MXPA98005396A - Heat exchangers pl - Google Patents

Abstract

The present invention relates to improvements in plate heat exchangers, and particularly relates to improvements in these heat exchangers, using as evaporators in cooling systems

Description

PLATE HEAT EXCHANGERS DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to improvements in plate heat exchangers, and particularly relates to improvements in these heat exchangers, used as evaporators in refrigeration systems.

BACKGROUND Plate heat exchangers have been developed for use in refrigeration systems and are extremely effective and efficient in transferring heat from a heat exchange fluid, such as water, to the refrigerant. These heat exchangers include a set of a plurality of metal plates, which are formed, by stamping, with a series of edges and channels. The edges and channels, in the set, constitute trajectories for the refrigerant, and for a heat exchange fluid. The refrigerant and the heat exchange fluid pass through the heat exchanger on the opposite sides of each plate, having coolant inlet openings and heat exchange fluid outlet openings at one end of the heat exchanger, and corresponding openings of exit and entrance at the other end of the heat exchanger. When plate heat exchangers are used as evaporators in the refrigeration systems, difficulties are often experienced to ensure uniform distribution of the refrigerant in the heat exchanger, and the multitude of passages between the plates. In general terms, the refrigerant, before entering the heat exchanger, is extended through an expansion valve or refrigerant pressure reducing device, immediately before entering the heat exchanger, however, an irregular mixture is produced of liquid and vapor in the refrigerant that enters the heat exchanger. It will be understood that liquid refrigerant passing through an expansion device, or pressure reducing device, causes some of the refrigerant to evaporate during the expansion or pressure reduction phase. The amount of vaporization depends on the temperature of the liquid refrigerant before the expansion device, and the degree of expansion or reduction of pressure. Expansion rates of 50: 1 can be experienced, resulting in up to 2 percent or more of vaporization of the liquid during the expansion or pressure reduction phase. Since steam can count on 50 percent or more of the volumetric area occupied by the mixture of liquid refrigerant and vapor, and since the liquid and gas refrigerant has different densities that give rise to variable flow patterns, some passages Within a system of heat exchange plates, they will receive more liquid refrigerant than others. Accordingly, this results in an irregularity in the relative amounts of liquid and vapor that pass through the different passages of coolant, thereby resulting in variations in the steam temperature of the outlet. The temperature of the heat exchange fluid flowing through the fluid passages of the heat exchanger, therefore, may be lower in some passages than in others. In most applications where plate heat exchangers are used, the irregularity caused by partial vaporization during the expansion process results in an irregular refrigerant feed, and consequently, an irregular operation between the passages of the system. This means that some parts of the heat exchanger carry more of the load than others, in order to achieve a given operation of the heat exchanger, and maximum operation can be reduced. Because the heat exchange fluid commonly used is water, the passages between some plates also have a tendency to freeze, if these plates are subjected to a greater percentage of liquid refrigerant than others. This can lead to some of the heat exchange fluid circuits freezing, while others continue to flow, thus aggravating the difficulty, and possibly leading to heat exchanger failure. Accordingly, it is desirable to eliminate the difficulties referred to above, to regulate the flow of refrigerant through the passages between the plates of the plate heat exchangers. It is also desirable to provide a uniform distribution of the liquid refrigerant through the refrigerant passages of a plate heat exchange system. It is also desirable to provide a relatively simple and inexpensive distribution of the liquid refrigerant.

BRIEF STATEMENT OF THE INVENTION In accordance with one aspect of the present invention, a plate heat exchanger is provided which includes an assembly of a plurality of plates that separate and define refrigerant elements for the flow of refrigerant and a heat exchange fluid, an element of coolant inlet communicating with the refrigerant passage element; a heat exchange fluid inlet element communicating with the heat exchange fluid passage element; a respective outlet element for the refrigerant and the heat exchange fluid; a coolant distribution element associated with the coolant inlet element, and including a flow control element for regulating and directing the coolant to the respective coolant passage element. In one form of the present invention, the coolant distribution element can include a tube located in the coolant inlet element, the tube having a plurality of holes that create a row of coated holes to direct the coolant to the coolant passages respective. The sizes of the individual orifices can be varied to take into account the pressure loss of the refrigerant along the tube. The holes may also be of variable size to vary the capacity of the heat exchanger in accordance with design considerations or operating parameters. In one embodiment, a tube with holes or holes, or other openings, such as the expansion device, or the pressure reducing device is used, thus obviating the need for an external expansion valve or other pressure reducing element or expansion. With this configuration, the size of the holes or holes can be increased gradually from an inlet end of the tube, thereby providing a uniform distribution of the liquid towards each of the coolant passages. In an alternative embodiment, a tube with holes, holes, or other openings, such as a partial expansion or pressure reduction device, is used in conjunction with an external expansion valve or other expansion or pressure reducing element. With this configuration, partial expansion or pressure reduction occurs externally, and expansion or reduction of final pressure of the liquid refrigerant occurs in the refrigerant distribution element. In still a further embodiment, an auxiliary external expansion valve or other expansion or pressure reducing element is used in conjunction with the refrigerant distribution element. With this configuration, a second coolant distributor is provided in parallel with the first coolant distribution element. The temperature of the refrigerant after expansion through the first refrigerant distribution element is monitored in conjunction with the temperature and / or pressure of the output refrigerant, the inlet and outlet temperatures of the heat exchange fluid, and / or the pressures and the ambient temperature, and the external expansion valve is operated selectively as required to maintain predetermined temperature and / or pressure parameters. In this embodiment, the holes provided in the second manifold are of a relatively large size, to allow the refrigerant at a relatively low pressure to be distributed to the passages. An additional feature of the present invention is the provision of a partial blocking element, to partially close the communication between the refrigerant inlet element and the refrigerant passage element. An opening or hole in the blocking element acts to direct the liquid refrigerant in a predetermined direction, preferably towards the center of the refrigerant passage element, that is, towards the center line of the set of plates. In one form of the present invention, the blocking element can constitute the refrigerant distribution element, while in another form of the present invention, the blocking element is provided to work in conjunction with the refrigerant distribution element. In a preferred embodiment, the blocking element includes a generally C-shaped wire member disposed around the coolant inlet member, between each pair of plates defining the refrigerant passage element. In order that the present invention may be more easily understood, a mode thereof will now be described with reference to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic sectional view of a standard plate heat exchanger showing the path of refrigerant therethrough. Figure 2 is a view similar to that of Figure 1, but showing the heat exchange fluid path. Figure 3 is a view similar to that of Figure 1, illustrating one embodiment of the present invention.

Figure 4 is an enlarged sectional view of the base of the heat exchanger of Figure 3. Figure 5 is a view taken along lines 5-5 of Figure 4. Figure 6 is a schematic perspective view. separated in parts, of the heat exchanger of the Figure 3, but which also shows a modification to the present invention. Figure 7 is a cross-sectional view illustrating the modification of Figure 6. Figure 8 is a view similar to that of Figure 4, but illustrating a further form of the present invention. Figure 9 is a sectional view along lines 9-9 of Figure 8. Figure 10 is a view similar to that of Figure 9, illustrating a still further embodiment of the present invention.

DESCRIPTION OF THE PREFERRED MODALITIES Referring to the drawings, Figures 1 and 2 illustrate a plate heat exchanger 12 which is a set of a plurality of, for example, thirty (30) rib plates 10, the ribs of the adjacent plates intertwining, and adjacent plates defining passages 14 and 16 for refrigerant and heat exchange fluid, respectively. Since water is commonly used as the heat exchange fluid, future reference to this fluid will be made by reference to water. As will be seen more clearly in Figure 5, each plate 10 is formed with two holes 15 at each end, forming the holes 15 of a set of plates 10, inlets and outlets for the coolant and water. The plates 10 separate the coolant passages 14 from the water passages 16, and the plates thus formed, are intermeshed and sealed together, such as by brazing or the like, in such a way that the fluid introduced into one of the lower orifices 15, pass through a series of the coolant and water passages 14 and 16, to exit from a corresponding upper orifice, while fluid is introduced into the other of the lower orifices 15, which will pass through the other series of passages. A coolant inlet manifold 17 communicates with the openings 15, which interconnect the coolant passages 14, and a coolant outlet manifold 18 at the upper end of the heat exchanger, makes it possible for the coolant to exit from the coolant exchanger. hot. Similar multiple water inlet and outlet 19 and 21, respectively, make it possible to circulate water through the water passages 16.

In a standard plate heat exchanger 12, the refrigerant inlet manifold 17 is connected with a supply of high pressure liquid refrigerant 22, through an expansion valve 23, which reduces the refrigerant pressure. As the refrigerant passes through this valve 23, some of the refrigerant evaporates, and mixes with the liquid refrigerant. As a result, a mixture of liquid and gaseous refrigerant enters the heat exchanger 12. Because the mixture is not uniform, and since the gaseous refrigerant occupies a volume substantially larger than the liquid refrigerant, some of the passages of coolant 14 receives more liquid than other passages, such that the amount of liquid and vapor passing through each of the coolant passages 14 varies, thereby causing a variation between the individual coolant passages 14, in the amount of heat transferred between water passages 16 and coolant passages 14. In Figure 1, line 24 illustrates this variation in heat exchange capacity, where there is a phase change between the liquid refrigerant and the vapor. Line 24 is the line of the "phase change termination", and the graph indicates the temperature of the refrigerant leaving the different passages of refrigerant 14. These temperatures can vary from 2 ° C to 11 ° c, depending on the proportion of vapor in the refrigerant entering the individual refrigerant passages 14. The variation in the temperature of the refrigerant vapor leaving the passages 14 results in a similar variation in the temperature of the water leaving the water passages. As shown in Figure 2, the temperature of the water leaving the water passages 16 may vary between 2 ° C and 10 ° C. If the temperature of the water in any of the water passages 16 becomes so low as to cause the water to freeze, additional loads are placed on other parts of the heat exchanger, and the efficiency of the heat exchanger dramatically decreases. This freezing can also lead to a failure of the heat exchanger. Referring to Figures 3 to 7, in one form of the present invention, high pressure liquid refrigerant is delivered directly to a distribution pipe 26 mounted on a coolant inlet manifold 27, and extending through the holes of the plate 15, which communicate with the coolant passages 14. The distribution pipe 26 has a number of small holes or holes 27 which correspond in number a, and are carefully aligned with, the coolant passages 14. The holes orifices 27 can be of different sizes, growing progressively from the manifold 17 to the rear of the heat exchanger 12, in such a way that a uniform distribution of the liquid refrigerant is achieved towards each of the coolant passages 14, independently of the pressure drop along the tube 26. The holes or holes 27 provide the required pressure reduction, and the expansion accompanies The high pressure liquid refrigerant is directly directed to the passages 14, so that there is a uniform distribution of the liquid refrigerant through the entire length of the heat exchanger 12. If required, an external thermal expansion valve can be used. in conjunction with the distribution pipe 26, to provide a desired drop in coolant pressure. Because the holes in the plate 15 communicating with the coolant passages 14 are located towards one side of each plate, C-shaped sheaves 29 are mounted in the coolant passages 14, to substantially surround the openings of the coolant. respective plate 15, and to block direct access to the passages 14. The opening 25 between the ends of each C-shaped sheave 29, directs the liquid refrigerant down and towards the center of the passages 14, to thereby cause that the liquid refrigerant is dispersed uniformly throughout the width of the passages 14. A raised floor 30 on the plates 16, which defines the passages 14, also assists to guide the refrigerant towards the center of the respective passages 14. The tests have shown that with the distribution tube 26 of the present invention, the termination of the phase change between the liquid and vapor refrigerant is presented in a substantially uniform manner throughout the passages 14, as shown by the termination of the phase change line 28 of Figure 3. This results in a substantially uniform temperature of the refrigerant vapor, and consequently, a correspondingly uniform temperature of the water leaving the the water passages 16. By ensuring a uniform distribution of the liquid and vapor in each of the coolant passages 14, the efficiency of the heat exchanger 12 is substantially improved. Tests have also shown that an additional capacity of 10 is obtained. percent from the same heat exchanger test, using a distribution tube 26 in accordance with the described embodiment of the invention, compared to the normal methods of fluid expansion and distribution. Accordingly, by utilizing the features of the present invention, a reduction in the number of plates in a plate heat exchanger is possible, while allowing the minimum leaving water temperatures in any given circuit to run. very close to the average temperature of the exit water. Naturally, a reduction in the number of plates used in the heat exchanger in any given case results in efficiencies for cost and operating efficiencies. With reference to Figures 6 and 7, the holes 27 of the tube 26 can be varied in size to take into account the different operating parameters in the different refrigerant and air conditioning systems, which give rise to different refrigerant requirements. For this purpose, the tube 26 has a sleeve 26a thereon, which can be rotated in relation to the tube 26, to close or open the holes 27 as desired. The sleeve 26a can be fixed in its position by any suitable element. Referring to Figures 8 and 9, a modified form of the present invention is illustrated, wherein a second liquid coolant distribution pipe 31 extends through the holes of the plate 15, which communicates with the coolant passages. 14 substantially parallel to the first liquid refrigerant distribution tube 26. The second tube 31 is provided with holes that correspond in number, and are substantially aligned with the holes or holes 27 of the distribution tube 26, the orifices 32 being of substantially a size larger than the holes or holes 27. The second refrigerant pipe 31 is connected, externally to the heat exchanger 12, with the high pressure liquid refrigerant line 33, through an expansion valve 34 The second liquid refrigerant pipe 31 provides additional refrigerant capacity for exchanger 12, as may be required during the start-up that and during the operation in conditions of low ambient temperature, particularly using air-cooled condensers in the refrigerant circuit. The input manifold 17 also carries a temperature sensing probe 36, and other sensors (not shown) are used to determine the temperature and / or pressure at the refrigerant outlet, as well as the water inlet and outlet temperatures, for regulating the operation of the expansion valve 34. In this way, the provision of the second liquid refrigerant tube 31 improves the operational capacity of the heat exchanger 12 during a scale of operating conditions, thereby increasing the efficiency of the system in which it operates. The heat exchanger is installed. As will be seen in Figures 8 and 9, the C-shaped sheaves 29 are also used in this embodiment, and both series of holes 27 and 32 are directed towards the opening 25 between the ends of the sheave. The orientation of the orifices in relation to the orientation of the tubes is configured to ensure that the orifices 32 are directed away from the tube 26. Referring to Figure 6, a further embodiment of the present invention is illustrated, wherein the distribution of the The refrigerant is carried out by means of a thinned tube 37 which extends through the holes of the plate 15, which communicate with the passages of the refrigerant 14. The tube 37 is similar to the tube 26 of the embodiments illustrated in Figures 3 to 7, except that its cross-sectional area decreases from the end of the multiple coolant to the opposite end of the tube 37. The holes 38 of the thinned tube 37, corresponding to the holes 27 of the tube 26, are each of an identical size., and it is the thinning of the tube that ensures a uniform distribution of the liquid refrigerant through the orifices 38. Although the refrigerant passages 14 can be partially blocked using the C-shaped rings or rollers 29 as shown in the above embodiments , an alternative lock is illustrated in Figure 10, which includes a lock tube having a slot 41 along one side. The blocking tube 39 is inserted through the holes of the plate 15 (the orifices communicating the coolant passages 14), so that the groove 41 generally faces inwards and downwards, similar to the location of the opening between the ends of the C-shaped rollers 29 of the above embodiments. The blocking tube can be formed of a material that can be welded to the plates 16 around the holes 15, in which case, the blocking tube 39 is inserted before the final welding step in the construction of the heat exchanger 12. Alternatively, the locking tube 39 can be inserted after the final welding step, in which case, the blocking tube can be formed of any suitable material, including plastic. If the material of the blocking tube is a resilient material, the tube 39 can be formed with an outer diameter larger than the diameter of the holes of the plate 15, whereby the insertion is effected by compressing the tube in such a way that the slot 41 along one side is closed, thereby reducing the diameter of the tube enough to make it possible to insert through the holes in the plate 15. If desired, circumferential grooves can be formed in the tube of blocking 39, such that, when properly located in place, the edges of the holes in the plate 15 settle into the circumferential grooves. Sealing or adhesive materials may be used, if desired, to locate and seal the locking tube 39 in its desired position. It will be understood that the modifications of the present invention may include other elements to choke the flow of liquid refrigerant from the refrigerant inlet manifold 17 to the individual passages 14. Since this drowning is variable to uniformize the flow of liquid refrigerant and vapor towards each passage 14, efficiencies similar to those of the particular embodiments described above could be expected. It will be appreciated that the present invention also allows for the removal of the normal expansion valve or other types of refrigerant or expansion pressure reducing devices, thereby allowing for reduced manufacturing costs, while there is a marked increase in the operation of the heat exchanger.

Claims (26)

1. CLAIMS 1. A plate heat exchanger including a set of a plurality separating and defining passage elements for the flow of refrigerant and a heat exchange fluid; a refrigerant inlet element communicating with the refrigerant passage elements; a heat exchange fluid inlet element communicating with the heat exchange fluid passage elements; a respective outlet element for the refrigerant and the heat exchange fluid; a coolant distribution element associated with the coolant inlet element, and including a flow control element for regulating and directing the coolant to the respective coolant passage elements.
2. 2. A plate heat exchanger according to claim 1, characterized in that the coolant inlet element includes aligned holes in the plates, and the distribution element includes a tube located in the coolant inlet element, the tube having a plurality of openings which form the flow control element, and from which the refrigerant is directed towards each of the refueling passage elements.
3. 3. A plate heat exchanger according to claim 2, characterized in that the plurality of openings vary in size from one end of the tube to the other.
4. 4. A plate heat exchanger according to claim 2, characterized in that the adjustment element is provided to selectively change the cross-sectional area of the openings, thereby changing the flow of refrigerant through the the same.
5. 5. A plate heat exchanger according to claim 2, characterized in that the tube and the plurality of openings are of a size to constitute a refrigerant pressure reducing device, which reduces the pressure of the liquid refrigerant supplied to the tube, up to a previously determined relatively low pressure.
6. 6. A plate heat exchanger according to claim 2, characterized in that the tube is thinned from a larger cross-sectional area at one coolant inlet end, to a smaller cross-sectional area at the remote end of the input end.
7. 7. A plate heat exchanger according to claim 1, characterized in that the partial blocking element is provided in each refrigerant passage element, to partially surround the refrigerant inlet element, or in the refrigerant inlet element, the partial blocking element confining the flow of refrigerant from the distribution element along a predetermined path defined by an opening in the partial blocking element.
8. 8. A plate heat exchanger according to claim 7, characterized in that the opening is located to direct the flow of refrigerant to a central line of the respective refrigerant passage element,
9. 9. A plate heat exchanger according to claim 7, or claim 8, characterized in that the flow control element directs coolant from the distribution element towards the opening.
10. 10. A plate heat exchanger according to claim 7, characterized in that the partial blocking element includes a plurality of C-shaped members sealed to the plates, which define each of the elements of refrigerant passage, and surrounding the holes of the plates, whose holes define the coolant inlet element.
11. 11. A plate heat exchanger according to claim as claimed in any of claims 7 to 9, characterized in that the partial blocking element includes a tube-like member having a groove along one side, the member being located in the coolant inlet element defined by holes aligned in the plates, the groove of the tube forming the opening.
12. 12. A plate heat exchanger as claimed in any of the preceding claims, characterized in that the second refrigerant distribution element is arranged in the refrigerant inlet element, the second refrigerant distribution element being connected with a supply of high pressure liquid refrigerant through a selectively operated pressure reducing valve.
13. 13. A plate heat exchanger according to claim 12, characterized in that the second refrigerant distribution element includes a tube having a plurality of relatively large orifices to direct refrigerant to each of the passage elements. of refrigerant.
14. 14. A plate heat exchanger that includes a set of plates that separate and define alternating passages for the flow of a refrigerant and a heat exchange fluid, forming each of the plates with holes that, in the set, define a an inlet element and an outlet element by which the refrigerant and the heat exchange fluid are caused to flow through the respective passages, a refrigerant distribution tube extending from one side of the assembly through the cooling element. refrigerant inlet, this distribution tube being closed at its remote end of the first side of the assembly, and having a plurality of openings, each aligned with, and directed towards, one of the passages of the refrigerant, to direct the refrigerant supplied to the tube , towards these passages.
15. 15. A plate heat exchanger according to claim 14, characterized in that the distribution tube is connected to a high pressure liquid refrigerant line, by which the refrigerant is supplied to the tube under a relatively high pressure. high, and the tube and openings constitute a pressure reducing element, by which, the pressure of the refrigerant is reduced as it enters the refrigerant passages.
16. 16. A plate heat exchanger according to claim 15, characterized in that the auxiliary refrigerant distributor extends through the coolant inlet element, substantially parallel with the tube.
17. 17. A plate heat exchanger according to claim 16, characterized in that the auxiliary distributor tube is connected to the high pressure liquid refrigerant line through a pressure reducing device, in such a way that the pressure of the refrigerant in the auxiliary distributor tube is relatively low, the auxiliary distributor tube having relatively large orifices through which the refrigerant is distributed at a relatively low pressure towards the refrigerant passages.
18. 18. A plate heat exchanger according to claim 17, characterized in that the pressure reducing device is selectively operated in accordance with the load on the heat exchanger, as determined by the inlet and outlet temperatures. of the refrigerant and the heat exchange fluid.
19. 19. A plate heat exchanger as claimed in any of claims 14 to 18, characterized in that the openings in the distribution tube increase in size from the first side to the remote end.
20. 20. A plate heat exchanger as claimed in any of claims 14 to 19, characterized in that the cross-sectional areas of the openings are variable.
21. 21. A plate heat exchanger according to claim 17, characterized in that a sleeve is engaged on the distribution tube, the sleeve having one or more openings aligned with the openings, and being able to move selectively to vary the size of the openings.
22. 22. A plate heat exchanger as claimed in any of claims 14 to 21, characterized in that a blocking element is provided in the refrigerant inlet element, or in each refrigerant passage, to confine the flow of the refrigerant. coolant from the input element to a predetermined path defined by an opening in the blocking element.
23. 23. A plate heat exchanger according to claim 22, characterized in that the blocking element includes C-shaped wire members, sealed in the passages, and extending around the entry element.
24. 24. A plate heat exchanger according to claim 22, characterized in that the blocking element includes a substantially C-shaped tube-shaped member positioned on the input element.
25. 25. A plate heat exchanger as claimed in any of claims 14 to 24, characterized in that the distributor tube has a cross-sectional area that decreases from the first side of the assembly to the remote end.
26. 26. A plate heat exchanger, substantially as described hereinabove, with reference to the accompanying drawings.