PLATE HEAT EXCHANGER

Abstract: In a series of heat exchange plates (5, 6), each being rectangular with ports (7, 8, 9, 10) in its corner portions, alternate plates (6) are fully sealed and coact with intermediate plates (5) to define two groups of elongated passages through which the respective heat exchanger fluids (A, B) flow. Each intermediate plate (5) is only partially sealed and defines with one (6) of the two adjacent fully-sealed plates an open space (20) communicating directly with atmosphere, the partial sealing consisting of port sealing means (7a, 8a, 9a, 10a) interconnecting respective pairs of opposing ports to form channels through which the two fluids (A, B) flow without entering said open space (20). The open spaces (20) form paths through which any leakage of either fluid (A, B) can escape to atmosphere, thus preventing contamination of either fluid by the other.

Description: Plate heat exchanger This invention relates to plate heat exchangers of the type having a series of heat exchanger plates sealed from each other and forming interplate passages for flow of r two fluids which exchange heat through the plates. More particularly, the invention relates to a novel arrangement of the plates and the sealing means which allows any leakage of either fluid to escape to atmosphere without contaminating the other fluid. Background of the Invention The heating and cooling of "potable" or drinking water is accomplished on a continuous basis in residential and commercial structures using basically two types of devices. The first, the most common, is the self-contained heater or cooler that adds or extracts energy utilizing conventional utility sources such as gas, electricity and oil. This type of unit is found in many commercial installations, and in residential applications it is used almost exclusively. The second type of device used for this purpose is the fluid to fluid heat exchanger. The heat exchanger typically uses steam or hot water from the central boiler system, used to heat the buil- ding, to heat hot water for public consumption. In the case of cooling, the heat exchanger would draw cold water from the cent¬ ral chiller circuit, used to cool the building, to cool the pot¬ able water. This type of device typically requires too large a capital investment to be cost-effective in a residential situa- tion. It is used almost exclusively in commercial applications. Most "model" building mechanical codes require that the heat exchangers used for potable water service be of either the "double-wall" construction type or have adequate monitoring devices to prevent cross contamination from the non-potable fluid to the potable fluid. Some codes will allow only the double-wall construction, considering the monitoring devices not fail-safe enough to protect public health. The state of the art in double-wall heat exchangers is a shell and tube design that is of such low efficiency as to make it almost impractical. The use of this type of device is rather limited and lends itself mostly to low volume applications. Another field of use of a heat exchanger of a "double-wall" construction type is in electrical transformers where the windings require liquid cooling. In this connection transformer oil is the coolant in the transformer and the oil is cooled either by air or water in a heat exchanger. In the case of water-cooled transformer oil, there is a request to avoid conta¬ mination of the oil with water. The reason why is that the transformer windings insulation can get damaged by water and "hot pockets" can occur, the consequences being risks of short circuits, explosion or insufficient cooling. Object of The Invention The principal object of the present invention is to provide a heat exchanger of the sealed plate type which allows leakage of either of the two heat exchanging fluids to escape to atmosphere so as to avoid contaminating the other fluid. Brief Summary of The Invention In a plate heat exchanger made according to the invention, each plate of a series is generally rectangular and has ports in corner portions thereof, each plate also having a front face anda rear face, said ' series including alternate plates and plates intermediate said alternate plates. Located on the front face of each alternate plate is first sealing means including boundary gasket means engaging the rear face of an adjacent intermediate plate to define an elongated passage for flow of a heat exchanging fluid from a said port at one end to a said port at the opposite end of the flow passage. Alternate ones of these passages accommodate flow of a first said fluid while the other passages accommodate flow of a second said fluid. The first sealing means also include port gasket means engaging said rear face outside said flow passage and interconnecting opposing ports to form channel means for flow of one of said fluids by- passing said flow passage. An open space communicating directly with atmosphere is formed between the front face of each inter¬ mediate plate and the opposing rear face of an adjacent alter¬ nate plate. Second sealing means is located in this space and include port sealing means interconnecting pairs of opposing ports to form bypass channels through which the two fluids flow without entering the open space. Any leakage of either fluid can escape to atmosphere by way of an open space, thereby preventing contamination of either fluid by the other. Preferably, each plate has a herringbone pattern of corrugations to stiffen the plate and alternate ones of said alternate plates are turned 180° in their own planes relative to the other alternate plates, while alternate ones of said intermediate plates are turned 180° in their own planes relative to the other intermediate plates, each alternate plate being in phase with one of the two adjacent intermediate plates but being turned 180° in its own plane relative to the other adjacent intermediate plate. Brief Description of The Drawings For a better understanding of the invention, reference may be had to the accompanying drawings in which Fig. 1 is an exploded schematic view of a series of heat exchange plates and their ' gaskets, in one arrangement according to the invention; and Fig. 2 is a cross-sectional view of part of an assembly of eight sealed plates according to Fig. 1. Detailed Description Referring to Fig. 1, the series of heat exchanger plates shown there consists of alternate plates 6 and other plates 5 inter¬ mediate the alternate plates. Each plate is generally rectangu- lar and has through-flow ports 7, 8, 9 and 10 in its four corner portions. Each plate also has a front face 11 and a rear face (not shown). On the front face 11 of each alternate plate 6 is first sealing means comprising a boundary gasket 13 enclosing an area which includes two ports 7-8 and a heat transfer surface formed by a herringbone pattern of corrugations 14. The first sealing means also comprises two port gaskets 15 and 16 surrounding the other two ports 9 and 10, respectively. The first sealing means is preferably made of rubber or plastics material. On the front face of each intermediate plate 5 is second sealing means comprising four port gaskets 7a, 8a, 9a and 10a surroun¬ ding ports 7, 8, 9 and 10, respectively. In this embodiment the second sealing means consists of rings made of rubber or plas¬ tics material. However, the second sealing means can instead be a weld joint or a soldered joint connecting the front face of the intermediate plate 5 and the opposing rear face of the alternate plate 6 with each other at the four ports. In this connection the weld joint or the soldered joint surrounds the ports 7, 8, 9 and 10, respectively. As will be readily understood by those skilled in the art, the various gaskets 7a-10a, 13 and 15-16 are held in narrow grooves pressed in the respective plates, grooves for boundary gaskets 13 being shown at 13a in Fig. 2. Also, the illustrated plates constitute only part of a complete series forming a pack of plates mounted on horizontal carrying bars and compressed bet¬ ween vertical frame members (not shown), one or both of these members having fittings through which the two heat exchanging fluids are passed separately to and from the plate pack. This arrangement, being conventional, is not described further. In the illustrated embodiment of the invention, each plate 5 is identical with adjacent plate 6 being in front of that; plate 5. However, the alternate plates 6 could be different from each other so that certain of them have corrugations giving a high flow resistance while others have corrugations giving a low flow resistance. Each alternate plate 6 is turned 180° in its own plane relative to the next alternate plate 6. Thus, of the three alternate plates 6 in Fig. 1, the middle one has its corruga¬ tions 14 slanting downward from the points or centers of the herringbones, while the other two have their corrugations 14 slanting upward from the centers of the herringbones. Similarly, each intermediate plate 5 is turned 180° in its own plane relative to the next intermediate plate 5. Thus, of the three intermediate plates 5 in Fig. 1, the middle one has its corruga¬ tions 14 slanting upward from the centers of the herringbones, while the opposite is true of the other two. With the gasketed plates pressed together in a pack, the first gasket means 13, 15-16 on the front face of each alternate plate 6 engages the rear face of an adjacent intermediate plate 5, thereby defining an elongated passage 18 for flow of a heat exchanging fluid from a port 7 at one end of the passage to a port 8 at the opposite end of the passage (Fig. 1). The gaske- ting is such that alternate ones of these flow passages 18 accommodate flow of a first heat exchanging fluid while the other passages accommodate flow of a second heat exchanging fluid. Thus, in Figs. 1 and 2 one of the fluids flows through the middle passage 18 while the other fluid flows through the other two passages 18. Port gaskets 15 and 16 of each first gasket means engage the opposing rear face of an adjacent intermediate plate 5 outside the corresponding passage 18, so as to interconnect opposing ports 9-9 and 10-10. Gaskets 15-16 thus form respective channels for flow of one of the two fluids bypassing the corresponding passage 18. The front face of each intermediate plate 5 and the opposing rear face of the next alternate plate 6 form an intervening open space 20 which communicates directly with atmosphere, since there is no boundary gasket 13 between these two plate faces. Each open space 20 contains port gaskets 7a-10a of the second gasket means (Fig. 1). This second gasket means or the weld joint or the soldered joint thus forms respective bypass chan¬ nels connecting the four ports of each intermediate plate 5 with the opposing four ports of the alternate plate 6 immediately in front of the plate 5. These four channels provide paths for flow of the two heat exchanging fluids without entering the corre¬ sponding open space 20. In operation, the two heat exchanging fluids are introduced to the plates from the left in Fig. 1, as shown at A and B, the paths of the two fluids being shown in broken lines. Fluid A flows in a path Al through ports In the upper left hand corners of the plates while branches of this fluid flow downward through the first and third passages 18 to join the returning fluid in a path A2 through ports in the lower left hand corners of the plates. The other fluid B flows in a path Bl through ports in the lower right hand corners of the plates while a branch of this fluid flows upward through the second passage 18 to join the returning fluid in a path B2 through ports in the upper right hand corners of the plates. As shown in Fig. 1, the return paths A2 and B2 exit through fittings in a header (not shown) which also has fittings for supplying the two fluids. However, in some instances the heat exchanger may have headers at opposite ends, each with two fittings for the respective fluids, so that the fluids do not return to the same header which supplied them. In that case, of course, each plate may have only two throughflow ports. Also, although the plates as shown are gasketed for parallel flow of each fluid, they may be arranged for series flow. The thickness of the second sealing means 7a-10a is considerably less than that of the first sealing means 13, 15-16. Conse¬ quently, the open spaces 20 are considerably thinner than the fluid passages 18, as shown in Fig. 2. In fact, especially when using weld joints or soldered joints as sealing means, the dis¬ tance between the front face of the intermediate plate and the opposing rear face of the alternate plate will be exceedingly small. The open spaces 20 make cross contamination of the two fluids A and B virtually impossible. As shown in Fig. 1, each flow passage 18 is formed by plates 5 and 6 which are 180° out of phase with each other, so that the corrugations 14 of one plate cross and abut the corrugations of the other plate. Thus, the two plates contact each other. On the other hand, each open space 20 is formed by plates 5 and 6 which are identical and in phase with each other, so that the ridges of the corrugations 14 of the front face of the plate 5 will fall down into corresponding valleys of the corrugations 14 of the opposing rear face of the adjacent plate 6 (see Fig. 2), thereby reducing the distance, i.e. the gap between the front face of the plate 5 and the opposing rear face of the adjacent plate 6. Moreover, the plates 5 and 6 at least at certain places will come into metallic contact with each other, whereby the heat transfer coefficients will be improved. In certain situa- tions, however, it is preferable to insert a heat conducting material in these open spaces 20. An example of such material is a metal mesh, the voids in the mesh forming escape paths for • any leakage. Another such material is a heat conducting grease, which may be coated on the opposing plate surfaces forming the spaces 20. An example of such a grease is Dow Coming's "340 Heat Sink Compound", which is a silicone material heavily filled with heat conductive metal oxides. If a leak occurs, the grease will be expelled from a space 20 due to the differential between the pressure in flow channels 18 and atmospheric pressure. The first sealing means in this specification has been described as a gasket means preferably made of rubber or plastics material. However, the first sealing means like the second sealing means could be a weld joint or a soldered joint.

Claims: Claims 1. Plate heat exchanger comprising a series of heat exchanger plates arranged in a pack, each plate being generally rectangu- lar and having through-flow ports in corner portions thereof, said series including alternate plates and other plates inter¬ mediate the alternate plates, first sealing means between each alternate plate and one of the two adjacent intermediate plates, said first sealing means defining an elongated passage for flow of a heat exchanging fluid from a said port at one end to a said port at the opposite end of said flow passage, alter¬ nate ones of said passages accommodating flow of a first said fluid and the other passages accommodating flow of a second said fluid, said first sealing means also defining a channel inter- connecting opposing ports to accommodate flow of one of said fluids bypassing said flow passage, each alternate plate and the other of said two adjacent intermediate plates forming between them a gap communicating with atmosphere, and second sealing means in each said gap to define channels interconnecting oppo- sing ports and through which both of said fluids can pass sepa¬ rately without entering said gap, said gaps forming paths through which leakage of a said fluid can escape to atmosphere. 2. Plate heat exchanger according to claim 1, in which said second sealing means has such a design that said gaps are thinner than said flow passages. 3. Plate heat exchanger according to claim 1 or 2, in which said second sealing means constitutes the only sealing means in said gap. 4. Plate heat exchanger according to anyone of claims 1-3, in which said second sealing means is a gasket means made of rubber forming respective bypass channels connecting the four ports of each intermediate plate 5 with the opposing four ports of the alternate plate 6 immediately in front of the plate 5. 5. Plate heat exchanger according to anyone of claims 1-3, in which said second sealing means is a weld joint forming respective bypass channels connecting the four ports of each intermediate plate 5 with the opposing four ports of the alternate plate 6 immediately in front of the plate 5. 6. Plate heat exchanger according to anyone of claims 1-3, in which said second sealing means is a soldered joint forming respective bypass channels connecting the four ports of each intermediate plate 5 with the opposing four ports of the alter¬ nate plate 6 immediately in front of the plate 5. 7. Plate heat exchanger according to anyone of the preceding claims, in which each of said plates is corrugated. 8. Plate heat exchanger according to claim 7, in which the corrugations of each plate form a herringbone pattern. 9. Plate heat exchanger according to anyone of the preceding claims, in which alternate ones of said alternate plates are turned 180° in their own planes relative to the others of said alternate plates, alternate ones of said intermediate plates being turned 180° relative to the others of said intermediate plates. 10. Plate heat exchanger according to claim 9, in which each of said alternate plates is in phase with one of the two adjacent intermediate plates and is turned 180° in its own plane rela¬ tive to the other of said two adjacent intermediate plates. 11. Plate heat exchanger comprising a series of heat exchanger plates arranged in a pack with a space between each pair of adjacent plates, each plate being generally rectangular and having a through-flow port in each of its four corner portions, each plate also having a front face and a rear face, said series including alternate plates and plates intermediate the alternate plates, first sealing means located on the front face of each alternate plate and including boundary sealing means engaging the opposing rear face of an adjacent intermediate plate to define an elongated passage for flow of a heat exchanging fluid from a said port at one end to a said port at the opposite end of said flow passage, alternate ones of said passages accommo¬ dating flow of a first said fluid and the other passages accom¬ modating flow of a second said fluid, said first sealing means also including two port sealing means engaging said rear face outside said flow passage and each interconnecting a pair of opposing ports to form a channel for flow of one of said fluids bypassing said flow passage, and second sealing means located on the front face of each intermediate plate and including four port sealing means engaging the opposing rear face of an adja¬ cent alternate plate, said four port sealing means interconnec¬ ting respective pairs of opposing ports to form four bypass channels for through-flow of said two fluids, said front face of each intermediate plate and the opposing rear face of an adja- cent alternate plate defining between them an open space commu¬ nicating directly with atmosphere, said open spaces forming paths through which leakage of a said fluid can escape to atmosphere.

Inventors: DAHLGREN ARTHUR, KAELLROT MAGNUS, STROEMBLAD MATS, DAHLGREN, ARTHUR, KAELLROT, MAGNUS, STROEMBLAD, MATS
Applicants: ALFA LAVAL THERMAL, ALFA-LAVAL THERMAL AB
Application year: 1985
Main classification: F28F3
IPC codes: F28D9, F28F3