WO2019071415A1

WO2019071415A1 - Systems and methods for falling film evaporator tubesheets

Info

Publication number: WO2019071415A1
Application number: PCT/CN2017/105484
Authority: WO
Inventors: Fang XUE; Xiuping Su
Original assignee: York (Wuxi) Air Conditioning And Refrigeration Co., Ltd.; Johnson Controls Technology Company
Priority date: 2017-10-10
Filing date: 2017-10-10
Publication date: 2019-04-18
Also published as: CN111316053B; CN111316053A

Abstract

A heating, ventilating, air conditioning, and refrigeration (HVAC&R) system (10) includes a falling film evaporator (38) configured to vaporize a low pressure refrigerant liquid into a low pressure refrigerant gas. The falling film evaporator (38) includes a shell (106), a lower tube bundle (102) and a upper tube bundle (104). The shell (106) includes a first tubesheet (240) disposed at a first end portion of the shell (106) and a second tubesheet (242) disposed at a second end portion of the shell (106). The lower tube bundle (102) is disposed within a bottom portion of the shell (106), and the upper tube bundle (104) is disposed above the lower tube bundle (102), each of the lower tube bundle (102) and the upper tube bundle (104) has ends respectively supported by the first and the second tubesheets (240, 242). An upper edge (136) of the upper tube bundle (104) extends above a horizontal midline of the shell (106) to enable the upper tube bundle (104) and the lower tube bundle (102) to distribute a force across a vertical extent of the first tubesheet (240) and the second tubesheet (242).

Description

SYSTEMS AND METHODS FOR FALLING FILM EVAPORATOR TUBESHEETS

BACKGROUND

The present disclosure relates generally to heating, ventilating, air conditioning, and refrigeration (HVAC&R) systems, and more particularly to systems and methods for falling film evaporator construction and tube arrangement in HVAC&R systems.

Vapor compression systems utilize a working fluid, typically referred to as a refrigerant, which changes phases between vapor, liquid, and combinations thereof in response to being subjected to different temperatures and pressures associated with operation of the vapor compression system. Certain vapor compression systems include an evaporator having a certain tube arrangement with a tube bundle disposed in a lower portion of a shell of the evaporator. For example, a flooded evaporator may include the certain tube arrangement to enable fluid flowing through tubes of the tube bundle to exchange thermal energy with a pool of refrigerant. Unfortunately, the certain tube arrangement may focus stress onto a small portion of typical supporting elements of the flooded evaporator, such as tubesheets, and use larger supporting elements. Thus, the flooded evaporator having the certain tube arrangement uses more materials and involves a longer installation time to install and operate.

SUMMARY

In one embodiment of the present disclosure, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a falling film evaporator configured to vaporize a low pressure refrigerant liquid into a low pressure refrigerant gas. The falling film evaporator includes a shell including a first tubesheet disposed at a first end portion of the shell and a second tubesheet disposed at a second end portion of the shell. The falling film evaporator also includes a lower tube bundle disposed within a bottom portion of the shell and having a first lower bundle end and a second lower bundle end respectively supported by the first tubesheet and the second tubesheet. Further, the falling film evaporator includes an upper tube bundle disposed above the lower tube bundle within the shell and having a first upper bundle end and a second upper bundle end respectively supported by the first tubesheet and the second tubesheet. Moreover, an upper edge of the upper tube bundle extends above a horizontal midline of the shell to enable the upper tube bundle and the lower tube bundle to distribute a force across a vertical extent of the first tubesheet and the second tubesheet.

In another embodiment of the present disclosure, a method of designing a falling film evaporator includes determining, via a processor of a computing device, a tubesheet stress on a tubesheet of the falling film evaporator. The tubesheet is configured to support an end of a lower tube bundle and an upper tube bundle disposed within a shell. Additionally, the upper tube bundle extends above a horizontal midline of the shell. The method also includes calculating, via the processor, a thickness of the tubesheet based on the tubesheet stress.

Other features and advantages of the present application will be apparent from the following, more detailed description of the embodiments, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the application.

DRAWINGS

FIG. 1 is a perspective view of an embodiment of a building that may utilize a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system in a commercial setting, in accordance with the present techniques；

FIG. 2 is a perspective view of an embodiment of a vapor compression system, in accordance with the present techniques；

FIG. 3 is a schematic diagram of an embodiment of the vapor compression system, in accordance with the present techniques；

FIG. 4 is a schematic diagram of an embodiment of the vapor compression system, in accordance with the present techniques；

FIG. 5 is a cross-sectional view of an embodiment of an evaporator of the vapor compression system having a tube arrangement for reducing or minimizing a tubesheet thickness, in accordance with the present techniques；

FIG. 6 is a side schematic view of an embodiment of the evaporator having the tube arrangement, in accordance with the present techniques；

FIG. 7 is a schematic diagram of an embodiment of a Finite Element Analysis (FEA) screen overlay for a modeled tubesheet of the vapor compression system, in accordance with the present techniques； and

FIG. 8 is another schematic diagram of an embodiment of a FEA screen overlay for the modeled tubesheet, in accordance with the present techniques.

DETAILED DESCRIPTION

The present disclosure is directed to heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems and systems and methods for falling film evaporator tube arrangements and associated components. In general, HVAC&R systems include a closed refrigeration circuit having an evaporator configured to vaporize, or evaporate, a refrigerant therein to enable the HVAC&R system to condition an interior space. By employing a falling film evaporator, the HVAC&R system may employ a reduced amount of refrigerant and/or an enhanced performance as compared to traditional flooded evaporators. Moreover, embodiments discussed herein may employ an optimized tube arrangement for tubes disposed within the falling film evaporator to reduce an amount of stress experienced by tubesheets (e.g., tubesheet stress) that support heat exchange tubes (e.g., tubes) within a shell of the falling film evaporator. Thus, a Finite Element Analysis (FEA) software, or another suitable, electronic determination, may be employed to compute (e.g., calculate, determine) an amount of stress for each tubesheet. Then, based on the tubesheet stress, a tubesheet thickness for tubesheets of the falling film evaporator may be reduced as compared to a tubesheet thickness for tubesheets of the traditional flooded evaporator discussed above. Thus, material costs and installation costs may be reduced, while proper operational safety margins and structural integrity are maintained within the HVAC&R system.

Turning now to the drawings, FIG. 1 is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system 10 in a building 12 for a typical commercial setting. The HVAC&R system 10 may include a vapor compression system 14 that supplies a chilled liquid, which may be used to cool the building 12. The HVAC&R system 10 may also include a boiler 16 to supply warm liquid to heat the building 12 and an air distribution system which circulates air through the building 12. The air distribution system can also include an air return duct 18, an air supply duct 20, and/or an air handler 22. In some embodiments, the air handler 22 may include a heat exchanger that is connected to the boiler 16 and the vapor compression system 14 by conduits 24. The heat exchanger in the air handler 22 may receive either heated liquid from the boiler 16 or chilled liquid from the vapor compression system 14, depending on the mode of operation of the HVAC&R system 10. The HVAC&R system 10 is shown with a separate air handler on each floor of building 12, but in other embodiments, the HVAC&R system 10 may include air handlers 22 and/or other components that may be shared between or among floors.

FIGS. 2 and 3 are embodiments of the vapor compression system 14 that can be used in the HVAC&R system 10. The vapor compression system 14 may circulate a refrigerant through a circuit starting with a compressor 32. The circuit may also include a condenser 34, an expansion valve (s) or device (s) 36, and a liquid chiller or an evaporator 38. The vapor compression system 14 may further include a control panel 40 that has an analog to digital (A/D) converter 42, a microprocessor 44, a non-volatile memory 46, and/or an interface board 48.

Some examples of fluids that may be used as refrigerants in the vapor compression system 14 are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407, R-134a, hydrofluoro olefin (HFO) , “natural” refrigerants like ammonia (NH3) , R-717, carbon dioxide (CO2) , R-744, or hydrocarbon based refrigerants, water vapor, or any other suitable refrigerant. In some embodiments, the vapor compression system 14 may be configured to efficiently utilize refrigerants having a normal boiling point of about 19 degrees Celsius (66 degrees Fahrenheit) at one atmosphere of pressure, also referred to as low pressure refrigerants, versus a medium pressure refrigerant, such as R-134a. As used herein, “normal boiling point” may refer to a boiling point temperature measured at one atmosphere of pressure.

In some embodiments, the vapor compression system 14 may use one or more of a variable speed drive (VSDs) 52, a motor 50, the compressor 32, the condenser 34, the expansion valve or device 36, and/or the evaporator 38. The motor 50 may drive the compressor 32 and may be powered by a variable speed drive (VSD) 52. The VSD 52 receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor 50. In other embodiments, the motor 50 may be powered directly from an AC or direct current (DC) power source. The motor 50 may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor 32 compresses a refrigerant vapor and delivers the vapor to the condenser 34 through a discharge passage. In some embodiments, the compressor 32 may be a centrifugal compressor. The refrigerant vapor delivered by the compressor 32 to the condenser 34 may transfer heat to a cooling fluid (e.g., water or air) in the condenser 34. The refrigerant vapor may condense to a refrigerant liquid in the condenser 34 as a result of thermal heat transfer with the cooling fluid. The liquid refrigerant from the condenser 34 may flow through the expansion device 36 to the evaporator 38. In the illustrated embodiment of FIG. 3, the condenser 34 is water cooled and includes a tube bundle 54 connected to a cooling tower 56, which supplies the cooling fluid to the condenser 34.

The liquid refrigerant delivered to the evaporator 38 may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser 34. The liquid refrigerant in the evaporator 38 may undergo a phase change from the liquid refrigerant to a refrigerant vapor. As shown in the illustrated embodiment of FIG. 3, the evaporator 38 may include a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. The cooling fluid of the evaporator 38 (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator 38 via return line 60R and exits the evaporator 38 via supply line 60S. The evaporator 38 may reduce the temperature of the cooling fluid in the tube bundle 58 via thermal heat transfer with the refrigerant. The tube bundle 58 in the evaporator 38 can include a plurality of tubes and/or a plurality of tube bundles. In any case, the vapor refrigerant exits the evaporator 38 and returns to the compressor 32 by a suction line to complete the cycle.

FIG. 4 is a schematic diagram of the vapor compression system 14 with an intermediate circuit 64 incorporated between condenser 34 and the expansion device 36. The intermediate circuit 64 may have an inlet line 68 that is directly fluidly connected to the condenser 34. In other embodiments, the inlet line 68 may be indirectly fluidly coupled to the condenser 34. As shown in the illustrated embodiment of FIG. 4, the inlet line 68 includes a first expansion device 66 positioned upstream of an intermediate vessel 70. In some embodiments, the intermediate vessel 70 may be a flash tank (e.g., a flash intercooler) . In other embodiments, the intermediate vessel 70 may be configured as a heat exchanger or a "surface economizer. " In the illustrated embodiment of FIG. 4, the intermediate vessel 70 is used as a flash tank, and the first expansion device 66 is configured to lower the pressure of (e.g., expand) the liquid refrigerant received from the condenser 34. During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel 70 may be used to separate the vapor from the liquid received from the first expansion device 66. Additionally, the intermediate vessel 70 may provide for further expansion of the liquid refrigerant because of a pressure drop experienced by the liquid refrigerant when entering the intermediate vessel 70 (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel 70) . The vapor in the intermediate vessel 70 may be drawn by the compressor 32 through a suction line 74 of the compressor 32. In other embodiments, the vapor in the intermediate vessel may be drawn to an intermediate stage of the compressor 32 (e.g., not the suction stage) . The liquid that collects in the intermediate vessel 70 may be at a lower enthalpy than the liquid refrigerant exiting the condenser 34 because of the expansion in the expansion device 66 and/or the intermediate vessel 70. The liquid from intermediate vessel 70 may then flow in line 72 through a second expansion device 36 to the evaporator 38.

With the above understanding of the HVAC&R system 20 in mind, FIG. 5 is a cross-sectional view of the evaporator 38 (e.g., falling film evaporator) that includes a tube layout 100 (e.g., tube arrangement) for reducing or minimizing a tubesheet thickness of tubesheets (shown in FIG. 6) of the evaporator 38. For example, as discussed above, traditional evaporators (e.g., flooded evaporators) may include tubesheets that are overdesigned or include more material (e.g., greater thicknesses) than needed for proper operation and maintenance of comparable other types of evaporators, such as the evaporator 38. As will be understood, the tube layout 100 of the evaporator 38 distributes force, traditionally applied to a lower portion of the tubesheets, across a greater vertical extent of the tubesheets. This wider distribution of force reduces an amount of stress (e.g., force divided by cross-sectional area) experienced by the tubesheets of the evaporator 38. The reduced amount of stress enables service technicians or system designers of the evaporator 38 to reduce a thickness of the tubesheets for the evaporator 38 as compared to a thickness of tubesheets for traditional flooded evaporators, thus reducing material costs for the evaporator 38.

As shown, the tube layout 100 includes a lower tube bundle 102 and an upper tube bundle 104 disposed within a shell 106 of the evaporator. Each

tube bundle

102, 104 includes heat exchange tubes 110 (e.g., tubes) that extend longitudinally into the page, as shown. The lower tube bundle 102 is disposed within a bottom portion 112 of the shell 106, while a lower edge 114 of the upper tube bundle 104 is separated from an upper edge 116 of the lower tube bundle 102 by a separation space 120. Thus, the upper tube bundle 104 is disposed within a middle portion 122 of the shell 106. However, it is to be understood that each

tube bundle

102, 104 may be located in other suitable positions within the shell 106 to evaporate refrigerant therein.

To more efficiently distribute a force applied by the tubes 110 across a greater portion of an inner height 130 of the shell 106 (and corresponding tubesheets) , as compared to a traditional flooded evaporator, the tube layout 100 includes a tube layout height 132 (e.g., vertical extent, defined between a lower edge 134 of the lower tube bundle 102 and an upper edge 136 of the upper tube bundle 104) . As shown, the tube layout height 132 is greater than 50 percent of the inner height 130 of the shell 106. For example, in some embodiments, the tube layout height 132 may be 51 percent, 60 percent, 70 percent, 80 percent, or the like, of the inner height 130 of the shell 106. Thus, the upper edge 136 of the upper tube bundle 104 extends above a horizontal midline 140 of the shell 106 (e.g., that vertically bisects the inner height 132 of the shell 106) .

Additionally, during operation of the evaporator 38, a low pressure refrigerant 150 travels through a refrigerant inlet 152 and into a distributor 154. The distributor 154 may be any suitable distributor that deposits the low pressure refrigerant 150 into the tubes 110 of the upper tube bundle 104. Thus, the low pressure refrigerant 150 exchanges thermal energy with the fluid (e.g., water) traveling through the tubes 110 as the low pressure refrigerant 150 flows on top of the upper tube bundle 104 and the lower tube bundle 102. As the low pressure refrigerant 150 absorbs thermal energy from the fluid in the tubes 110, the low pressure refrigerant 150 vaporizes. Thus, the lower tube bundle 102 includes a lower tube bundle width 162 defined between end tubes 164 of the lower tube bundle 104, and the upper tube bundle 104 similarly includes an upper tube bundle width 166 defined between end tubes 168 of the upper tube bundle 104. By having an upper tube bundle width 166 that is less than the lower tube bundle width 162, the tube layout 100 provides vapor channels 170 between the upper tube bundle 104 and an inner surface 172 of the shell, such that vaporized low pressure refrigerant 174 may travel therethrough. Additionally, the present embodiment of the evaporator 38 includes mesh eliminators 176 to remove entrained liquid droplets from the vaporized low pressure refrigerant 174 on its way out of the shell 106 and to the compressor 32.

Thus, when a fluid is traversing through the tubes 110 and moving within water boxes attached to the tubesheets, and as the low pressure refrigerant 150 flows within the shell 106, the tubesheets may receive and/or absorb forces from the tubes 110 at least along portions of the tubesheets corresponding to the tube layout height 132. Thus, the tubesheets may more evenly distribute the force throughout a greater cross-sectional area of the tubesheets, as well as components coupled or in contact with the tubesheets, when the tube layout 100 extends above the horizontal midline 140 of the shell 106.

FIG. 6 is a side schematic view of the evaporator 38 having the tube layout 100 for enabling a reduction in tubesheet thickness 196 of tubesheets 198 of the evaporator 38. For example, as shown, a first water box 200 is secured to a first end 202 of the shell 106, and a second water box 204 is secured to a second end 206 of the shell 106. Additionally, the shell 106 has the refrigerant inlet 152 and a refrigerant outlet 210, with the lower tube bundle 102 and the upper tube bundle 104 positioned within the shell 106. In some embodiments, the refrigerant inlet 152 is centrally positioned relative to the opposed ends 202 and 206 of the shell 106. However, in other embodiments, the refrigerant inlet 152 may be non-centrally positioned relative to the opposed ends 202 and 206 of the shell 106, like the illustrated refrigerant outlet 210. Thus, during operation, the low pressure refrigerant 150 travels into the shell 106 via the refrigerant inlet 152 and into the distributor 154 for distribution across the tubes 110 of the tube layout 100. The tubes 110 enable a transfer of thermal energy to the low pressure refrigerant to transform the low pressure refrigerant 150 into vaporized low pressure refrigerant 174, which travels up through the shell 106 and out of the refrigerant outlet 210 on its way to the compressor 32.

To provide the thermal energy to the low pressure refrigerant 150, the evaporator 38 supplies a cooling fluid 220 (e.g., warm water) through an inlet 224 of a lower chamber 222 of the first water box 200. Then, the cooling fluid 220 is directed through the tubes 110 of the lower tube bundle 104 for a first pass through the shell 106. Additionally, the cooling fluid 220 is directed by the second water box 204 into the tubes 110 of the upper tube bundle 104 for a second pass though the shell 106, and is directed out of the shell 106 through an outlet 228 of a second chamber 230 of the first water box 200 (e.g., as cooled water) . While the illustrated embodiment of FIG. 6 shows the evaporator 38 as having two passes for the cooling fluid 220, it should be recognized that, in other embodiments, the evaporator 38 may be configured to direct the cooling fluid 220 using any suitable number of passes (e.g., one, two, four, five, six, seven, eight, nine, ten, or more passes) .

Moreover, to provide structural support to components of the evaporator 38, the tubesheets 198 of the evaporator 38 include a first tubesheet 240 disposed between the first waterbox 200 and the tubes 110 at the first end 202 of the shell 106 and a second tubesheet 242 disposed between the second waterbox 204 and the tubes 110 at the second end 206 of the shell 106. For example, the tubesheets 198 support the lower tube bundle 102 and the upper tube bundle 104 within the shell 106 at longitudinal ends 248 of the tubes 110 of the lower tube bundle 102 and the upper tube bundle 104. Additionally, the tubesheets 198 support a portion of a weight of the first waterbox 200 and the second waterbox 204. In addition to the weight of components, the tubesheets 198 also experience forces from the cooling fluid 220 contacting the tubesheets 198, pushing against portions of the first waterbox 200 and the second waterbox 204, as well as pressure through the tubes 110. Moreover, the low pressure refrigerant 150 flowing down through the shell 106, and the vaporized low pressure refrigerant flowing up through the tubes 110 may apply force to the tubes 110, which may transmit the force to the tubesheets 198.

To support each type of force applied to the tubesheets 198, both when the evaporator 38 is operating and when the evaporator 38 is not operating, the tubesheets 198 are designed with the illustrated tubesheet thickness 196 respectively defined between a first surface 250 and a second surface 252 of the tubesheets 198. For example, the tubesheets 198 may be formed of any suitable structurally sound and/or corrosion-resistant material, including steel, other iron–carbon alloy phases, or copper. In some embodiments, tubesheets of greater thicknesses have a greater structural integrity, including a greater yield strength and/or yield point than those of thinner thicknesses. As used herein, the yield strength refers to the stress (e.g., force applied over a cross-sectional area) at which a tubesheet initiates plastic deformation, and the stress point refers to the stress at which a tubesheet initiates at least partial elastic deformation (e.g., non-linear or non-reversible deformation) . Further, the tubesheets 198 may dissipate stresses received from components of the evaporator 38 to other components of the evaporator 38 or in contact with the evaporator 38, such as terrain 256 on which the evaporator 38 is disposed or connections to other equipment of the HVAC&R system 10.

However, because tubesheets of a greater thickness include a greater amount of material, the tubesheets of the greater thickness cost more to procure and/or take longer to install (e.g., due to increased amount of time required for drilling openings or forming holes through the tubesheets) . Thus, the present disclosure recognizes an important relationship between the structural integrity of the tubesheets 198, and the tubesheet thickness 196. Accordingly, the tube layout 100 includes the tubes 110 that extend above the horizontal midline 140 of the shell 106 to optimize the area of each tubesheet 198 that receives forces from the tubes 110,

water boxes

200, 204, and fluids, as compared to traditional flooded evaporators that focus stress on a lower portion of the tubesheets therein. Thus, the tube layout 100 enables the tubesheets 198 to be decreased in tubesheet thickness 196 while maintaining the desired amount of structural integrity to lower material and installation costs. Additionally, it is to be understood that the present techniques may also be used to increase the structural integrity of the tubesheets 198 for a given tubesheet thickness 196.

To determine the stress within the tubesheets 198, a service technician or system designer may model the evaporator 38 having the tube layout 100 via Finite Element Analysis (FEA) software on a computing device, thus enabling the service technician or the system designer to determine a reduction in tubesheet thickness for the evaporator 38 as compared to tubesheets for traditional flooded evaporators. For example, FIG. 7 is a schematic diagram of a FEA screen overlay 300 for a modeled tubesheet 302 having openings 304 to receive the tubes 110 of the tube layout 100 discussed above. In particular, the FEA screen overlay 300 may be included on an electronic display of any suitable computing device (e.g., laptop computer, desktop computer, tablet, etc. ) having a processor and memory therein, such as the illustrated computing device 310.

The embodiment of the FEA screen overlay 300 is a computation of deformation of the modeled tubesheet 302. As discussed above, a tubesheet may deform in response to structural stress applied to the tubesheet. Plastic (or reversible) deformation may occur in response to stresses above a yield threshold of the modeled tubesheet 302, which may occur during normal operation of the HVAC&R system 10. The illustrated view of the modeled tubesheet 302 is taken along the longitudinal axis of a shell of the evaporator, such that stress applied to both a front surface and a back surface of the modeled tubesheet 302 is determined via FEA.

For example, the modeled tubesheet 302 experiences a plurality of deformation amounts 318, including a first amount of deformation 320 illustrated in an upper portion 322 of the modeled tubesheet 302. The first amount of deformation 320 may be the highest amount of deformation experienced by the modeled tubesheet 302. However, in embodiments of the HVAC&R system 10 in which the FEA screen overlay 300 is modeling a portion of a 250 ton chiller (e.g., having 250 refrigeration tons) , the first amount of deformation 320 may be less than 1 mm, 0.9 mm, 0.8 mm, 0.7 mm, or lower. In contrast, a comparable, traditional flooded evaporator may experience a highest amount of deformation that is greater than 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, or higher.

Additionally, the plurality of deformation amounts 318 includes: a second amount of deformation 326 represented circumferentially surrounding the first amount of deformation 320, a third amount of deformation 328 represented circumferentially surrounding the second amount of deformation 326, a fourth amount of deformation 330 represented circumferentially surrounding the third amount of deformation 328, and a fifth amount of deformation 332 represented circumferentially surrounding the fourth amount of deformation 330. The illustrated plurality of deformation amounts 318 decrease from the value of the first amount of deformation 320 to the fifth amount of deformation 332. For example, a range of deformation experienced by the modeled tubesheet 302 may span from 1 mm to 0.5 mm, 1 mm to 0 mm, 1 mm to -0.5 mm, 1 mm to -1 mm, 1 mm to -2 mm, etc., where negative values of amounts of deformation are in an opposite direction from positive values of amounts of deformation. Additionally, it is to be understood that the denotations between amounts of deformation are merely exemplary, such that other intervals, levels, or illustrations of stress are also in line with the disclosed techniques.

However, compared to a corresponding plurality of deformation amounts for a traditional flooded evaporator having tubes focused in a small portion of the tubesheets, the range of deformation experienced by the modeled tubesheet 302 having the tube layout 100 is considerably less. For example, the range of deformation experienced by the tubesheet of the traditional flooded evaporator may span from 2 mm to -4 mm, 1.5 mm to -3.5 mm, 1.5 mm to -2.5 mm, etc. Thus, the tube layout 100 discussed herein utilizes a greater vertical extent of the modeled tubesheet 302 to distribute forces therein, thus reducing amounts of deformation experienced by the modeled tubesheet 302 and enabling a reduction in tubesheet thickness.

Further, FIG. 8 is another schematic diagram of a FEA screen overlay 360 for the modeled tubesheet 302 discussed above. Similar to FIG. 7, the FEA screen overlay 360 may also be included on the electronic display of the computing device 310 or any other suitable computing device. In general, FEA may be employed by software of the computing device 310 to compute stress experienced by the modeled tubesheet 302. Thus, the FEA for the stress of the modeled tubesheet 302 during operation is shown in the FEA screen overlay 360.

For example, the modeled tubesheet 302 experiences a plurality of stress amounts 362, including a first amount of stress 370 illustrated in the upper portion 322 of the modeled tubesheet 302. The first amount of stress 370 may be the highest amount of stress experienced by the modeled tubesheet 302. However, in embodiments of the HVAC&R system 10 in which the FEA screen overlay 360 is modeling a portion of the 250 ton chiller, the first amount of stress 370 may be less than 250 MPa, 200 MPa, 190 MPa, 175 MPa, or lower. Additionally, the plurality of stress amounts 362 includes: a second amount of stress 372 represented circumferentially surrounding the first amount of stress 370, a third amount of stress 374 represented circumferentially surrounding the second amount of stress 372, and a fourth amount of stress 376 represented circumferentially surrounding the third amount of stress 374.

The illustrated plurality of stress amounts decrease from the value of the first amount of stress 370 to the fourth amount of stress 376. For example, a range of stress experienced by the modeled tubesheet 302 (e.g., between the first amount of stress 370 and the fourth amount of stress 376) may span from 200 MPa to 0 MPa, 200 MPa to 1 MPa, 190 MPa to 1 MPa, 190 MPa to 5 MPa, 180 MPa to 10 MPa, etc. Further, it is to be understood that the denotations between amounts of stress are merely exemplary, such that other intervals, levels, or illustrations of stress are also in line with the disclosed techniques. In certain embodiments, a corresponding plurality of stress amounts for a traditional flooded evaporator may have a similar range as the range of stress values experienced by the modeled tubesheet 302 having the tube layout 100. However, the stress values for the traditional flooded evaporator may be more “top heavy” or skewed upwards towards a highest level of stress computed for the traditional flooded evaporator tubesheet, such that an average amount of the stress experienced by the traditional flooded evaporator tubesheet is greater than that of the modeled tubesheet 302. As such, the tube layout 100 discussed herein utilizes a greater vertical extent of the modeled tubesheet 302 to distribute forces therein, thus reducing amounts of stress experienced by the modeled tubesheet 302. An exemplary set of averages for the tube layout 100 and the traditional flooded evaporator tube layout is discussed below with reference to Table 1.

Additional stresses may also be calculated for the modeled tubesheet 302 as compared to tubesheets for traditional flooded evaporators. Indeed, an exemplary embodiment of the deformation and stresses for tubes and tubesheets for a falling film evaporator as compared to a flooded evaporator for a 250 ton (e.g., ton of refrigeration) chiller is shown below in Table 1. In some embodiments, the tube layout 100 of Table 1 is included in the evaporator 38 of the HVAC&R system 10 discussed above.

Table 1. Stresses and Deformation of Tube Layouts

A first row of Table 1 includes a comparison of tube stress in MPa (e.g., average tube stress across the tubesheets) for the modeled tubesheet 302 versus a tubesheet having a traditional flooded evaporator tube layout. Additionally, a second row of Table 1 includes a comparison of the tubesheet deformation in mm (e.g., average tubesheet deformation across the tubesheets) for the modeled tubesheet 302 versus the tubesheet having the traditional flooded evaporator tube layout, as visualized by FIG. 7. Further, a third row of Table 1 includes a comparison of tubesheet stress in MPa (e.g., average tubesheet stress across the tubesheets) for the modeled tubesheet 302 versus the tubesheet having the traditional flooded evaporator tube layout, as visualized by FIG. 8. As shown by a third column of percentage differences, the respective values for the modeled tubesheet 302 are considerably lower than the respective values for the tubesheet having the traditional flooded evaporator tube layout, emphasizing the effectiveness in reducing tubesheet stress acquired by using the disclosed tube layout 100.

Further, in certain embodiments for chillers of various tonnages having a tube side pressure (e.g., pressure within the tubes 110) of 150 psi, the tubesheet thickness may be optimized between 1.6 inches and 1.7 inches, between 1.6 inches and 1.65 inches, or at 1.625 inches, etc. Additionally, in certain embodiments for chillers of various tonnages having a tube side pressure of 300 psi, the tubesheet thickness may be optimized at between 2.25 inches and 2.75 inches, between 2.4 inches and 2.6 inches, or at 2.5 inches, etc. Thus, FEA considerations may be employed to optimally determine a balance between material costs and structural integrity to provide cost savings for the evaporator coil 38 at a desired amount of structural integrity.

The present disclosure recognizes the importance of FEA used to calculate various stresses for the modeled tubesheet 302 that enable determination of a reduction in tubesheet width that provides a tubesheet having desired amounts of structural integrity. For example, FEA may be applied to the tubesheets 198 of the evaporator 38 of the HVAC&R system 10, or any other suitable falling film evaporator based on the modeled tubesheet 302. Thus, the tubesheets 198 may be designed with a reduced or minimized tubesheet thickness 196 based on the results presented in the FEA screen overlay 300 and the FEA screen overlay 360. For example, the tubesheet thickness 196 may be reduced or minimized based on a magnitude of stress experienced by the tubesheets 198, such that the tubesheet thickness 196 can be reduced while the magnitude of stress remains below a threshold stress value. Moreover, in some embodiments, the tubesheet stress may be determined based at least in part on the tubesheet deformation and/or the tube stress.

In some embodiments, the potential reduction in tubesheet thickness is directly proportional to a potential reduction (e.g., percentage difference) in tubesheet stress compared to a computation of tubesheet stress for a traditional flooded evaporator of similar size, capacity, etc. For example, based on the reduction in Tubesheet Stress shown in Table 1, the modeled tubesheet 302 having the tube layout 100 may be reduced in thickness by 11.8 percent as compared to a tubesheet having a traditional flooded evaporator tube layout. Thus, traditional flooded evaporators experiences greater stress in concentrated areas, while falling film evaporators include more even distribution of forces throughout tubesheets, enabling a lower minimization of tubesheet thickness to reduces material cost and installation time (e.g., such as drilling operations) .

Accordingly, the present techniques are directed to a tube layout design for an evaporator (e.g., falling-film evaporator) . The tube layout design includes a lower tube bundle and an upper tube bundle each disposed within a shell of the evaporator. The lower tube bundle may be disposed within a lower curve of the shell of the evaporator. The upper tube bundle may be vertically spaced from the lower tube bundle, and extend above a horizontal midline of the shell. As such, the upper tube bundle may have a greater height and a lesser width compared to an upper tube bundle of heat exchange tubes in a traditional flooded evaporator to enable refrigerant that evaporates on the tubes to rise though mesh eliminators and exit the shell. The tube layout therefore provides a tube hole area in the tubesheet that may be more evenly distributed throughout a height of the tubesheet than a traditional flooded evaporator. For example, the upper tube bundle may extend above a horizontal midline of the tubesheet, as compared to tube layout designs for traditional flooded evaporators in which an upper tube bundle does not extend above the horizontal midline. Accordingly, by using the tube layout design (e.g., tube arrangement) , deformation and stress on the tubes and the tubesheets is reduced, thus allowing for a reduction in a thickness of tubesheets as compared to tubesheets used in traditional flooded evaporators.

While only certain features and embodiments of the present disclosure 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, 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 re-sequenced 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 disclosure. Furthermore, in an effort to provide a concise description of the 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 disclosure, or those unrelated to enabling the claimed features) . 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

A heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, comprising:

a falling film evaporator configured to vaporize a low pressure refrigerant liquid into a low pressure refrigerant gas, wherein the falling film evaporator comprises:

a shell comprising a first tubesheet disposed at a first end portion of the shell and a second tubesheet disposed at a second end portion of the shell；

a lower tube bundle disposed within a bottom portion of the shell and having a first lower bundle end and a second lower bundle end respectively supported by the first tubesheet and the second tubesheet； and

an upper tube bundle disposed above the lower tube bundle within the shell and having a first upper bundle end and a second upper bundle end respectively supported by the first tubesheet and the second tubesheet, wherein an upper edge of the upper tube bundle extends above a horizontal midline of the shell to enable the upper tube bundle and the lower tube bundle to distribute a force across a vertical extent of the first tubesheet and the second tubesheet.
The HVAC&R system of claim 1, wherein the falling film evaporator comprises a tube side pressure of 150 psi, and wherein the first tubesheet and the second tubesheet each comprise a tubesheet thickness between 1.6 inches and 1.7 inches.
The HVAC&R system of claim 1, wherein the falling film evaporator comprises a tube side pressure of 150 psi, and wherein the first tubesheet and the second tubesheet each comprise a tubesheet thickness between 1.6 inches and 1.65 inches.
The HVAC&R system of claim 1, wherein the falling film evaporator comprises a tube side pressure of 150 psi, and wherein the first tubesheet and the second tubesheet each comprise a tubesheet thickness of 1.625 inches.
The HVAC&R system of claim 1, wherein the falling film evaporator comprises a tube side pressure of 300 psi, and wherein the first tubesheet and the second tubesheet each comprise a tubesheet thickness of 2.5 inches.
The HVAC&R system of claim 1, wherein the lower tube bundle and the upper tube bundle are each configured to flow a fluid that transfers heat to the low pressure refrigerant liquid to vaporize the low pressure refrigerant liquid into the low pressure refrigerant gas.
The HVAC&R system of claim 1, wherein the lower tube bundle comprises a lower tube bundle width, wherein the upper tube bundle comprises an upper tube bundle width, and wherein the lower tube bundle width is greater than the upper tube bundle width.
The HVAC&R system of claim 1, wherein a tubesheet thickness of the first tubesheet is minimized based on a calculated amount of stress on the first tubesheet and based on a calculated amount of stress on a modeled tubesheet of a flooded evaporator.
The HVAC&R system of claim 1, wherein a tubesheet thickness of each of the first tubesheet and the second tubesheet is minimized based on a calculated amount of stress on each of the first tubesheet and the second tubesheet.
The HVAC&R system of claim 9, wherein the calculated amount of stress on each of the first tubesheet and the second tubesheet is respectively calculated via computational fluid dynamics based at least in part on a calculated amount of stress on tubes of the lower tube bundle and the upper tube bundle, and based at least in part on a calculated amount of deformation of the first tubesheet and the second tubesheet.
A method of designing a falling film evaporator, comprising:

determining, via a processor of a computing device, a tubesheet stress on a tubesheet of the falling film evaporator, wherein the tubesheet is configured to support an end of a lower tube bundle and an upper tube bundle disposed within a shell, and wherein the upper tube bundle extends above a horizontal midline of the shell, and

calculating, via the processor, a thickness of the tubesheet based on the tubesheet stress.
The method of claim 11, comprising determining, via the processor, a tubesheet deformation on the tubesheet of the falling film evaporator, wherein the tubesheet stress is determined based at least in part on the tubesheet deformation.
The method of claim 11, comprising determining, via the processor, a tube stress on tubes of the lower tube bundle and the upper tube bundle, wherein the tubesheet stress is determined based at least in part on the tube stress.
The method of claim 11, comprising determining, via the processor, an additional tubesheet stress on a tubesheet of a flooded evaporator, wherein the flooded evaporator comprises an upper tube bundle that does not extend above a horizontal midline of a shell of the flooded evaporator, and comparing, via the processor, the tubesheet stress of the falling film evaporator to the additional tubesheet stress of the flooded evaporator to determine a percentage different therebetween, wherein the thickness of the tubesheet is calculated based at least in part on the percentage difference.
The method of claim 14, wherein the thickness of the tubesheet of the falling film evaporator is less than a thickness of the tubesheet of the flooded evaporator by the percentage difference.