A REFRIGERATION SYSTEM AND METHOD

Abstract

A refrigeration system includes a compressor for compressing a gaseous refrigerant, such that the temperature and pressure thereof increases, whereas the boiling point thereof decreases; a condenser, in which the gaseous refrigerant from the compressor exchanges heat with a high temperature heat carrier, said heat exchange resulting in the refrigerant condensing; an expansion valve reducing the pressure of liquid refrigerant from the condenser, hence reducing the boiling point of the refrigerant; an evaporator, in which the low boiling point refrigerant exchanges heat with a low temperature heat carrier, such that the refrigerant vaporizes; and a suction gas heat exchanger exchanging heat between high temperature liquid refrigerant from the condenser and low temperature gaseous refrigerant from the evaporator. The low temperature gaseous refrigerant entering the suction gas heat exchanger contains a certain amount of low temperature liquid refrigerant, said low temperature liquid refrigerant vaporizing as a result of the heat exchange with the high temperature liquid refrigerant from the condenser. Disclosed is also a refrigeration method.

Claims

1. A refrigeration system comprising: a compressor for compressing a gaseous refrigerant, such that the temperature and pressure thereof increases, wherein the boiling point thereof increases; a condenser, in which the gaseous refrigerant from the compressor exchanges heat with a high temperature heat carrier, said heat exchange resulting in the refrigerant condensing; an expansion valve reducing the pressure of liquid refrigerant from the condenser, hence reducing the boiling point of the refrigerant; an evaporator, in which the low boiling point refrigerant exchanges heat with a low temperature heat carrier, such that the refrigerant vaporizes; and a suction gas heat exchanger exchanging heat between high temperature liquid refrigerant from the condenser and low temperature gaseous refrigerant from the evaporator, wherein the low temperature gaseous refrigerant entering the suction gas heat exchanger contains a certain amount of 2-15 percent by mass of low temperature liquid refrigerant, said low temperature liquid refrigerant vaporizing as a result of the heat exchange with the high temperature liquid refrigerant from the condenser.

2. The refrigeration system according to claim 1, wherein the certain amount of low temperature liquid refrigerant amounts to 5-10 percent by mass.

3. The refrigeration system according to claim 2, wherein the certain amount of low temperature liquid refrigerant amounts to 6-9 percent by mass.

4. The refrigeration system according to claim 3, wherein the certain amount of low temperature liquid refrigerant amounts to 7 percent by mass.

5. The refrigeration system according to claim 1, wherein the evaporator is a plate heat exchanger comprising heat exchanger plates with at least first, second, third and fourth large port openings and a dividing surface dividing the heat exchanger plates into a first heat exchanging portion and a second heat exchanging portion, wherein the second heat exchanging portions are provided with first and second small port openings to form an integrated suction gas heat exchanger.

6. The refrigeration system according to claim 5, wherein the dividing surface divides the heat exchanger plates into the first heat exchanging portion and the second heat exchanging portion, so that fluid passing between the first and second large port openings exchanges heat with fluids passing between the third and fourth port openings over the first heat exchanging portion of each plate and fluid passing between the first and second small port openings over the second heat exchanging portion of each plate.

7. The refrigeration system according to claim 5, wherein the dividing surface is arranged between neighbouring sides of the heat exchanger plates.

8. The refrigeration system according to claim 5, wherein the dividing surface comprises a flat surface provided at the same height as areas surrounding the first and second large port openings.

9. The refrigeration system according to claim 5, wherein the dividing surface extends between the first large port opening and the remaining large port openings, and wherein the first and second small port openings are arranged on the same side of the dividing wall as the first large port opening.

10. A refrigeration method comprising the steps of in a compressor, compressing a gaseous refrigerant, such that the temperature and pressure thereof increases, wherein the boiling point thereof increases; feeding the gaseous refrigerant to a condenser, in which the gaseous refrigerant from the compressor exchanges heat with a high temperature heat carrier, said heat exchange resulting in the refrigerant condensing; by an expansion valve, reducing the pressure of liquid refrigerant from the condenser, hence reducing the boiling point of the refrigerant; feeding the low boiling point refrigerant to an evaporator, in which the low boiling point refrigerant exchanges heat with a low temperature heat carrier, such that the refrigerant partially vaporizes; and in a suction gas heat exchanger integrated with the evaporator, exchanging heat between high temperature liquid refrigerant from the condenser and low temperature gaseous refrigerant from the evaporator, wherein the low temperature gaseous refrigerant entering the suction gas heat exchanger contains a certain amount of 2-15 percent by mass of low temperature liquid refrigerant, said low temperature liquid refrigerant vaporizing as a result of the heat exchange with the high temperature liquid refrigerant from the condenser.

11. The refrigeration method according to claim 10, wherein the certain amount of low temperature liquid refrigerant amounts to 5-10 percent by mass.

12. The refrigeration method according to claim 11, wherein the certain amount of low temperature liquid refrigerant amounts to 6-9 percent by mass.

13. The refrigeration method according to claim 12, wherein the certain amount of low temperature liquid refrigerant amounts to 7 percent by mass.

14. The refrigeration method according to claim 10, comprising the step of exchanging heat between the refrigerant and the low temperature heat carrier in the evaporator in a co-current flow.

15. The refrigeration method according to claim 10, comprising the step of reversing the flow of refrigerant by a four-way valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In the following, the invention will be described with reference to appended drawings, wherein:

[0040] FIG. 1 is an exploded perspective view of a heat exchanger according to one embodiment of the present invention,

[0041] FIG. 2 is an exploded perspective view of a part of the heat exchanger of FIG. 1, illustrating a first heat exchanger plate and a second heat exchanger plate of the heat exchanger,

[0042] FIG. 3 is a schematic section view of another part of the first heat exchanger plate according to one embodiment, illustrating identical depth of grooves of the first heat exchanger plate,

[0043] FIG. 4 is a schematic section view of a part of the second heat exchanger plate according to one embodiment, illustrating an alternating depth of grooves of the second heat exchanger plate,

[0044] FIG. 5 is a schematic section view of a part of a heat exchanger comprising first and second heat exchanger plates according to one embodiment, wherein the first and second heat exchanger plates are alternatingly arranged,

[0045] FIG. 6a is a schematic front view of the first heat exchanger plate according to one embodiment, illustrating a corrugated herringbone pattern thereof having a first chevron angle,

[0046] FIG. 6b is a schematic front view of the first heat exchanger plate according to an alternative embodiment, illustrating a corrugated pattern thereof having a first angle,

[0047] FIG. 7a is a schematic front view of the second heat exchanger plate according to one embodiment, illustrating a corrugated herringbone pattern thereof having a second chevron angle,

[0048] FIG. 7b is a schematic front view of the second heat exchanger plate according to an alternative embodiment, illustrating a corrugated pattern thereof having a second angle,

[0049] FIG. 8 is a schematic view of the first heat exchanger plate arranged on the second heat exchanger plate, illustrating contact points between them according to the example of FIG. 5,

[0050] FIG. 9 is a schematic view of the second heat exchanger plate arranged on the first heat exchanger plate, illustrating contact points between them according to the example of FIG. 5,

[0051] FIGS. 10a and 10b are a schematic plan views showing a refrigeration system according to various embodiments of the present invention in heating mode,

[0052] FIGS. 11a and 11b are a schematic plan views showing a refrigeration system according to FIGS. 10a and 11a in cooling mode,

[0053] FIG. 12 is an exploded perspective view of a heat exchanger to be fitted with a retrofit port heat exchanger according to one embodiment of the present invention,

[0054] FIG. 13 is a schematic perspective view of a retrofit port heat exchanger according to one embodiment,

[0055] FIG. 14 is a schematic perspective view of a retrofit port heat exchanger according to one alternative embodiment,

[0056] FIG. 15 is a schematic cross section view of a part of a heat exchanger comprising first and second heat exchanger plates according to another embodiment,

[0057] FIG. 16 is a schematic cross section view of a part of a heat exchanger comprising first and second heat exchanger plates according to another embodiment,

[0058] FIG. 17 is a schematic cross section view of a part of a heat exchanger comprising first and second heat exchanger plates according to yet another embodiment,

[0059] FIG. 18 is a schematic cross section view of a part of a stack of heat exchanger plates of first and second heat exchanger plates having different corrugation depths according to another embodiment,

[0060] FIG. 19 is a schematic exploded perspective view of a true dual heat exchanger according to one embodiment of the present invention, said heat exchanger comprising dual integrated suction gas heat exchangers, and

[0061] FIG. 20 is a schematic perspective view of another embodiment of the corrugated pattern of the heat exchanger plates, illustrating a corrugated pattern wherein the angle of the corrugated pattern in a central main heat exchanging section differs from the angle in sections at port openings of the heat exchanger plates.

DESCRIPTION OF EMBODIMENTS

[0062] With reference to FIG. 1 a brazed plate heat exchanger 100 is illustrated according to one embodiment, wherein a part thereof is illustrated more in detail in FIG. 2. The heat exchanger 100 comprises a plurality of first heat exchanger plates 110 and a plurality of second heat exchanger plates 120 stacked in a stack to form the heat exchanger 100. The first and second heat exchanger plates 110, 120 are arranged alternatingly, wherein every other plate is a first heat exchanger plate 110 and every other plate is a second heat exchanger plate 120. Alternatively, the first and second heat exchanger plates are arranged in another configuration together with additional heat exchanger plates. The heat exchanger 100 is an asymmetric plate heat exchanger.

[0063] The heat exchanger plates 110, 120 are made from sheet metal and are provided with a pressed pattern of ridges R1, R2a, R2b and grooves G1, G2a, G2b such that interplate flow channels for fluids to exchange heat are formed between the plates when the plates are stacked in a stack to form the heat exchanger 100 by providing contact points between at least some crossing ridges and grooves of neighbouring plates 110, 120 under formation of the interplate flow channels for fluids to exchange heat. The pressed pattern of FIGS. 1 and 2 is a herringbone pattern. However, the pressed pattern may also be in the form of obliquely extending straight lines. In any case, the pressed pattern of ridges and grooves is a corrugated pattern. The pressed pattern is adapted to keep the plates 110, 120 on a distance from one another, except from the contact points.

[0064] In the illustrated embodiment, each of the heat exchanger plates 110, 120 is surrounded by a skirt S, which extends generally perpendicular to a plane of the heat exchanger plate and is adapted to contact skirts of neighbouring plates in order to provide a seal along the circumference of the heat exchanger 100.

[0065] The heat exchanger plates 110, 120 are arranged with large port openings O1-O4 and small port openings SO1, SO2 for letting fluids to exchange heat into and out of the interplate flow channels. In the illustrated embodiment, the heat exchanger plates 110, 120 are arranged with a first large port opening O1, a second large port opening O2, a third large port opening O3 and a fourth large port opening O4. Further, the heat exchanger plates 110, 120 are arranged with a first small port opening SO1 and a second small port opening SO2. Areas surrounding the large port openings O1 to O4 are provided at different heights such that selective communication between the large port openings and the interplate flow channels is achieved. In the heat exchanger 100, the areas surrounding the large port openings O1-O4 are arranged such that the first and second large port openings O1 and O2 are in fluid communication with one another through some interplate flow channels, whereas the third and fourth large port openings O3 and O4 are in fluid communication with one another by neighboring interplate flow channels. In the illustrated embodiment, the heat exchanger plates 110, 120 are rectangular with rounded corners, wherein the large port openings O1-O4 are arranged near the corners. Alternatively, the heat exchanger plates 110, 120 are square, e.g. with rounded corners. Alternatively, the heat exchanger plates 110, 120 are circular, oval or arranged with other suitable shape, wherein the large port openings O1-O4 are distributed in a suitable manner. In the illustrated embodiment, each of the heat exchanger plates 110, 120 is formed with four large port openings O1-O4. In other embodiments of the invention, as described below, the number of large port openings may be larger than four, i.e. six, eight or ten. For example, the number of large port openings is at least six, wherein the heat exchanger is configured for providing heat exchange between at least three fluids. Hence, according to one embodiment, the heat exchanger is a three circuit heat exchanger having at least six large port openings and in addition being arranged with or without at least one integrated suction gas heat exchanger.

[0066] In the illustrated embodiment, each of the heat exchanger plates 110, 120 is formed with two small port openings SO1, SO2. The small port openings SO1, SO2 are arranged to provide an integrated suction gas heat exchanger. Hence, the first and second heat exchanger plates 110, 120 are formed with a dividing surface DW dividing the heat exchanger plates 110, 120 into a first heat exchanging portion 130 and a second heat exchanging portion 140, so that fluid passing between the first and second large port openings O1, O2 exchanges heat with fluids passing between third and fourth port openings O3, O4 over the first heat exchanging portion 130 of each plate 110, 120 and fluid passing between the first and second small port openings SO1, SO2 over the second heat exchanging portion 140 of each plate 110, 120.

[0067] The dividing surface DW is provided to divide the heat exchange area into the first heat exchanging portion 130 and the second heat exchanging portion 140. For example, the dividing surface DW is arranged between one long side of the heat exchanger plates 110, 120 and a neighbouring short side thereof. For example, the dividing surface DW extends all the way from the long side to the short side. Alternatively, the dividing surface DW is arranged between two long sides, and e.g. extends all the way from one long side to the other. In the illustrated embodiment, the dividing surface DW is curved between the long side and the short side of the plate. Alternatively, the dividing surface DW is straight or formed with a corner.

[0068] The dividing surface DW comprises an elongate flat surface provided on different heights of different plates 110, 120. When the flat surfaces of neighbouring plates 110, 120 contact one another to form the dividing surface DW, the interplate flow channel will be sealed, whereas it will be open if they do not. In the present case, the dividing surface DW is provided at the same height as the areas surrounding the first and second large port openings O1 and O2, meaning that for interplate flow channels fluidly connecting the first and second large port openings O1 and O2, the dividing surface DW will be open, whereas for the interplate flow channel fluidly connecting the third and fourth large port openings O3 and O4, the dividing surface DW will block fluid in this interplate flow channel.

[0069] Since the dividing surface DW will block fluid flow in the interplate flow channel communicating with the third and fourth large port openings O3 and O4, there will be separate interplate flow channels on either side of the dividing surface DW. The interplate flow channel on the side of the dividing surface DW not communicating with the third and fourth large port openings O3 and O4 communicates with the two small port openings SO1 and SO2. It should be noted that the dividing surface DW does not block the interplate flow channels communicating with the first and second large port openings O1 and O2; hence, medium flowing in the interplate flow channels communicating with the small port openings SO1 and SO2 will exchange heat with medium flowing in the flow channels communicating with the first and second large port openings O1 and O2—just like medium flowing in the interplate flow channels communicating with the third and fourth large port openings O3 and O4.

[0070] In the embodiment shown in FIGS. 1 and 2, the dividing surface DW extends between the first large port opening O1 and the third large port opening O3. The small openings SO1 and SO2 are situated on either sides of the first large port opening O1. It should be noted that the first large port opening O1 is placed such that medium flowing in the interplate flow channel communicating with the small port openings SO1 and SO2 may pass on both sides of the first large port opening O1. The dividing surface DW extends between the first large port opening O1 and the remaining large port openings O2-O4, wherein the first and second small openings SO1, SO2 are on the same side of the dividing surface DW as the first large port opening O1, i.e. in the second heat exchanging portion 140, and the other large port openings O2-O4 are arranged on the other side of the dividing surface DW, i.e. outside the dividing wall DW and in the first heat exchanging portion 130.

[0071] In the illustrated embodiment, the heat exchanger 100 comprises only the first and second heat exchanger plates 110, 120. Alternatively, the heat exchanger 100 comprises a third and optionally also a fourth heat exchanger plate, wherein the third and optional fourth heat exchanger plates are arranged with different pressed patterns than the first and second heat exchanger plates 110, 120, and wherein the heat exchanger plates are arranged in a suitable order.

[0072] In the illustrated embodiment, the heat exchanger 100 also comprises a start plate 150 and an end plate 160. The start plate 150 is formed with openings corresponding to the large port openings O1-O4 and the small port openings SO1, SO2 for letting fluids into and out of the interplate flow channels formed by the first and second heat exchanger plates 110, 120. For example, the end plate 160 is a conventional end plate.

[0073] With reference to FIG. 3, a section view of the first heat exchanger plate 110 according to one embodiment is illustrated schematically. The first heat exchanger plates 110 are formed with a first pattern of ridges R1 and grooves G1. The grooves G1 of the first heat exchanger plates are formed with identical depth D1, which is illustrated schematically in FIG. 3. Hence, all grooves G1 are formed with the same depth D1. For example, the depth D1 is 0.5-5 mm, such as 0.6-3 mm or 0.8-3 mm. For example, all ridges R1 are formed with the same height in a corresponding manner. In other words, the corrugation depth of the first heat exchanger plates 110 is symmetrical and similar throughout the plate or at least substantially throughout the plate. According to one embodiment, at least the first heat exchanging portion 130 of the first heat exchanger plate 110, such as the entire first heat exchanging portion 130 thereof, is formed with identical corrugation depth, wherein each of the grooves G1 is formed with the depth D1. For example, the first heat exchanging portion 130 and the second heat exchanging portion 140 of the first heat exchanger plate 110, such as the entire first heat exchanging portion 130 and the entire second heat exchanging portion, is formed with identical corrugation depth, wherein each of the grooves G1 is formed with the depth D1.

[0074] With reference to FIG. 4, a section view of the second heat exchanger plate 120 is illustrated schematically according to one embodiment. For example, all second heat exchanger plates 120 are identical. The second heat exchanger plates 120 are formed with a second pattern of first and second ridges R2a, R2b and first and second grooves G2a, G2b. The first and second grooves G2a, G2b of the second heat exchanger plates 120 are formed with different depths, wherein the first grooves G2a are formed with a first depth D2a, and the second grooves G2b are formed with a second depth D2b, wherein the second depth D2b is different from the first depth D2a. For example, the first depth D2a is 0.5-5 mm, such as 0.6-3 mm or 0.8-3 mm, wherein the second depth D2b is 30-80% of the first depth D2a, such as 40-60% thereof. The ridges R2a, R2b have different heights in a corresponding manner. In the illustrated embodiment, the first depth D2a is larger than the second depth D2b. The first and second grooves G2a, G2b are arranged alternatingly. Alternatively, the first and second grooves G2a, G2b, and optionally further grooves having other depths, are arranged in any desired pattern.

[0075] For example, the pattern of ridges and grooves of the second heat exchanger plates 120 is asymmetrical, i.e. the second heat exchanger plates 120 forms an asymmetric heat exchanger when combined with first heat exchanger plates 110 such as shown below with reference to FIG. 5. According to one embodiment, at least the first heat exchanging portion 130 of the second heat exchanger plate 120, such as the entire first heat exchanging portion 130 thereof, is formed with the second pattern of ridges and grooves having at least two different corrugation depths D2a, D2b of the grooves. For example, the first heat exchanging portion 130 and the second heat exchanging portion 140 of the first heat exchanger plate 110, such as the entire first heat exchanging portion 130 and the entire second heat exchanging portion, is formed with at least two corrugation depths, wherein the first grooves G2a are formed with the first depth D2a, and the second grooves G2b are formed with the second depth D2b.

[0076] With reference to FIG. 5 a plurality of the first and second heat exchanger plates 110, 120 have been stacked to schematically illustrate formation of interplate flow channels according to one embodiment. In the illustrated embodiment, every other plate is a first heat exchanger plate 110 and the remaining plates are second heat exchanger plates 120, wherein the first and second heat exchanger plates are arranged alternatingly to form an asymmetric heat exchanger 100, wherein the interplate flow channels are formed with different volumes. Alternatively, the different volumes of the interplate flow channels are formed by an extended profile on the same press depth or corrugation depth. For example, the first and second heat exchanger plates are provided with different corrugation depths. For example, the first and/or second heat exchanger plates is/are asymmetric heat exchanger plates. Alternatively, the first and/or second heat exchanger plates is/are symmetric heat exchanger plates.

[0077] With reference to FIG. 6a the first pattern of ridges R1 and grooves G1 of the first heat exchanger plate 110 is illustrated schematically. Said pattern is a pressed herringbone pattern, wherein the ridges R1 and grooves G1 are arranged with two inclined legs meeting in an apex, such as a centrally arranged apex, to form an arrow shape. For example, the apices are distributed along an imaginary centre line, such as a longitudinal centre line of a rectangular heat exchanger plate. For example, the herringbone pattern is arranged so that ridges R and grooves G, at least in a central portion of the first heat exchanger plate 110, extend from one long side to the other of the first heat exchanger plate 110, e.g. with all the apices pointing towards one of the short sides. The pattern of the first heat exchanger plate 110, i.e. the first pattern of ridges R1 and grooves G1, exhibits a first chevron angle (31. The chevron angle is the angle between the ridge and an imaginary line across the plate, perpendicular to the long sides of a rectangular plate, which is illustrated schematically by means of the dashed line C. Hence, the chevron angle is the angle between the ridge and a short side of the heat exchanger plate towards which the apex is pointing. The long sides of the heat exchanger plates extend perpendicular to the short sides and hence the pattern of ridges and grooves is also arranged so that the ridges have an angle to the long sides. For example, the chevron angle is the same on both sides of the apex. For example, the entire or substantially entire first pattern of ridges and grooves is formed with the first chevron angle β1 throughout the plate or at least throughput the first heat exchanging portion 130, and for example also the second heat exchanging portion 140. For example, the first chevron angle β1 is 25° to 70° or 30° to 45°.

[0078] With reference to FIG. 6b the first pattern of ridges R1 and grooves G1 of the first heat exchanger plate 110 is illustrated schematically according to an alternative embodiment, wherein the pressed pattern is in the form of obliquely extending straight lines. Hence, the pressed pattern of ridges and grooves is a corrugated pattern of obliquely extending straight lines. The obliquely extending straight lines of the first heat exchanger plates 110 are arranged in the angle β1. For example, the pattern is arranged so that ridges R1 and grooves G1 extend, e.g. in parallel, from one long side to the other of the first heat exchanger plate 110.

[0079] With reference to FIG. 7a the second pattern of ridges R2a, R2b and grooves G2a, G2b of the second heat exchanger plate 120 is illustrated schematically. Said second pattern is a pressed herringbone pattern as described above with reference to the first heat exchanger plate 110 but with a second chevron angle β2 different from the first chevron angle β1. Hence, the second heat exchanger plate 120 is arranged with a herringbone pattern having a different angle than the first heat exchanger plate. For example, the second chevron angle β2 is 0° to 90°, 25° to 70° or 30° to 45°. For example, the entire or substantially entire pattern of ridges and grooves of the second heat exchanger plates 120 is formed with the second chevron angle β2 throughout the plate or at least throughput the first heat exchanging portion 130, and for example also the second heat exchanging portion 140. For example, a difference between the first and second chevron angles β1 and β2 is 2° to 35°.

[0080] With reference to FIG. 7b the second pattern of ridges R2a, R2b and grooves G2a, G2b of the second heat exchanger plate 120 is illustrated schematically according to an alternative embodiment, wherein the pressed pattern is in the form of obliquely extending straight lines. Hence, the pressed pattern of ridges and grooves is a corrugated pattern of obliquely extending straight lines. The obliquely extending straight lines of the second heat exchanger plates 120 are arranged in the angle β2. For example, the pattern is arranged so that ridges R2a, R2b and grooves G2a, G2b extend, e.g. in parallel, from one long side to the other of the second heat exchanger plate 120

[0081] Hence, the first and second heat exchanger plates 110, 120 are formed with different chevron angles β1, β2 and different pressed patterns resulting in different interplate volumes. For example, the first and second heat exchanger plates 110, 120 are provided with different corrugation depths. Alternatively or in addition, the first and second heat exchanger plates 110, 120 are provided with different corrugation frequencies. For example, the first and second heat exchanger plates 110, 120 are provided with the same corrugation depth but different corrugation frequencies. Hence, the first and second heat exchanger plates 110, 120 are provided with different corrugation depths and/or different corrugation frequencies. For example, one of the first and second heat exchanger plates 110, 120 is a symmetric heat exchanger plate, wherein the other is asymmetric. Alternatively, both the first and second heat exchanger plates 110, 120 are asymmetric. Alternatively, both the first and second heat exchanger plates 110, 120 are symmetric.

[0082] In FIGS. 8 and 9 contact points between the first and second plates 110, 120 are illustrated schematically using the example of FIG. 5. In and/or around the contact points 170 between crossing ridges and grooves brazing joints 170 are formed. In the embodiment of FIGS. 8 and 9 brazing joints 170 are formed an all contact points. Alternatively, brazing joints 170 are formed in only some of the contact points. In FIG. 8 the first heat exchanger plate 110 is arranged on the second heat exchanger plate 120, wherein contact points are formed in a first pattern. In FIG. 8 all crossings between the ridges R1 of the first heat exchanger plate 110 and ridges or grooves of the second heat exchanger plate 120 result in a contact point.

[0083] FIG. 9 is a schematic view of the second heat exchanger plate 120 arranged on the first heat exchanger plate 110, wherein contact points are formed in a second pattern. In FIG. 9 only crossings between the first ridges R2a of the second heat exchanger plate 120 result in a contact point, which may form a brazing joint 170, wherein the second ridges R2b are arranged with a gap to the crossing ridges or grooves of the first heat exchanger plate 110. Hence, and no contact points are formed, and no brazing joint is formed, between the second ridges R2b of the second heat exchanger plate 120 and the first heat exchanger plate 110. In FIG. 9 all contact points are showed with a brazing joint 170.

[0084] According to one embodiment, the brazing joints 170 between the first and second heat exchanger plates 110, 120 are elongated, such as oval, wherein the brazing joints 170 are arranged in a first orientation in the interplate flow channels having bigger volume and in a second orientation in the interplate flow channels having smaller volume to provide a favourable pressure drop in the desired interplate flow channels. For example, the brazing joints 170 are arranged in a first angle in relation to a longitudinal direction of the plates 110, 120 in the interplate flow channels having bigger volume and in a second angle in the remaining interplate flow channels. According to one embodiment, the first angle is bigger than the second angle.

[0085] In FIGS. 10a, 10b and 11a, 11b, embodiments of a chiller system that can use a heat exchanger 100 according to any of the above heat exchanger embodiments is shown in in heating mode and cooling mode, respectively. Chiller system can also be called refrigeration system.

[0086] The chiller system according to embodiments of FIGS. 10a, 10b, 11a, 11b comprises a compressor C, a four-way valve FWV, a payload heat exchanger PLHE connected to a brine system requiring heating or cooling, a first controllable expansion valve EXPV1, a first one-way valve OWV1, a dump heat exchanger DHE connected to a heat source to which undesired heat or cold could be dumped, a second expansion valve EXPV2 and a second one-way valve OWV2. The heat exchangers PLHE and DHE are each provided with the four large openings O1-O4 as disclosed above and the two small openings SO1 and SO2, wherein the large openings O1 and O2 of each heat exchanger communicate with one another, the large openings O3 and O4 of each heat exchanger communicate with one another and wherein the small openings SO1 and SO2 of each heat exchanger communicate with one another. Heat exchange will occur between fluids flowing from O1 to O2 and fluids flowing between O3 and O4 and SO1 and SO2. There will, however, be no heat exchange between fluids flowing from O3 to O4 and fluids flowing from SO1 to SO2. The payload heat exchanger PLHE and/or the dump heat exchanger DHE is/are a plate heat exchanger 100 as described herein.

[0087] In heating mode, shown in FIGS. 10a and 10b, the compressor C will deliver high pressure gaseous refrigerant to the four-way valve FWV. In this heating mode, the four-way valve is controlled to convey the high pressure gaseous refrigerant to the large opening O1 of the payload heat exchanger PLHE. The high pressure, gaseous refrigerant will then pass the payload heat exchanger PLHE and exit at the large opening O2. While passing the pay-load heat exchanger PLHE, the high pressure gaseous refrigerant will exchanger heat with a brine solution connected to a pay-load requiring heating and flowing from the large opening O4 to the large opening O3, i.e. in a counterflow direction compared to the refrigerant, which flows from the large opening O1 to the large opening O2. While exchanging heat with the brine solution, the high pressure gaseous refrigerant will condense, and when exiting the Pay-load heat exchanger PLHE through the large opening O2, it will be fully condensed, i.e. be in the liquid state.

[0088] In the heating mode, the first expansion valve EXPV1 will be fully closed, and the flow of liquid refrigerant exiting the pay-load heat exchanger will pass the first one-way valve OWV1, which allows for a refrigerant flow in this direction, while it will block flow in the other direction (which will be explained later in connection to the description of the cooling mode).

[0089] After having passed the first one-way valve OWV1, the liquid refrigerant (still comparatively hot) will enter the small opening SO2 of the dump heat exchanger DHE and exit the heat exchanger through the small opening SO1. During the passage between the small openings SO and SO1, the temperature of the refrigerant will drop significantly due to heat exchange with cold, primarily gaseous refrigerant about to exit the dump heat exchanger DHE.

[0090] During e.g. a cold start, i.e. before the system has reached a favourable running condition, it might be necessary to balance the amount of heat exchange in the suction gas heat exchanger. This can be achieved by controlling a balance valve BV, the balance valve BV being e.g. a three-way valve arranged to enable control of liquid refrigerant from the condenser to either, or both, of the small opening SO2 and the expansion valve EXPV2, hence controlling the amount of heat exchange in the suction gas heat exchanger.

[0091] After leaving the dump heat exchanger DHE through the small opening SO1, the liquid refrigerant will pass the second expansion valve EXPV2, where the pressure of the refrigerant will drop, causing flash boiling of some of the refrigerant, which will cause the temperature to drop. From the second expansion valve, the refrigerant will pass a branch connected to both the second one-way valve OWV2, which is connected between the high pressure side and the low pressure side of the refrigerant circuitry and closed for refrigerant flow due to the pressure difference between the high pressure side and the low pressure side. After having passed the branch, the cold, low pressure semi liquid refrigerant will enter the large opening O2 and pass the dump heat exchanger DHE under heat exchange with a brine solution connected to a source from which low temperature heat can be collected, e.g. an outside air collector, a solar collector or a hole drilled in the ground. Due to the heat exchange with the brine solution, which flows from the large opening O4 to the large opening O3, the primarily liquid refrigerant will vaporize. The heat exchange between the brine solution and the refrigerant will take place under co-current conditions, which is well known to give an inferior heat exchange performance as compared to counter-current heat exchange.

[0092] Just prior to the exiting the dump heat exchanger DHE through the large opening O1, the refrigerant (now almost completely vaporized) will exchange heat with the comparatively hot, liquid refrigerant that entered the dump heat exchanger through the small opening SO2 and exited the dump heat exchanger through the small port opening SO1. According to one embodiment of the invention, about 85-98, preferably 90-95 and more preferably 91-94, e.g. 93 percent of the refrigerant is vaporized when it starts exchange heat with the hot liquid refrigerant.

[0093] Consequently, the temperature of the refrigerant about to exit the dump heat exchanger DHE through the opening O1 will increase, hence ensuring that all of this refrigerant is completely vaporized.

[0094] Hence, the low temperature gaseous refrigerant entering the suction gas heat exchanger contains a certain amount of low temperature liquid refrigerant, said low temperature liquid refrigerant vaporizing as a result of the heat exchange with the high temperature liquid refrigerant from the condenser. For example, said certain amount of low temperature liquid refrigerant amounts to 2-15, preferably 5-10, more preferably 6-9 and for example 7 percent by mass.

[0095] It is well known by persons skilled in the art that co-current heat exchange is inferior to counter-current heat exchange when it comes to the heat exchange performance. However, due to the provision of the heat exchange between the relatively hot liquid brine entering the small opening SO2 and the mainly gaseous refrigerant about to leave the dump heat exchanger DHE (i.e. a so-called “suction gas heat exchange”), it is not necessary to vaporize the refrigerant completely during the brine-refrigerant heat exchange. Instead, the refrigerant may be only semi-vaporized when it enters the suction gas heat exchange with the hot liquid refrigerant, since the remaining liquid phase refrigerant will evaporate during this heat exchange. It is well known that liquid-to-liquid heat exchange is much more efficient than gas-to-liquid heat exchange. Also, co-current heat exchange has the additional benefit that the risk of freezing is reduced, since the refrigerant enters the heat exchanger on a position where the medium with which the refrigerant shall exchange heat has a high temperature, hence reducing the risk of freezing at this position, which is the most critical position for freezing.

[0096] Tests have shown that there might be a problem with cold-starting the chiller system in cold environments.

[0097] From the opening O1 of the dump heat exchanger, the gaseous refrigerant will enter the four-way valve FWV, which is controlled to direct the flow of gaseous refrigerant to the compressor, in which the refrigerant is compressed again.

[0098] In FIG. 11a, 11b, the chiller system is shown in cooling mode. In order to switch mode from heating mode to cooling mode, the four-way valve FWV is controlled such that the compressor feeds compressed gaseous refrigerant to the opening O1 of the dump heat exchanger DHE. The expansion valve EXPV2 will be entirely closed, the one-way valve OWV2 will be open, the one-way valve OWV1 will be closed and the expansion valve EXPV1 will be open to control the pressure before and after the refrigerant has passed the expansion valve EXPV1.

[0099] Hence, in cooling mode, the dump heat exchanger will function as a counter-current condenser, and the “suction gas heat exchanger” thereof will not perform any heat exchange, whereas the pay-load heat exchanger PLHE will function as a co-current evaporator. However, due to the provision of the suction gas heat exchange between the hot liquid refrigerant and semi-vaporised refrigerant about to leave the pay-load heat exchanger PLHE, the efficiency of the co-current heat exchange can be maintained at acceptable levels.

[0100] It should be noted that the suction gas heat exchanging parts are integrated with the dump heat exchanger DHE and the pay-load heat exchanger PLHE in FIGS. 10a, 10b and 11a, 11b. In other embodiments, however, the suction gas heat exchangers may be separated from the dump heat exchanger and/or the pay-load heat exchanger.

[0101] In different climate zones, there are different needs for cooling and heating. In a warmer climate there is a larger need for cooling, wherein the refrigeration system will be used closer to the full cooling effect and a corresponding capacity in the suction gas heat exchanger is required to evaporate any droplets that otherwise would exit the evaporator. For example, the evaporator is the pay-load heat exchanger PLHE in cooling mode of the refrigeration system as described above, wherein the integrated suction gas heat exchanger thereof is used accordingly by means of the balance valve BV, which may be the same or another balance valve as illustrated schematically in FIG. 11b. When the refrigeration system is used at reduced effect, such as at 25% or 50% of the full effect, the suction gas heat exchanger is controlled through the balance valve BV. The refrigeration system is reversible and can be switched between cooling mode and heating mode by the four-way valve FWV as described above. As illustrated in the drawings, both the pay-load heat exchanger and the dump heat exchanger comprises an integrated suction gas heat exchanger which can be activated and controlled by the balance valve BV to ensure evaporation of the refrigerant before exiting the evaporator in both cooling mode and heating mode and with zero superheat in accordance with the effect at which the system is running. Hence, the amount of refrigerant conducted to the suction gas heat exchanger can be adapted to the system conditions in both heating mode and cooling mode to provide an efficient reversible refrigeration system for different types of climates.

[0102] In another embodiment of the invention, a “standard” heat exchanger 100, such as for example shown in FIG. 12 may be provided with a retrofit port heat exchanger 400 (see FIGS. 13 and 14) comprising some kind of structure that fits in or just outside a port opening O1-O4 of the standard heat exchanger.

[0103] In the shown embodiment, the retrofit port heat exchanger 400 comprises a pipe 410 that suits within the port opening, said pipe being bent in a semi helix for allowing high temperature liquid refrigerant flowing therein in the same way as refrigerant flowing between the small port openings SO1 and SO2 of the previously described embodiments exchanges heat with cold, gaseous (or semi gaseous) refrigerant about to leave the dump heat exchanger DHE or the pay load heat exchanger PLHE.

[0104] With reference to FIG. 15 a cross section of a part of a heat exchanger comprising first and second heat exchanger plates 110, 120 according to another embodiment is illustrated schematically. In the embodiment of FIG. 15 the first heat exchanger plate 110 is a symmetric heat exchanger plate, wherein the second heat exchanger plate 120 is an asymmetric heat exchanger plate as described above. Hence, the corrugation depth of the first heat exchanger plate 110 is constant, wherein the corrugation depth of the second heat exchanger plate 120 is varying. The second heat exchanger plate 120 is formed with at least two different corrugation depths. Also, the first and second heat exchanger plates 110, 120 are formed with corrugated patterns different angles, such as chevron angles, as described above. In the embodiment of FIG. 15 the chevron angle of the first heat exchanger plate 110 is 54 degrees, wherein the chevron angle of the second heat exchanger plate 120 is 61 degrees. For example, neighbouring interplate volumes are different, so that the interplate volume on one side of the first heat exchanger plates 110 is different from the interplate volume on the opposite side of the first heat exchanger plates 110. Of course, this also apply for the second heat exchanger plates 120. Hence, the interplate volume between the first and second heat exchanger plates is different from the interplate volume between the second and first heat exchanger plates. Similarly, a cross section area on one side of the first heat exchanger plates 110 is different from the cross section area on the opposite side of the first heat exchanger plates 110.

[0105] With reference to FIG. 16 a cross section of a part of a heat exchanger comprising first and second heat exchanger plates 110, 120 according to yet another embodiment is illustrated schematically. In the embodiment of FIG. 16 the first heat exchanger plate 110 is a symmetric heat exchanger plate, wherein the second heat exchanger plate 120 is an asymmetric heat exchanger plate as described above. In the embodiment of FIG. 16 the chevron angle of the first heat exchanger plate 110 is 45 degrees, wherein the chevron angle of the second heat exchanger plate 120 is 61 degrees.

[0106] With reference to FIG. 17 a cross section of a part of a heat exchanger comprising first and second heat exchanger plates 110, 120 according to yet another embodiment is illustrated schematically. In the embodiment of FIG. 17 the first heat exchanger plate 110 is an asymmetric heat exchanger plate, wherein the second heat exchanger plate 120 is also an asymmetric heat exchanger plate. In the embodiment of FIG. 17 the chevron angle of the first heat exchanger plate 110 is different from the chevron angle of the second heat exchanger plate 120 as described above. Also, the interplate flow channels have different volumes as described above. For example, the brazing joints are elongated, such as oval, and arranged in a first orientation in the interplate flow channels having bigger volume and in a different, second orientation in the interplate flow channels having smaller volume.

[0107] With reference to FIG. 18 a cross section of a part of a stack of first and second heat exchanger plates 110, 120 according to yet another embodiment is illustrated schematically. In the embodiment of FIG. 18 the first and second heat exchanger plates 110, 120 are provided with different corrugation depths. The first heat exchanger plate 110 is a symmetric heat exchanger plate, wherein the second heat exchanger plate 120 is an asymmetric heat exchanger plate. Alternatively, both the first and second heat exchanger plates 110, 120 are symmetric or asymmetric. The chevron angle of the first heat exchanger plate 110 is different from the chevron angle of the second heat exchanger plate 120 and the interplate flow channel volumes formed by the first and second heat exchanger plates 110, 120 when brazed together in brazing joints are different.

[0108] The heat exchanger according to various embodiments of the present invention is, e.g. used for condensation or evaporation, wherein at least one media at some point is in gaseous phase. For example, the heat exchanger is used for heat exchange, wherein condensation or evaporation takes place in the interplate flow channels of bigger volume. For example, a liquid media, such as water or brine, is conducted through the interplate flow channels having smaller volume.

[0109] In FIG. 19, an exemplary brazed true-dual heat exchanger 500 comprising two separate integrated suction gas heat exchangers ISGHX1 and ISGHX2 is shown in an exploded view. True-dual heat exchangers are used for heat-pumps or chillers where a large power ratio is required. Systems for true-dual heat exchangers are well known for people skilled in the art—they generally consist of two separate heat pump systems using a true-dual heat exchanger rather than two separate heat exchangers.

[0110] The true-dual heat exchanger 500 comprises six heat exchanger plates 510, 520, 530 and 540. Each of the heat exchanger plates is provided with a pressed pattern of ridges and grooves adapted to keep the plates on a distance from one another such that interplate flow channels 510-520, 520-530, 530-540, 540-510, 510-520 for media to exchange heat are formed between the heat exchanger plates. Also, each of the heat exchanger plates is provided with port openings 550, 560, 570, 580, 590, 600, 610 for refrigerant and two port openings 620, 630 for water or brine solution. The port openings are in selective fluid communication with the interplate flow channels in the following manner:

[0111] The port openings 630 and 640 are in fluid communication with the interplate flow channels 510-520 and 530-540, the port openings 550 and 560 are in fluid communication with the interplate flow channels 520-530, the port openings 570 and 580 are in fluid communication with the interplate flow channels 540-510, and the port openings 590, 600,610 and 620 are in fluid communication with the interplate flow channels 510-520.

[0112] The heat exchanger plates 510, 520, 530 and 540 are divided into subsections wherein the interplate flow channels are connected and restricted in certain ways: in a main section 650, all interplate flow sections are used for media to exchange heat; in a first isghx (integrated suction gas heat exchanger) section ISGHX1, the interplate flow channels 520-530 are fluidly connected to the interplate flow channel 520-530 of the main section and either or both of the interplate flow channels 510-520 and/or 530-540 are connected to the port openings 610 and 620; and in a second isghx section ISGHX2, the interplate flow channels 540-510 are fluidly connected to the interplate flow channels 540-510 of the main section and either or both of the interplate flow channels 510, 520 and/or 530-540 are fluidly connected to the port openings 590, 600.

[0113] The main section is delimited from the isghx sections ISGHX1 and ISGHX2 by a dividing wall 660, which extends from one long side of each heat exchanger plate to the other long side. The dividing wall comprises plate surfaces arranged on different heights such that cooperation between such plate surfaces of neighbouring plates seals off the interplate flow channels 510-520 and 530-540 from communication with the corresponding interplate flow channels of the isghx sections ISGHX1 and ISGHX2. Moreover, the plate surfaces of the dividing wall 660 are configured such that cooperation between the plate surfaces of neighbouring plates seal off communication between the interplate flow channel 520-530 of the main section and the corresponding interplate flow channel of the second isghx section ISGHX2 and seals off communication between the interplate flow channel 540-510 of the main section and the corresponding interplate flow channels of the first isghx section ISGHX1. The dividing wall 660 divides the heat exchanger plates 510-540 into the main section 650 and the isghx subsections ISGHX1 and ISGHX2. Hence, four of the port openings are arranged in the main section 650, i.e. the port openings 550, 570, 630 and 640, wherein the port openings 560 and 580 along with the first and second isghx sections ISGHX1 and ISGHX2 with the port openings 610, 620, 590, 600 are arranged on the other side of the dividing wall 660.

[0114] A second dividing wall 670 is provided between the isghx sections ISGHX1 and ISGHX2 and extends from a short side of the heat exchanger plates and the dividing wall 660. Plate surfaces of this dividing wall are arranged such that plate surfaces of neighbouring plates contact one another for sealing off all interplate flow channels of the isghx sections ISGHX1 and ISGHX2 from communication with one another. Hence, the port opening 560 and the first isghx section with the port openings 610 and 620 are arranged on one side of the dividing wall 670, wherein the port opening 580 and the second isghx section with the port openings 590 and 600 are arranged on the other side of the dividing wall 670. Hence, the main section 650m the first isghx section ISGHX1 and the second isghx section ISGHX2 are separated by the dividing walls 660, 670

[0115] Finally, each of the heat exchanger plates are provided with a skirt 680 that extends around the entire periphery of the heat exchanger plates 510, 520, 530, 540, the skirts 680 of neighbouring plates being adapted to contact one another in order to create a circumferential seal stopping media from escaping the interplate flow channels. Moreover, the heat exchanger 500 according to the invention is preferably provided with a start and/or end plate (not shown), which are/is arranged on either sides of he stack of heat exchanger plates. Either of the start or end plate is provided with port openings, while the other is not, in order to create for a seal on the side of the port opening that is not provided with a connection for letting fluid to exchange heat in or out from the heat exchanger.

[0116] By the above arrangement, a true-dual heat exchanger having separate interplate flow channels between port openings 630 and 640 over the interplate flow channels 510-520 and 530-540 of the main section 650, between port openings 550 and 560 over the interplate flow channel 520-530 of the main section and the first isghx section ISGHX1, between port openings 570 and 580 over the interplate flow channel 540-510 of the main section 650 and the second isghx section ISGHX2, between port openings 610 and 620 over the interplate flow channel 520-530 of the first isghx section ISGHX1 and between port openings 590 and 600 over the interplate flow channel 540-510 of the second isghx section ISGHX2, respectively.

[0117] The selective fluid communication between the port openings and the interplate flow channels can be achieved in a number of ways, e.g. by providing surfaces around the port openings on different heights, such that the surfaces of neighbouring plates contact one another or do not contact one another. Alternatively, the selective fluid communication can be achieved by providing separate sealing rings in the port openings, said sealing rings being provided with openings for allowing communication where desired.

[0118] Also, it should be noted that although described as a brazed heat exchanger, it is possible to design a true-dual heat exchanger according to the invention as a gasketed heat exchanger.

[0119] The true-dual heat exchanger 500 according to the present invention is especially useful for heat pump or chiller applications wherein dual compressors are used in order to attain a large ratio between a low power and a high power.

[0120] The heat exchanger plates 510-540 are provided with the first and second patterns of ridges R1, R2a, R2b and grooves G1, G2a, G2b as described above with reference to FIGS. 2-9. For example, every other heat exchanger plate is provided with the first pattern, wherein the other heat exchanger plates are provided with the second pattern. For example, the heat exchanger plates 510, and 530 are provided with the first pattern, wherein the heat exchanger plates 520, 540 are provided with the second pattern or vice versa. The pressed first and second patterns are, e.g. herringbone patterns with different chevron angles or pressed patterns of oblique lines with different angles as described above, such as described with reference to FIGS. 6a, 6b, 7a, and 7b. The main sections 650 are provided with such patterns and, e.g. also the first and second isghx sections ISGHX1 and ISGHX2 are provided with such patterns. For example, the angle β1, such as the chevron angle β1, of every other heat exchanger plate, such as the heat exchanger plates 510, 530, is 25° to 70° or 30° to 45°. For example, the angle β2, such as the chevron angle β2, of every other heat exchanger plate, such as the heat exchanger plates 520, 540, is 25° to 70° or 30° to 45°. The first and second patterns are in opposite directions, so that the angles or chevron apices alternatingly are in opposite directions throughout the heat exchanger. For example, the difference between the first and second chevron angles β1 and β2 is 2° to 35°.

[0121] For example, the grooves G1 of every other heat exchanger plate are formed with identical depth D1, as described with reference to FIG. 3, wherein the other heat exchanger plates having the first and second grooves G2a, G2b are formed with different depths, wherein the first grooves G2a are formed with a first depth D2a, and the second grooves G2b are formed with a second depth D2b as described with reference to FIG. 4. Hence, every other interplate flow channel has bigger volume than the rest as also described above.

[0122] For example, the contact points and brazing joints are alternatingly arranged as described with reference to FIGS. 8 and 9, so that the brazing joints between the heat exchanger plates 510-540 are elongated, such as oval, wherein the brazing joints are arranged in a first orientation in the interplate flow channels having bigger volume and in a second orientation in the interplate flow channels having smaller volume.

[0123] With reference to FIG. 20 the first pattern of ridges R1 and grooves G1 of the first heat exchanger plate 110 is illustrated schematically. In FIG. 20 the first heat exchanger plate 110 comprises the small port openings SO1, SO2 and the dividing surface DW to provide the first heat exchanging portion 130 and the second heat exchanging portion 140 forming the integrated suction gas heat exchanger as described above. Alternatively, the first heat exchanger plate 110 comprises the dividing walls 660, 670 and the small port openings 590-620 to provide the two integrated suction gas heat exchangers ISGHX1, ISGHX2 as described with reference to FIG. 19. The pressed pattern according to the embodiment of FIG. 20 is a herringbone pattern but may alternatively be a pattern of oblique lines and thus exhibits the first angle β1 generally as described above with reference to FIGS. 6a and 6b but in a central main heat exchanging section of the heat exchanger plate 110. Hence, the first pressed pattern partially comprises the first angle β1. For example, the central main heat exchanging section extends across the first heat exchanger plate 110 from one side to the opposite side. The central main heat exchanging section is arranged between first and second heat exchanging sections at port openings of the heat exchanger plate, called end sections herein. The first and second end sections are, for example, arranged at opposite ends of the first heat exchanger plate 110. For example, the first and second end sections extend across the first heat exchanger plate 110 from one side to the opposite side thereof. The first end section includes port openings, such as the first port opening O1 and the third port opening O3, and the small port openings SO1, SO2 and the dividing surface DW forming the suction gas heat exchanger. The second end section includes port openings, such as the second and fourth port openings O2, O4. The pressed pattern of ridges and grooves R1, G1 is arranged with an angle β1′ in at least one end section, such as the first and second end sections, which angle β1′ differs from the angle β1 of the pressed pattern in the central main heat exchanging section. For example, the direction of the pressed pattern is the same in the central main section as in the end sections. For example, the angle is the same in both end sections. Alternatively, the angle in the first end section is different from the angle in the second end section. Optionally, the second heat exchanging portion 140 is arranged with a pattern or an angle different from the first end section. In FIG. 20 the first heat exchanger plate 110 is illustrated as an example but it is understood that the second pressed pattern of the second heat exchanger plate 120 is designed in a corresponding manner, wherein the second pattern of ridges R2a, R2b and grooves G2a, G2b is arranged with the angle β2 in the central main heat exchanging section and the end sections are arranged with a different angle β2′ (not illustrated).