HEAT EXCHANGER

Abstract

An evaporator with a plurality of tubes which extend through the shell. The plurality of tubes have first respective tubes and second respective tubes, the second respective tubes being proximate to and laterally displaced from the first respective tubes. A generally vertical partition is positioned to direct the flow of the process fluid through the plurality of tubes in a generally sideways pattern.

Description

BACKGROUND

The application is directed to shell and tube heat exchangers. The application relates more particularly to a flooded evaporator having a tube arrangement that permits reduced refrigerant levels to be used.

Shell and tube flooded evaporators may be used in vapor compression systems. In a typical vapor compression system, there is an evaporator that cools a process fluid at the expense of boiling a liquid; a compressor that compresses the boiled off liquid, i.e., a vapor, to an elevated pressure and temperature; a condenser that condenses the compressed vapor to liquid phase; and an expansion device that lowers the pressure of the condensed liquid which then enters the evaporator to repeat the above cycle.

In a flooded evaporator, the process fluid is dispersed into and through numerous tubes that pass through a tank, or shell, containing the liquid refrigerant. The process fluid is cooled while some of the liquid is boiled away as described above. Depending on the level of cooling to be achieved, the process fluid may make multiple passes through the liquid.

Flooded evaporators may use several different quantities of tubes with the same shell diameter to obtain commonality in manufacturing. However, current multi-pass flooded evaporators are arranged so that process fluid passes through groups of tubes in a vertically upward, bottom-to-top fashion through the shell. As a result, regardless of the number of tubes used within a particular shell of a multi-pass flooded evaporator, the shell needs to be filled with the maximum or near-maximum level of liquid to ensure that all of the tubes remain immersed within the liquid to accomplish the desired heat transfer.

SUMMARY

The present invention relates to a heat exchanger having a shell with a first process fluid box at one end and a second process fluid box at an opposed end. A plurality of tubes are disposed in the shell and extend from the first process fluid box to the second process fluid box. The plurality of tubes has a first set of tubes and a second set of tubes; the second set of tubes are laterally displaced from the first set of tubes. The first process fluid box and the second process fluid box are configured to direct a process fluid through the first set of tubes in a first direction and to direct the process fluid through the second set of tubes in a second direction opposite the first direction.

In one exemplary embodiment, the first process fluid box has an inlet nozzle configured to receive the process fluid, an outlet nozzle configured to discharge the process fluid, and a partition positioned between the inlet nozzle and the outlet nozzle. The partition is configured to direct the process fluid from the inlet nozzle into the first set of tubes and to direct the process fluid from the second set of tubes into the outlet nozzle.

In another exemplary embodiment, the first process fluid box comprises a first partition and an inlet nozzle configured to receive the process fluid, the partition is configured to direct the process fluid from the inlet nozzle into the first set of tubes and to direct the process fluid from the second set of tubes into a third set of tubes of the plurality of tubes, the third set of tubes being laterally displaced from the second set of tubes. The second process fluid box has a second partition and an outlet nozzle configured to discharge the process fluid, the second partition is configured to direct the process fluid from the first set of tubes into the second set of tubes and to direct the process fluid from the third set of tubes to the outlet nozzle.

The present invention further relates to an evaporator having a shell with a first header at one end and a second header at an opposed end. A plurality of tubes are disposed in the shell and extend from the first header to the second header. The plurality of tubes has a first set of tubes and a second set of tubes; the second set of tubes are laterally displaced from the first set of tubes. A first partition is positioned in the first header, the first partition has a generally vertical orientation to direct flow of the process fluid through the plurality of tubes in a generally lateral direction.

According to exemplary embodiments, by rearranging the fluid boxes so that process fluid passes in a sideways manner through the tubes in the shell, the tubes in the shell can be used from the bottom up. As a result, when fewer tubes are used, the level of refrigerant required in the shell can likewise be reduced. A reduction in the level of refrigerant may result in substantial cost savings to the end user, who can purchase less refrigerant, which is often very expensive. Further, environmental benefits associated with lower refrigerant usage may be obtained. Thus, exemplary embodiments of the application may arrange the tubes, and the partitions, which direct process fluid into the tubes, in a way that permits the refrigerant level to be varied based on the number of tubes actually used in a particular flooded evaporator.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an exemplary environment for a chilled liquid system.

FIG. 2 shows an isometric view of an exemplary vapor compression system that is part of a chilled liquid system.

FIG. 3 schematically shows an exemplary embodiment of a vapor compression system.

FIG. 4 shows an exemplary embodiment of a two-pass evaporator.

FIG. 5 shows an exemplary embodiment of a three-pass evaporator.

FIG. 6 shows a cross-sectional view of an exemplary embodiment of a two-pass evaporator taken along line 6-6 of FIG. 7.

FIG. 7 shows an end view of an exemplary embodiment of a process fluid box for a two-pass evaporator.

FIG. 8 shows an exemplary embodiment of tube supports positioned on an evaporator inlet distributor.

FIG. 9 shows an exemplary embodiment of a tube support with four alternative tube arrangements for use in either a two-pass or three-pass evaporator.

FIG. 10 shows a cross-sectional end view of an exemplary embodiment of an evaporator.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows an exemplary embodiment for a chilled liquid system 10 in a building 12 for a typical commercial setting. System 10 can include a vapor compression system 14 that can supply a chilled liquid that may be used to cool building 12. System 10 can also include a boiler 16 to supply a heated liquid that may be used to heat building 12, and an air distribution system that circulates air through building 12. The air distribution system can include an air return duct 18, an air supply duct 20 and an air handler 22. Air handler 22 can include a heat exchanger that is connected to boiler 16 and vapor compression system 14 by conduits 24. The heat exchanger in air handler 22 may receive either heated liquid from boiler 16 or chilled liquid from vapor compression system 14 depending on the mode of operation of system 10. System 10 is shown with a separate air handler on each floor of building 12, but it will be appreciated that the components may be shared between or among floors.

FIGS. 2 and 3 show an exemplary vapor compression system 14 that can be used in chilled liquid system 10. Vapor compression system 14 can circulate a refrigerant through a compressor 32 driven by a motor 50, a condenser 34, expansion device(s) 36, and a liquid chiller or evaporator 38. Vapor compression system 14 can also include a control panel 40 that can include an analog to digital (A/D) converter 42, a microprocessor 44, a non-volatile memory 46, and an interface board 48. Some examples of fluids that may be used as refrigerants in vapor compression system 14 are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407, R-134a, or any other suitable type of refrigerant.

Motor 50 used with compressor 32 can be powered by a variable speed drive (VSD) 52 or can be powered directly from an alternating current (AC) or direct current (DC) power source. VSD 52, if used, receives AC power having a particular fixed line voltage and fixed line frequency from the AC power source and provides power having a variable voltage and frequency to motor 50. Motor 50 can be any type of electric motor that can be powered by a VSD 52 or directly from an AC or DC power source. For example, motor 50 can be a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor or any other suitable motor type. In an alternate exemplary embodiment, other drive mechanisms such as steam or gas turbines or engines and associated components can be used to drive compressor 32.

Compressor 32 compresses a refrigerant vapor and delivers the vapor to condenser 34 through a discharge line. Compressor 32 can be a centrifugal compressor, screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, turbine compressor, or any other suitable compressor. The refrigerant vapor delivered by compressor 32 to condenser 34 transfers heat to a fluid, e.g., water or air. The refrigerant vapor condenses to a refrigerant liquid in condenser 34 as a result of the heat transfer with the fluid. The liquid refrigerant from condenser 34 flows through expansion devise 36 to evaporator 38. In the exemplary embodiment shown in FIG. 3, condenser 34 includes a tube bundle 54 connected to a cooling tower 56.

The liquid refrigerant delivered to evaporator 38 absorbs heat from another fluid, which may or may not be the same type of fluid used for condenser 34, and undergoes a phase change to a refrigerant vapor. In the exemplary embodiment shown in FIG. 3, evaporator 38 includes a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. A process fluid-for example, water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable liquid-enters evaporator 38 via return line 60R and exits evaporator 38 via supply line 60S. Evaporator 38 chills the temperature of the liquid in the tubes. Tube bundle 58 can include a plurality of tubes and a plurality of bundles. The vapor refrigerant exits evaporator 38 and returns to compressor 32 by a suction line to complete the cycle.

FIGS. 4 and 5 show exemplary embodiments of evaporator 38. Evaporator 38 includes a shell 62 containing refrigerant 64 (see FIG. 6), an inlet 24 to receive liquid refrigerant 64 from condenser 34, and an outlet 26 from which vapor refrigerant is pulled to compressor 32. Compressor 32 may be mounted on top of evaporator 38. Evaporator 38 also has process fluid boxes 68, 70 or headers on each end to enclose an end of shell 62 and serve as a distributor or manifold for the process fluid to enter or exit tubes 72 (see FIG. 6) positioned in shell 62. Tubes 72 of evaporator 38 extend from process fluid box 68 on one end of shell 62 to the process fluid box 70 at the opposite end of shell 62. Process fluid boxes 68, 70 separate the process fluid from refrigerant 64 in shell 62 so that the process fluid in tubes 72 is not mixed with refrigerant 64 during the heat transfer process between the process fluid in tubes 72 and the liquid refrigerant 64 in shell 62.

FIG. 4 shows evaporator 38 in a two-pass configuration, i.e., process fluid enters through an inlet nozzle 76 and into process fluid box 68 of a first end of the evaporator 38, passes through a first set of tubes 72 to process fluid box 70 at the other end of evaporator 38, where the process fluid changes direction and then makes a second pass back through shell 62 in a second set of tubes 72. The process fluid then exits the evaporator 38 through an outlet nozzle 78 on the same end of evaporator 38 as the inlet nozzle 76. FIG. 5 shows evaporator 38 in a three-pass configuration where, instead of exiting outlet nozzle 78 from process fluid box 68 on the same end as inlet nozzle 76, the process fluid changes direction and passes back through shell 62 (and thus into a heat exchange relationship with refrigerant 64) in a third set of tubes 72, exiting evaporator 38 via outlet nozzle 78 on process fluid box 70 on the opposite end of evaporator 38 from inlet nozzle 76.

Different partitions or baffles are positioned within process fluid boxes 68, 70 depending on whether a two-pass or three-pass evaporator is used. FIG. 7 shows process fluid box 68 for a two-pass evaporator 38 having a partition 41 to divide the passes in process fluid box 68. A three-pass evaporator 38 can have two partitions, each positioned in a respective process fluid box 68, 70. The partitions direct the process fluid through tubes 72 in the desired pattern and also prevent the mixing of process fluids from different passes.

FIG. 6 shows a cross sectional side view of a two-pass evaporator 38 including tube supports 84, with all but the bottom row of tubes 72 removed for clarity. FIG. 10 shows a cross-sectional end view of a two- or three-pass evaporator, again with tubes removed for clarity. The particular configuration of evaporator 38 is dependent on the configuration of partitions and partitions in process fluid boxes 68, 70.

FIG. 7 shows a front view of process fluid box 68 from the nozzle end of a two-pass evaporator 38. Partition 41 separates the entering, uncooled process fluid in process fluid box 68 from the exiting process fluid that has passed twice through refrigerant 64 in the shell 62. Partition 41 is oriented in a vertical manner to produce a generally sideways flow of process fluid through the evaporator 38, unlike current flooded evaporators in which the partitions are arranged substantially horizontally to produce an upwardly cascading flow of process fluid through the evaporator.

While exemplary embodiments include partitions which are generally vertical, due to the circular cross section of evaporator 38 and to allow adequate room for the inlet and outlet nozzles 76, 78, the partition(s) may be slightly angled to permit a more even distribution of tubes 72 on each side of the partition(s).

FIG. 8 shows in more detail tube supports 84 which are positioned within shell 62 of evaporator 38 as shown in FIG. 6. Two or more tube supports 84 are positioned within evaporator 38. Tube supports 84 have multiple apertures 86 to receive tubes 72. Tube supports 84 (and their respective apertures 86) are aligned such that during evaporator assembly, tubes 72 can be inserted through, and supported within shell 62 by, tube supports 84. Tube supports 44 may be aligned within shell 62 to straddle a refrigerant inlet distributor 88. Additionally, one or more support ribs 90 may be positioned over the tube supports 84 to provide additional stability during and/or after assembly.

Regions 92 of tube supports 84 without apertures may be provided to correspond to the partitions' position in process fluid boxes 68, 70 so that tubes 72 are not inadvertently inserted into evaporator 38 during manufacture that would conflict with the partitions when the process fluid boxes 68, 70 are mounted on shell 62.

FIG. 9 shows a plan view of tube support 84 for use in either a two-pass or a three-pass arrangement of evaporator 38 and illustrates by regions 92 where the partitions would be positioned within the process fluid boxes 68, 70 with respect to tube support 84 depending on whether a two-pass configuration (one partition) or a three-pass configuration (two partitions) was being employed. For example, in a three-pass arrangement of evaporator 38, process fluid would flow from process fluid box 68 on the inlet nozzle end of evaporator 38 and into a first group of tubes 100 to the process fluid box 70 at the opposite end (i.e., outlet nozzle end) of evaporator 38. From process fluid box 70, the fluid would then flow through a second and third group of tubes 102, 104 back to process fluid box 68 and then back through a fourth group of tubes 106 to process fluid box 70 (and out of the evaporator). A partition or partition may be positioned in process fluid box 68 between tube group 100 and tube group 102 and another partition or partition may be positioned in process fluid box 70 between tube group 104 and tube group 106 to achieve a sideways or lateral flow pattern for the process fluid passes. A sideways flowpath in a two-pass evaporator is accomplished by a single partition 41 in process fluid box 68 between tube group 102 and tube group 104. Any greater number of odd or even passes may be employed, provided an appropriate number of partitions are employed to achieve the side-to-side flow pattern.

Tube support 84 can be used in any one of four different tube configurations for each of either a two- or three-pass evaporator arrangement. It will be appreciated, however, that other tube configurations may be used depending on the capacity to be achieved.

In a first configuration of tube support 84, as shown in FIG. 5, tubes for carrying process fluid are inserted through all of tube support apertures 86 identified as “1” while the remaining apertures are unused. In a second configuration of tube support 84, tubes for carrying process fluid are inserted through all of tube support apertures 86 identified as “2” in addition to all of apertures identified as “1”. In a third configuration, tubes pass through all of the apertures identified as “1”, “2” and “3”; and likewise for the fourth configuration, further adding tubes to apertures as “4.”

In each of the different tube support configurations, the sideways flow of process fluid allows the shell 62 to be filled with tubes 72 from refrigerant inlet distributor 88 toward outlet 26, meaning that the height of the top row of tubes 72 varies with the total number of tubes 72 in evaporator 38. As a result, when evaporator 38 is in a “1” configuration of tube support 84, shell 62 only needs to be filled with refrigerant 64 to a level slightly higher than the top row of tubes identified as “1” and not all the way to the top of tube supports 84. Put another way, in exemplary embodiments, the unused tube support apertures 86 are above the top row of tubes 72, while in evaporators using an upwardly cascading flow, the unused tube support apertures are distributed throughout the tube support, requiring the refrigerant to be filled higher to reach the top row of tubes in that cascading arrangement. Furthermore, it has been determined that even with the maximum equivalent tube count, the sideways flow arrangement for the process fluid still achieves a lower overall tube height and corresponding refrigerant level than in the cascading arrangement.

In an exemplary embodiment, as shown in FIG. 9, the tube support apertures 86 are arranged in tube support 84 such that the same tube supports 84 can be used in either a two-pass or a three-pass evaporator. In either embodiment, tube support apertures 86 are such that the number of tubes 72 in the top row for each tube support configuration is approximately the same (for example, within about 5 of one another) while also keeping the total number of tubes for each pass within about 5. For example, as shown in FIG. 9 with respect to the “3” configuration, tubes 72 would be arranged such that the top row of tubes has eight tubes for each of the three passes in a three-pass evaporator or twelve tubes for each pass if used in a two-pass evaporator. Similarly, for a “1” configuration, the top row has a 15/11 tube count split for a two-pass evaporator or an 11/8/7 split for a three-pass evaporator.

It has been determined that balancing the number of tubes 72 between passes as much as possible results in better performance by reducing the total height of the tube stack, and thus the total volume of refrigerant 64 needed to cover the stack. Thus, tube support apertures 86 and process fluid partitions can be positioned so that for each incremental increase in tube quantity in the evaporator, there is no more than 1 row of difference in the height of the top tube in each section (group or pass) when filled from the bottom up. While not required, the incremental tube quantities may be selected to perfectly fill the top row, because any empty tube space in a row must be filled by additional refrigerant.

Because of the reduced overall height of the tube stack achieved with exemplary embodiments, it may be desirable to include a tube head support rib 94 (FIGS. 2 and 6) to provide structural support to the shell 62. Under some ASME standards, shell 62 must meet a certain overall strength. Decreasing the height of the tube stack may cause a decrease in that strength, which can be compensated for by the use of tube head support rib 94.

An exemplary embodiment of evaporator having the sideways flow arrangement in the “1” tube support configuration, the amount of refrigerant required in a system with evaporator 38 was reduced by 24% compared to that required for a system with an evaporator having the same number of tubes but arranged in an upward bottom-to-top flow pattern of process fluid. Further, the amount of refrigerant in the evaporator itself is even more significantly reduced. Even when the evaporator uses the maximum amount of tubes (i.e., the “4” tube support configuration), the sideways flow pattern of exemplary embodiments results in an overall reduction in the height of the tube stack compared to a cascading flow pattern.

While only certain features and embodiments of the invention have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or resequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.

Claims

1. An heat exchanger comprising:

a shell comprising a first process fluid box at one end of the shell and a second process fluid box at an opposed end of the shell;

a plurality of tubes disposed in the shell, the plurality of tubes extending from the first process fluid box to the second process fluid box, the plurality of tubes comprising a first set of tubes and a second set of tubes, the second set of tubes being laterally displaced from the first set of tubes;

the first process fluid box and the second process fluid box being configured to direct a process fluid through the first set of tubes in a first direction and to direct the process fluid through the second set of tubes in a second direction opposite the first direction.

2. The heat exchanger as recited in claim 1 wherein the first process fluid box comprises an inlet nozzle configured to receive the process fluid, an outlet nozzle configured to discharge the process fluid, and a partition positioned between the inlet nozzle and the outlet nozzle, the partition being configured to direct the process fluid from the inlet nozzle into the first set of tubes and to direct the process fluid from the second set of tubes into the outlet nozzle.

3. The heat exchanger as recited in claim 1 wherein the first process fluid box comprises a first partition and an inlet nozzle configured to receive the process fluid, the partition being configured to direct the process fluid from the inlet nozzle into the first set of tubes and to direct the process fluid from the second set of tubes into a third set of tubes of the plurality of tubes, the third set of tubes being laterally displaced from the second set of tubes.

4. The heat exchanger as recited in claim 3 wherein the second process fluid box comprises a second partition and an outlet nozzle configured to discharge the process fluid, the second partition being configured to direct the process fluid from the first set of tubes into the second set of tubes and to direct the process fluid from the third set of tubes to the outlet nozzle.

5. The heat exchanger as recited in claim 4 wherein the partition and the second partition are angled to divide the plurality of tubes substantially equally between the first set of tubes, the second set of tubes and the third set of tubes.

6. The heat exchanger as recited in claim 2 wherein the partition has a generally vertical orientation to facilitate a lateral flow of the process fluid through the plurality of tubes.

7. The heat exchanger as recited in claim 2 further comprising a tube support in the shell, the tube support comprising a plurality of apertures and configured to receive and support the plurality of tubes extending through the shell.

8. The heat exchanger as recited in claim 7 wherein the tube support comprises a region without apertures, the region corresponding to the position of the partition.

9. The heat exchanger as recited in claim 7 further comprising a rib positioned in the shell above the tube support, the rib being configured to provide additional support and stability to the shell.

10. The heat exchanger as recited in claim 1 wherein the shell comprises an inlet configured to receive refrigerant, the first set of tubes extending from the inlet to a first height, and the second set of tubes extending from the inlet to a second height substantially equal to the first height.

11. An evaporator comprising:

a shell having a header at one end of the shell and a second header at an opposed end of the shell;

a plurality of tubes disposed in the shell, the plurality of tubes extending from the first header to the second header, the plurality of tubes comprising a first set of tubes and second set of tubes, the second set of tubes being laterally displaced from the first set of tubes;

a first partition positioned in the first header, the first partition having a generally vertical orientation to direct flow of the process fluid through the plurality of tubes in a generally lateral direction.

12. The evaporator as recited in claim 11 wherein the first header comprises an inlet nozzle configured to receive the process fluid, an outlet nozzle configured to discharge the process fluid, and the first partition positioned between the inlet nozzle and the outlet nozzle, the first partition being configured to direct the process fluid from the inlet nozzle into the first set of tubes and to direct the process fluid from the second set of tubes into the outlet nozzle.

13. The evaporator as recited in claim 11 wherein the first header comprises the first partition and an inlet nozzle configured to receive the process fluid, the first partition being configured to direct the process fluid from the inlet nozzle into the first set of tubes and to direct the process fluid from the second set of tubes into a third set of tubes of the plurality of tubes, the third set of tubes being laterally displaced from the second set of tubes.

14. The evaporator as recited in claim 13 wherein the second header comprises a second partition and an outlet nozzle configured to discharge the process fluid, the second partition being configured to direct the process fluid from the first set of tubes into the second set of tubes and to direct the process fluid from the third set of tubes to the outlet nozzle.

15. The evaporator as recited in claim 14 wherein the second partition has a generally vertical orientation to facilitate a lateral flow of the process fluid through the plurality of tubes.

16. The evaporator as recited in claim 11 wherein the shell comprises an inlet configured to receive refrigerant, the first set of tubes extending from the inlet to a first height, and the second set of tubes extending from the inlet to a second height substantially equal to the first height.

17. An heat exchanger comprising:

a shell comprising a first process fluid box at one end of the shell and a second process fluid box at an opposed end of the shell;

a plurality of tubes disposed in the shell, the plurality of tubes extending from the first process fluid box to the second process fluid box, the plurality of tubes comprising a first set of tubes and a second set of tubes;

the first process fluid box and the second process fluid box being configured to direct a process fluid through the first set of tubes in a first direction and to direct the process fluid through the second set of tubes in a second direction opposite the first direction;

a tube support positioned in the shell, the tub supports have apertures to receive the first set of tubes and the second set of tubes.

18. The heat exchanger as recited in claim 17 wherein a support rib is provided proximate the tube support, the support rib providing support to the tube support.

19. The heat exchanger as recited in claim 17 wherein the first process fluid box comprises an inlet nozzle configured to receive the process fluid, an outlet nozzle configured to discharge the process fluid, and a partition positioned between the inlet nozzle and the outlet nozzle, the partition being configured to direct the process fluid from the inlet nozzle into the first set of tubes and to direct the process fluid from the second set of tubes into the outlet nozzle.

20. The heat exchanger as recited in claim 19 where a region is provided on the tube support, the position of the region on the tube support corresponds to the position of the partition in the first process fluid box.