meshes defined and separated by screen portions lying at an angle to the plane of the screen, and at least one pair of headers communicating with the passages and connected rigidly to the opposite ends of the bank.

2. A heat exchanger according to claim 1 wherein for each screen the angle of the screen portions to the plane of the screen is from 45 to 90 .

3. A heat exchanger according to claim 1 or 2 wherein parts of each screen located between the passages and around its periphery are imperforate.

4. A heat exchanger according to claim 3 wherein the imperforate screen parts are provided with protrusions for positioning the screens in the bank.

5. A heat exchanger substantially as herein described with reference to the accompanying drawings.