Patent Publication Number: US-2021190432-A1

Title: Falling film heat exchanger

Description:
BACKGROUND 
     This application relates generally to a falling film heat exchanger that may be used in air conditioning and refrigeration applications. 
     Vapor compression systems utilize a working fluid, typically referred to as a refrigerant that 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 a falling film heat exchanger (e.g., evaporator) having a refrigerant distributor configured to distribute the refrigerant to an evaporating tube bundle. For example, certain refrigerant distributors include a perforated plate having holes that enable the refrigerant to flow through the perforated plate to the evaporating tubes. Unfortunately, typical perforated plates may not evenly distribute the refrigerant to the evaporating tubes, thereby reducing the efficiency of the vapor compression system. 
     SUMMARY 
     In an embodiment of the present disclosure, a heat exchanger for a heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) system includes a shell having an inlet configured to receive refrigerant and an outlet configured to output the refrigerant. The heat exchanger also includes a refrigerant distributor disposed within the shell, and multiple evaporating tubes disposed within the shell and positioned below the refrigerant distributor. The refrigerant distributor includes a perforated plate having multiple holes, each hole extends from a top surface of the perforated plate to a bottom surface of the perforated plate, and a center point of each hole is substantially aligned with a centerline of a respective evaporating tube. 
     In another embodiment of the present disclosure, a heat exchanger for an HVAC&amp;R system includes a shell having an inlet configured to receive refrigerant and an outlet configured to output the refrigerant. The heat exchanger also includes a refrigerant distributor disposed within the shell, and multiple evaporating tubes disposed within the shell and positioned below the refrigerant distributor. The refrigerant distributor includes a perforated plate having multiple holes each extending substantially along a vertical axis, each hole extends from a top surface of the perforated plate to a bottom surface of the perforated plate, and a first portion of the top surface is positioned above a second portion of the top surface along the vertical axis. 
     In a further embodiment of the present disclosure, a heat exchanger for an HVAC&amp;R system includes a shell having an inlet configured to receive refrigerant and an outlet configured to output the refrigerant. The heat exchanger also includes a refrigerant distributor disposed within the shell, and multiple evaporating tubes disposed within the shell and positioned below the refrigerant distributor. Each evaporating tube extends along a longitudinal axis, the refrigerant distributor includes a perforated plate having multiple holes, each hole extends from a top surface of the perforated plate to a bottom surface of the perforated plate, and the holes are arranged in at least one row. In addition, spacings between adjacent holes of the at least one row vary along the longitudinal axis, and/or sizes of adjacent holes of the at least one row vary along the longitudinal axis. 
     In another embodiment of the present disclosure, a heat exchanger for an HVAC&amp;R system includes a shell having an inlet configured to receive refrigerant and an outlet configured to output the refrigerant. The heat exchanger also includes a refrigerant distributor disposed within the shell, and multiple evaporating tubes disposed within the shell and positioned below the refrigerant distributor. Each evaporating tube extends along a longitudinal axis. In addition, the heat exchanger includes a spray header disposed within the shell and positioned above the refrigerant distributor. The spray header has multiple openings configured to output the refrigerant toward the refrigerant distributor, and the openings are arranged along a lateral axis, substantially perpendicular to the longitudinal axis. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of an embodiment of a building that may utilize a heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) system in a commercial setting, in accordance with an aspect of the present disclosure; 
         FIG. 2  is a perspective view of an embodiment of a vapor compression system that may be used in the HVAC&amp;R system of  FIG. 1 ; 
         FIG. 3  is a schematic diagram of an embodiment of a vapor compression system that may be used in the HVAC&amp;R system of  FIG. 1 ; 
         FIG. 4  is a schematic diagram of an embodiment of a falling film evaporator that may be used in a vapor compression system, in which the falling film evaporator includes a refrigerant distributor; 
         FIG. 5  is a perspective view of an embodiment of a perforated plate that may be used in the refrigerant distributor of  FIG. 4 ; 
         FIG. 6  is a detailed cross-sectional view of an embodiment of a perforated plate that may be used in the refrigerant distributor of  FIG. 4 ; 
         FIG. 7  is a top view of an embodiment of a perforated plate that may be used in the refrigerant distributor of  FIG. 4 ; 
         FIG. 8  is a schematic diagram of a portion of an embodiment of a falling film evaporator that may be used in the HVAC&amp;R system of  FIG. 1 ; 
         FIG. 9  is a top view of another embodiment of a perforated plate that may be used in the refrigerant distributor of  FIG. 4 ; 
         FIG. 10  is a top view of a further embodiment of a perforated plate that may be used in the refrigerant distributor of  FIG. 4 ; and 
         FIG. 11  is a schematic diagram of a portion of an embodiment of a falling film evaporator that may be used in the HVAC&amp;R system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings,  FIG. 1  is a perspective view of an embodiment of a building  12  that may utilize a heating, ventilation, air conditioning, and refrigeration (HVAC&amp;R) system  10  in a commercial setting. The HVAC&amp;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&amp;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 may 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&amp;R system  10 . The HVAC&amp;R system  10  is shown with a separate air handler on each floor of building  12 , but in other embodiments, the HVAC&amp;R system  10  may include air handlers  22  and/or other components that may be shared between or among floors. 
       FIG. 2  is a perspective view of an embodiment of a vapor compression system  14  that may be used in the HVAC&amp;R system of  FIG. 1 , and  FIG. 3  is a schematic diagram of an embodiment of a vapor compression system  14  that may be used in the HVAC&amp;R system of  FIG. 1 . The vapor compression system  14  of  FIGS. 2 and 3  may circulate a refrigerant through a circuit starting with a compressor  32 . The circuit may also include a condenser  34 , 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 system  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 (e.g., ammonia (NH 3 ), R-717, carbon dioxide (CO 2 ), 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 (VSD)  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. 
     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  60 S and a return line  60 R 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  60 R and exits the evaporator  38  via supply line  60 S. 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  may include multiple tubes and/or multiple 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 an embodiment of a falling film evaporator  64  (e.g., falling film heat exchanger) that may be used in a vapor compression system. For example, the falling film evaporator  64  may be used in place of the expansion device and the evaporator of the vapor compression systems of  FIGS. 2 and 3 . In the illustrated embodiment, the falling film evaporator  64  includes a shell  66  having an inlet  68  and an outlet  70 . The inlet  68  is configured to be fluidly coupled to a discharge port of a condenser (e.g., via a discharge passage), and the outlet  70  is configured to be fluidly coupled to a suction port of a compressor (e.g., via a suction line). The inlet  68  is configured to receive refrigerant from the discharge port of the condenser, and the outlet  70  is configured to output the refrigerant to the suction port of the compressor. In the illustrated embodiment, the shell  66  has a substantially circular cross-section. However, it should be appreciated that in alternative embodiments, the shell may have other cross-sectional shapes, such as elliptical or polygonal, among others. 
     In the illustrated embodiment, the falling film evaporator  64  includes a liquid refrigerant region  74  extending from the inlet  68  to a refrigerant distributor  78  disposed within the shell  66 . The liquid refrigerant region  74  is positioned above the refrigerant distributor  78  along a vertical axis  80 , and evaporating tubes  82  are positioned below the refrigerant distributor  78  along the vertical axis  80 . As illustrated, the evaporating tubes  82  are positioned within an evaporator region  84  of the shell  66 . The refrigerant distributor  78  extends along a longitudinal axis  86  and along a lateral axis  88 . In the illustrated embodiment, the longitudinal axis  86  corresponds to the direction of extension of the evaporating tubes  82  (e.g., the orientation of the longitudinal axes of the evaporating tubes). Accordingly, the evaporating tubes  82  extend along the longitudinal axis  86 . 
     During operation of the vapor compression system, liquid refrigerant from the condenser enters the shell  66  through the inlet  68 . The liquid refrigerant then flows through the refrigerant distributor  78 , which distributes liquid refrigerant droplets to the evaporating tubes  82 . Contact between the liquid refrigerant droplets and the evaporating tubes  82  induces the liquid droplets to vaporize, thereby absorbing heat from the cooling fluid within the evaporating tubes. As a result, the temperature of the cooling fluid within the evaporating tubes is reduced. The vaporized refrigerant flows from the evaporator region  84  to the outlet  70  and then to the suction port of the compressor (e.g., via a suction line). The refrigerant distributor  78  also establishes a pressure differential between the liquid refrigerant region  74  and the evaporator region  84  sufficient to facilitate efficient evaporation of the refrigerant in the evaporator region. 
       FIG. 5  is a perspective view of an embodiment of a perforated plate  90  that may be used in the refrigerant distributor of  FIG. 4 . In the illustrated embodiment, the perforated plate  90  includes multiple holes  92 . As discussed in detail below, each hole  92  extends from a top surface of the perforated plate  90  to a bottom surface of the perforated plate  90 , thereby enabling the refrigerant to flow through the perforated plate. The holes may be arranged in any suitable pattern to control refrigerant flow through the perforated plate. In addition, the size of the holes and/or the number of holes may be particularly selected to control droplet formation and/or the pressure differential between the liquid refrigerant region and the evaporator region of the falling film evaporator. 
       FIG. 6  is a detailed cross-sectional view of an embodiment of a perforated plate  91  that may be used in the refrigerant distributor  78  of  FIG. 4 . As illustrated, the perforated plate  91  includes multiple holes  92  that facilitate flow of refrigerant from the liquid refrigerant region to the evaporator region. Each hole  92  extends along the vertical axis  80  from a top surface  94  of the perforated plate  91  to a bottom surface  96  of the perforated plate  91 . In the illustrated embodiment, the perforated plate includes protrusions  98  extending from the bottom surface  96  of the perforated plate  91 . As illustrated, each protrusion  98  is positioned at an outlet  100  of a respective hole  92 . The protrusions  98  are configured to induce the refrigerant flowing through the holes  92  to form droplets, which then fall downwardly under the influence of gravity into the evaporator region. 
     A height  102  of each protrusion  98  may be particularly selected to establish a target droplet size. In addition, a profile (e.g., shape) of each protrusion may be particularly configured to establish a target droplet size. For example, in certain embodiments, the protrusion may extend about an entire periphery (e.g., circumference) of the hole outlet. However, in alternative embodiments, the protrusion may extend about a portion of the periphery (e.g., about 5 percent to about 95 percent, about 10 percent to about 91 percent, about 20 percent to about 80 percent, about 30 percent to about 70 percent, or about 40 percent to about 60 percent, etc.), and/or multiple protrusions may be positioned at the outlet of at least one hole. In certain embodiments, at least one protrusion may be positioned at the outlet of each hole. However, in alternative embodiments, protrusion(s) may be positioned at a portion of the hole outlets. Furthermore, in certain embodiments, the heights and/or profiles of the protrusions may be substantially the same as one another, or at least a portion of the protrusions may have different heights and/or profiles. 
     In certain embodiments, the holes and the protrusions may be formed by a stamping process. For example, during the stamping process, projections of a die may engage a solid plate, thereby displacing material of the solid plate to form the holes. The projections may be particularly configured such that the displaced material forms the protrusions on the bottom surface of the plate. For example, the shape and/or configuration of each projection may be particularly selected such that a respective protrusion having a target height and/or profile is formed. In certain embodiments, the protrusions may be further shaped by post-stamping process(es), such as grinding and/or trimming, among others. In further embodiments, the protrusions may be formed separately and coupled to the bottom surface of the perforated plate (e.g., by welding, by adhesively bonding, etc.). It should be appreciated that the protrusions may be employed on any of the embodiments disclosed herein, or the protrusions may be omitted. 
       FIG. 7  is a top view of an embodiment of a perforated plate  93  that may be used in the refrigerant distributor  78  of  FIG. 4 . In the illustrated embodiment, the holes  92  are arranged in a first row  104  and a second row  106 . As illustrated, the first row  104  is aligned (e.g., substantially aligned) with a corresponding first evaporating tube  108 , and the second row  106  is aligned (e.g., substantially aligned) with a corresponding second evaporating tube  108 . In addition, a center point  112  of each hole  92  is aligned (e.g., substantially aligned) with a centerline  114  of a respective evaporating tube  82 . As illustrated, the center point  112  of each hole  92  of the first row  104  is aligned (e.g., substantially aligned) with the centerline  114  of the first evaporating tube  108 , and the center point  112  of each hole  92  of the second row  106  is aligned (e.g., substantially aligned) with the centerline  114  of the second evaporating tube  110 . Because the center point of each hole is aligned (e.g., substantially aligned) with the centerline of a respective evaporating tube, the liquid droplet formed by the refrigerant flow through the hole may impact the center of the tube. As a result, the quantity of liquid refrigerant that engages the surface of the respective tube may be increased, as compared to a liquid droplet that impacts a side of the tube (e.g., offset from the center), thereby increasing the efficiency of the evaporation process. 
     As used herein, aligned and substantially aligned refer to alignment along the lateral axis  88  within an offset tolerance. For example, the offset tolerance may be between about 0.1 mm and about 5 mm, between about 0.2 mm and about 2 mm, or between about 0.5 mm and about 1 mm. By way of further example, the offset tolerance may be between about 0.5 percent and about 5 percent, between about 1 percent and about 4 percent, or between about 2 percent and about 3 percent of the lateral extent (e.g., diameter) of the respective hole. In the illustrated embodiment, the evaporating tubes and the rows of holes extend along the longitudinal axis  86 . However, it should be appreciated that in alternative embodiments, the evaporating tubes and the rows of holes may be angled relative to the longitudinal axis. Furthermore, while two rows of holes are shown in the illustrated embodiment, it should be appreciated that the perforated plate may include more or fewer rows of holes (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more). Furthermore, it should be appreciated that one or more evaporating tubes may be positioned between adjacent rows of holes along the lateral axis  88 . In certain embodiments, each row of holes may be aligned with a respective evaporating tube of the top row of the evaporating tube bundle (e.g., the row of evaporating tubes positioned closest to the perforated plate). However, it should be appreciated that in alternative embodiments, one or more rows of holes may be aligned with respective evaporating tube(s) of a lower row (e.g., the second row, the third row, etc.) of the evaporating tube bundle. It should be appreciated that the hole/evaporating tube alignment may be utilized on any of the embodiments disclosed herein, or at least a portion of the holes may not be aligned with the respective evaporating tube(s). 
       FIG. 8  is a schematic diagram of a portion of an embodiment of a falling film evaporator  64 . In the illustrated embodiment, multiple evaporating tubes  82  extend along the longitudinal axis  86 . While three evaporating tubes  82  are shown in the illustrated embodiment, it should be appreciated that the falling film evaporator may include more (e.g., significantly more) evaporating tubes in certain embodiments. As illustrated, the evaporating tubes  82  are supported by a pair of tube sheets  116 , in which each tube sheet  116  extends along the vertical axis  80  and along the lateral axis  88 . While the illustrated embodiment includes two tube sheets  116 , it should be appreciated that in alternative embodiments, the heat exchanger may include more or fewer tube sheets. 
     In the illustrated embodiment, the perforated plate  95  of the refrigerant distributor  78  is positioned above the evaporating tubes  82  along the vertical axis  80 . The perforated plate  95  includes multiple holes  92  configured to facilitate flow of the refrigerant from the liquid refrigerant region  74  to the evaporator region  84 . As illustrated, each hole  92  extends substantially along the vertical axis  80 . As used herein, substantially along the vertical axis refers to an angle of about 0 degrees to about 45 degrees, about 0 degrees to about 30 degrees, about 0 degrees to about 20 degrees, or about 0 degrees to about 15 degrees relative to the vertical axis  80 . In the illustrated embodiment, the perforated plate  95  is curved (e.g., arcuate) to establish a substantially even distribution of refrigerant across the top surface  94  of the perforated plate  95 . For example, refrigerant may be directed toward a central region of the perforated plate (e.g., via a refrigerant header), and the refrigerant may flow to the distal ends of the plate under the influence of gravity, thereby substantially evenly distributing the refrigerant across the perforated plate. 
     The perforated plate  95  may be particularly configured to control the flow of refrigerant across the top surface  94 . For example, a height  118  of a maximum vertical extent  120  of the perforated plate  95  relative to a minimum vertical extent  122  of the perforated plate  95  along the vertical axis  80  may be particularly selected to control refrigerant distribution. While the perforated plate  95  forms a single continuous arc in the illustrated embodiment, it should be appreciated that in alternative embodiments, the perforated plate may form other suitable shapes. For example, in certain embodiments, the perforated plate may form substantially linear segments between the longitudinal center of the perforated plate (e.g., at the maximum vertical extent of the perforated plate) and the distal ends of the perforated plate (e.g., at the minimum vertical extent of the perforated plate). In addition, the perforated plate may include multiple curved and/or linear segments to establish a desired shape/profile. For example, in embodiments in which refrigerant is directed toward multiple longitudinal positions along the perforated plate, the perforated plate may include a peak at each longitudinal position. 
     While the illustrated perforated plate  95  includes a shaped/profiled top surface  94  and a shaped/profiled bottom surface  96 , it should be appreciated that in alternative embodiments, the bottom surface of the perforated plate may be substantially flat, and the refrigerant distribution may be controlled by the shape/profile of the top surface. Furthermore, in certain embodiments, the shape/profile of the perforated plate (e.g., the shape/profile of the top surface of the perforated plate) may extend along the longitudinal axis and along the lateral axis of the heat exchanger. For example, the perforated plate (e.g., the top surface of the perforated plate) may form an arc along the longitudinal axis and an arc along the lateral axis. Moreover, the shape/profile of the perforated plate (e.g., the shape/profile of the top surface of the perforated plate) along the longitudinal axis may be different than the shape/profile of the perforated plate (e.g., the shape/profile of the top surface of the perforated plate) along the lateral axis. For example, the shape/profile of the perforated plate (e.g., the shape/profile of the top surface of the perforated plate) may be substantially constant along one axis (e.g., the lateral axis) and arcuate along the other axis (e.g., the longitudinal axis). It should be appreciated that the shaped/profiled perforated plate (e.g., the shaped/profiled top surface of the perforated plate) may be utilized on any of the embodiments disclosed herein, or the perforated plate (e.g., the top surface of the perforated plate) may be substantially flat. 
       FIG. 9  is a top view of another embodiment of a perforated plate  97  that may be used in the refrigerant distributor  78  of  FIG. 4 . In the illustrated embodiment, the holes  92  are arranged in five rows, and each row extends along the longitudinal axis  86 . In certain embodiments, each row may be aligned (e.g., substantially aligned) with a respective evaporating tube, such that the center point of each hole is aligned (e.g., substantially aligned) with the centerline of the respective evaporating tube. While the holes  92  are arranged in five rows in the illustrated embodiment, it should be appreciated that the holes may be arranged in more or fewer rows in alternative embodiments. 
     In the illustrated embodiment, the spacings between adjacent holes  92  of each row varies along the longitudinal axis  86 . As illustrated, the spacings between adjacent holes  92  of each row decreases along the longitudinal axis  86  from a central portion  124  to each distal portion  126  of the perforated plate  97 . In the illustrated embodiment, each row includes seven holes  92  between the central portion  124  and each distal portion  126 . However, it should be appreciated that each row may include more or fewer holes in alternative embodiments. As illustrated, a first spacing  128  along the longitudinal axis  86  between a first hole  130  and a second hole  132  is greater than a second spacing  134  along the longitudinal axis  86  between the second hole  132  and a third hole  136 . In addition, the second spacing  134  is greater than a third spacing  138  along the longitudinal axis  86  between the third hole  136  and a fourth hole  140 . Furthermore, the third spacing  138  is greater than a fourth spacing  142  along the longitudinal axis  86  between the fourth hole  140  and a fifth hole  144 . The fourth spacing  142  is greater than a fifth spacing  146  along the longitudinal axis  86  between the fifth hole  144  and a sixth hole  148 . In addition, the fifth spacing  146  is greater than a sixth spacing  150  along the longitudinal axis  86  between the sixth hole  148  and a seventh hole  152 . The decreasing spacing along the longitudinal axis between the central portion and each distal portion may establish a substantially even distribution of refrigerant across the top surface of the perforated plate. For example, refrigerant may be directed toward the central portion of the perforated plate (e.g., via a refrigerant header), and the refrigerant may flow to the distal portions of the perforated plate. As the refrigerant flows from the central portion to the distal portions, a portion of the refrigerant may flow through the holes proximate to the central portion, thereby reducing the quantity of refrigerant that reaches the distal portions. Accordingly, the wider hole spacing proximate to the central portion induces more refrigerant to flow toward the distal portions, as compared to a perforated plate with evenly spaced holes along the longitudinal axis. As a result, the refrigerant may be substantially evenly distributed across the perforated plate. 
     In the illustrated embodiment, the spacing pattern on a first side  154  of a lateral centerline  156  of the perforated plate  97  is symmetrical with the spacing pattern on a second side  158  of the lateral centerline  156 . However, it should be appreciated that the spacing patterns on the sides of the lateral centerline may be asymmetrical in alternative embodiments. Furthermore, while the spacing patterns of the rows are substantially the same as one another in the illustrated embodiment, it should be appreciated that in alternative embodiments, at least one row may have a different spacing pattern. In addition, while the hole spacing decreases between each pair of adjacent holes along the longitudinal axis between the central portion and each distal portion in the illustrated embodiment, it should be appreciated that in alternative embodiments, different spacing pattern(s) may be utilized to control the refrigerant flow across the perforated plate (e.g., based on the longitudinal location(s) at which refrigerant is directed toward the perforated plate). For example, in certain embodiments, the hole spacings between certain pairs of adjacent holes in a row may be substantially equal to one another, and/or the hole spacings between certain pairs of adjacent holes in a row may increase along the longitudinal axis between the central portion and at least one distal portion. It should be appreciated that the variations in hole spacing may be utilized on any of the perforated plate embodiments disclosed herein, or at least a portion of the holes within a perforated plate may have substantially equal spacing along the longitudinal axis. 
       FIG. 10  is a top view of a further embodiment of a perforated plate  99  that may be used in the refrigerant distributor  78  of  FIG. 4 . In the illustrated embodiment, the holes  92  are arranged in five rows, and each row extends along the longitudinal axis  86 . In certain embodiments, each row may be aligned (e.g., substantially aligned) with a respective evaporating tube, such that the center point of each hole is aligned (e.g., substantially aligned) with the centerline of the respective evaporating tube. While the holes  92  are arranged in five rows in the illustrated embodiment, it should be appreciated that the holes may be arranged in more or fewer rows in alternative embodiments. 
     In the illustrated embodiment, the sizes of adjacent holes  92  of each row vary along the longitudinal axis  86 . As illustrated, the sizes of adjacent holes  92  of each row increase along the longitudinal axis  86  from the central portion  124  to each distal portion  126  of the perforated plate  99 . In the illustrated embodiment, each row includes six holes  92  between the central portion  124  and each distal portion  126 . However, it should be appreciated that each row may include more or fewer holes in alternative embodiments. As illustrated, a first size (e.g., first diameter  160 ) of a first hole  162  is less than a second size (e.g., second diameter  164 ) of a second hole  166 . In addition, the second size (e.g., second diameter  164 ) of the second hole  166  is less than a third size (e.g., third diameter  168 ) of a third hole  170 . Furthermore, the third size (e.g., third diameter  168 ) of the third hole  170  is less than a fourth size (e.g., fourth diameter  172 ) of a fourth hole  174 . The fourth size (e.g., fourth diameter  172 ) of the fourth hole  174  is less than a fifth size (e.g., fifth diameter  176 ) of a fifth hole  178 . Furthermore, the fifth size (e.g., fifth diameter  176 ) of the fifth hole  178  is less than a sixth size (e.g., sixth diameter  180 ) of a sixth hole  182 . The increasing sizes of the holes along the longitudinal axis between the central portion and each distal portion may establish a substantially even distribution of refrigerant across the top surface of the perforated plate. For example, refrigerant may be directed toward the central portion of the perforated plate (e.g., via a refrigerant header), and the refrigerant may flow to the distal portions of the perforated plate. As the refrigerant flows from the central portion to the distal portions, a portion of the refrigerant may flow through the holes proximate to the central portion, thereby reducing the quantity of refrigerant that reaches the distal portions. Accordingly, the small holes proximate to the central portion induce more refrigerant to flow toward the distal portions, as compared to a perforated plate with equally sized holes along the longitudinal axis. As a result, the refrigerant may be substantially evenly distributed across the perforated plate. 
     In the illustrated embodiment, the hole size pattern on the first side  154  of the lateral centerline  156  of the perforated plate  99  is symmetrical with the hole size pattern on the second side  158  of the lateral centerline  156 . However, it should be appreciated that the hole size patterns on the sides of the lateral centerline may be asymmetrical in alternative embodiments. Furthermore, while the hole size patterns of the rows are substantially the same as one another in the illustrated embodiment, it should be appreciated that in alternative embodiments, at least one row may have a different hole size pattern. In addition, while the size of each hole increases along the longitudinal axis between the central portion and each distal portion in the illustrated embodiment, it should be appreciated that in alternative embodiments, different hole size pattern(s) may be utilized to control the refrigerant flow across the perforated plate (e.g., based on the longitudinal location(s) at which refrigerant is directed toward the perforated plate). For example, in certain embodiments, the sizes of certain adjacent holes in a row may be substantially equal to one another, and/or the hole size may decrease between certain adjacent holes in a row along the longitudinal axis between the central portion and at least one distal portion. It should be appreciated that the variation in hole sizes may be utilized on any of the perforated plate embodiments disclosed herein (e.g., the variation in hole sizes may be combined with the variation in hole spacing), or at least a portion of the holes within a perforated plate may have substantially equal hole sizes along the longitudinal axis. 
       FIG. 11  is a schematic diagram of a portion of an embodiment of a falling film evaporator  64  that may be used in the HVAC&amp;R system of  FIG. 1 . In the illustrated embodiment, the falling film evaporator  64  includes a spray header  200  positioned above the refrigerant distributor  78  within the shell. The spray header  200  is configured to receive refrigerant (e.g., from the inlet of the shell) and to direct the refrigerant toward the refrigerant distributor  78 . In the illustrated embodiment, the spray header  200  includes an inlet  202  configured to receive the refrigerant, two spray heads  204  configured to output the refrigerant toward the refrigerant distributor  78 , and a manifold  206  configured to direct the refrigerant from the inlet  202  to the spray heads  204 . While the illustrated embodiment include two spray heads, it should be appreciated that in alternative embodiments, the spray header may include more or fewer spray heads (e.g., 1, 2, 3, 4, 5, 6, or more). 
     In the illustrated embodiment, the spray heads  204  extend along the lateral axis  88  substantially perpendicular to the direction of extension of the evaporating tubes  82 . As used herein, substantially perpendicular refers to an angle between the spray heads and the evaporating tubes of about 45 degrees to about 135 degrees, about 60 degrees to about 120 degrees, about 75 degrees to about 105 degrees, about 80 degrees to about 100 degrees, or about 90 degrees. Each spray head includes multiple openings distributed along the lateral extent of the spray head (e.g., such that the openings are arranged along the lateral axis). Each opening is configured to output refrigerant toward the refrigerant distributor. Because the openings in the spray header are arranged along the lateral axis, the refrigerant may be distributed more evenly along the lateral axis than heat exchangers having a spray header with openings arranged along the longitudinal axis. Furthermore, in certain embodiments, the refrigerant distributor may include features configured to substantially evenly distribute the refrigerant along the longitudinal axis, such as a shaped/profiled perforated plate, variations in hole spacing within the perforated plate, variations in hole sizes within the perforated plate, or a combination thereof. It should be appreciated that the spray header described above may be utilized with any of the heat exchanger embodiments disclosed herein. 
     While the embodiments disclosed herein are described with reference to a falling film evaporator, it should be appreciated that certain embodiments disclosed herein (e.g., certain embodiments of the perforated plate) may be employed within other suitable heat exchangers, such as a hybrid falling film heat exchanger (e.g., a falling film heat exchanger with condensing tubes positioned above the perforated plate). Furthermore, while the refrigerant distributors disclosed herein include a single perforated plate, it should be appreciated that in alternative embodiments, the refrigerant distributor may include multiple perforated plates (e.g., an additional perforated plate substantially parallel to the perforated plate disclosed herein). In addition, while the perforated plates disclosed herein include substantially circular holes, it should be appreciated that in alternative embodiments, the holes in the perforated plate may have other suitable shapes, such as elliptical or polygonal, among others. 
     While only certain features and embodiments 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 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 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 disclosure, or those unrelated to enabling the claimed disclosure). 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.