Combination heat exchanger for cascade refrigeration system

Abstract

A cascade refrigeration system (10) includes a high side working fluid assembly (20), a low side working fluid assembly (22), and a combination heat exchanger (70). The combination heat exchanger (70) includes a first section (130) having a low side lubricant separator (148) configured to separate lubricant from a low side working fluid and a low side working fluid receiver (176). The combination heat exchanger (70) further includes a second section (132) having a plurality of heat exchange tubes (163) configured to receive the low side working fluid and direct the low side working fluid therethrough, a high side working fluid inlet (156) configured to receive high side working fluid and place the high side working fluid into a heat exchange relationship with the low side working fluid, and a high side lubricant return vessel (159) configured to receive additional lubricant from the high side working fluid.

Description

COMBINATION HEAT EXCHANGER FOR CASCADE REFRIGERATION SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from and the benefit of U.S. Provisional Application No. 63 / 551,980, entitled “COMBINATION HEAT EXCHANGER FOR CASCADE REFRIGERATION SYSTEM,” filed February 9, 2024, which is herein incorporated by reference in its entirety for all purposes.BACKGROUND

[0002] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0003] Cascade refrigeration systems are becoming increasingly prevalent, namely, in industrial refrigeration applications, to provide adequate cooling for temperature-controlled storage. For example, cascade refrigeration systems generally employ a common heat exchanger shared between a low side (e.g., low pressure side) working fluid assembly and a high side (e.g., high pressure side) working fluid assembly. Each of the low side working fluid assembly and the high side working fluid assembly may employ one or more compressors to circulate a working fluid (e.g., refrigerant) therethrough, thereby enabling the working fluid to change phases between vapor, liquid, and combinations thereof in response to exposure to different temperatures and pressures associated with operation of the respective working fluid assembly. However, traditional cascade refrigeration systems and methods may be susceptible to various inefficiencies. Further, traditional cascade refrigeration systems may employ numerous separate components arranged about a respective working fluid assembly to provide the desired cooling, heating, and / or various other functionalities, thereby increasing a cost associated with the manufacture and assembly of such refrigeration systems.SUMMARY

[0004] A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.

[0005] In an embodiment, a cascade refrigeration system includes a high side working fluid assembly, a low side working fluid assembly, and a combination heat exchanger. The combination heat exchanger includes a first section having a low side lubricant separator configured to separate lubricant from a low side working fluid and a low side working fluid receiver. The combination heat exchanger further includes a second section having a plurality of heat exchange tubes configured to receive the low side working fluid and direct the low side working fluid therethrough, a high side working fluid inlet configured to receive high side working fluid and place the high side working fluid into a heat exchange relationship with the low side working fluid, and a high side lubricant return vessel configured to receive additional lubricant from the high side working fluid.

[0006] In another embodiment, a combination heat exchanger for a cascade refrigeration system includes a first tube sheet and a second tube sheet configured to separate the combination heat exchanger into a first section, a second section, and a third section, a low side lubricant separator positioned within a first chamber of the first section and configured to separate lubricant from a low side working fluid and direct the low side working fluid toward the second section. The combination heat exchanger further includes a high side working fluid inlet fluidly coupled to the second section and configured to direct a high side working fluid into the second section, a plurality of heat exchange tubes extending within the second section and configured to receive the low side working fluid from the low side lubricant separator, transfer heat from the low side working fluid to the high side working fluid directed across the plurality of heat exchange tubes, and discharge the low side working fluid into a second chamber of the first section. The combination heat exchanger further includes a conduit extending within the second section and configured to receive vaporized high side working fluid and direct the vaporized high side workingfluid out of the combination heat exchanger, and a low side working fluid receiver fluidly coupled to the second chamber of the first section and configured to receive the low side working fluid from the plurality of heat exchange tubes.

[0007] In another embodiment, a cascade refrigeration system includes a high side working fluid vapor compression circuit comprising a first compressor configured to circulate a high side working fluid through the high side working fluid vapor compression circuit, a low side working fluid vapor compression circuit comprising a second compressor configured to circulate a low side working fluid through the low side working fluid vapor compression circuit, a combination heat exchanger, and a controller configured to control operation of the combination heat exchanger to satisfy a cooling load on the low side working fluid vapor compression circuit. The combination heat exchanger is configured to receive the low side working fluid via a plurality of tubes, receive the high side working fluid via a high side working fluid inlet, condense the low side working fluid and evaporate the high side working fluid via heat exchange between the low side working fluid and the high side working fluid, and separate lubricant from the low side working fluid and additional lubricant from the high side working fluid.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0009] FIG. 1 is a perspective view of an embodiment of a cascade refrigeration system that may be utilized in an industrial refrigeration application, in accordance with an aspect of the present disclosure;

[0010] FIG. 2 is a schematic view of an embodiment of a cascade refrigeration system having a cascade heat exchanger, in accordance with an aspect of the present disclosure;

[0011] FIG. 3 is a perspective view of an embodiment of a portion of a combination heat exchanger of a cascade refrigeration system, in accordance with an aspect of the present disclosure;

[0012] FIG. 4 is longitudinal cross-sectional view of an embodiment of a combination heat exchanger, in accordance with an aspect of the present disclosure;

[0013] FIG. 5 is a perspective view of an embodiment of a tube sheet employed by a combination heat exchanger, in accordance with an aspect of the present disclosure; and

[0014] FIG. 6 is a lateral cross-sectional view of an embodiment of a section of a combination heat exchanger, in accordance with an aspect of the present disclosure.DETAILED DESCRIPTION

[0015] One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. 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 to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that 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.

[0016] When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0017] As used herein, the terms “approximately,” “generally,” “substantially,” and so forth, are intended to convey that the property value being described may be within a relatively small range of the property value, as those of ordinary skill would understand. For example, when a property value is described as being “approximately” equal to (or, for example, “substantially similar” to) a given value, this is intended to convey that the property value may be within + / - 5%, within + / - 4%, within + / - 3%, within + / - 2%, within + / - 1%, or even closer, of the given value.Similarly, when a given feature is described as being “substantially parallel” to another feature, “generally perpendicular” to another feature, and so forth, this is intended to convey that the given feature is within + / - 5%, within + / - 4%, within + / - 3%, within + / - 2%, within + / - 1%, or even closer, to having the described nature, such as being parallel to another feature, being perpendicular to another feature, and so forth. Mathematical terms, such as “parallel” and “perpendicular,” should not be rigidly interpreted in a strict mathematical sense, but should instead be interpreted as one of ordinary skill in the art would interpret such terms. For example, one of ordinary skill in the art would understand that two lines that are substantially parallel to each other are parallel to a substantial degree, but may have minor deviation from exactly parallel.

[0018] As briefly discussed above, refrigeration systems (e.g., industrial refrigeration systems) may employ cascade refrigeration systems to satisfy cooling demands in temperature-controlled storage. Cascade refrigeration systems may include a high side working fluid assembly (e.g., first chiller system, first vapor compression system, ammonia refrigerant circuit, ammonia working fluid circuit) and a low side working fluid assembly (e.g., second chiller system, second vapor compression system, carbon dioxide refrigerant circuit, carbon dioxide working fluid circuit) that are fluidly separate from one another. Each of the high side working fluid assembly and the low side working fluid assembly may employ a compressor configured to circulate the respective working fluid therethrough, thereby enabling the respective working fluid to change phases between vapor, liquid, and combinations thereof in response to exposure to different temperatures and pressures associated with operation of the respective working fluid assembly. Further, the high side working fluid assembly and the low side working fluid assembly may share a heat exchanger (e.g., cascade heat exchanger, common heat exchanger), thereby enabling the cascade refrigeration system to satisfy industrial refrigeration cooling demands. For example, the shared heat exchanger may operate as an evaporator for the high side working fluid assembly and as a condenser for the low side working fluid assembly, thereby enabling a working fluid (e.g., carbon dioxide) of the low side working fluid assembly to be directly (e.g., via direct heat transfer) condensed by a working fluid (e.g., ammonia) of the high side working fluid assembly.

[0019] In traditional cascade refrigeration systems, numerous separate, ancillary components may be employed to perform various functions. For example, lubricant separator vessels may be employed to separate lubricant (e.g., oil) from a respective working fluid stream, lubricant potvessels may be employed to collect and / or redistribute lubricant (e.g., oil) to components of the cascade refrigeration system, surge drum vessels may be employed to separate vaporous and liquid ammonia, CO2 receiver vessels may be employed to collect liquid and / or vaporous carbon dioxide, ammonium carbamate isolation systems may be employed to isolate compounds formed via mixing of respective working fluids, and so forth. Each of the above-described components (e.g., lubricant separator vessels, lubricant pot vessels, surge drum vessels, CO2 receiver vessels, and ammonium carbamate isolation systems) may be configured and / or positioned along a vapor compression circuit (e.g., along a high side working fluid assembly of a vapor compression circuit, along a low side working fluid assembly of a vapor compression circuit) as a separate, discrete component to enable the cascade refrigeration system to provide the desired functionality (e.g., cooling temperature-controlled storage devices). However, by employing separate, ancillary components, costs associated with manufacture, transportation, assembly, and maintenance of traditional cascade systems may be increased. It is now recognized that improved cascade refrigeration systems are desired.

[0020] Accordingly, the present disclosure is directed to a cascade heat exchanger (e.g., combination cascade heat exchanger) that may be employed by a cascade refrigeration system. The cascade heat exchanger may be separated into various sections, portions, and / or compartments, thereby enabling the cascade heat exchanger to integrate one or more of the ancillary components discussed above into a single heat exchanger (e g., heat exchanger assembly) as one (e.g., a single) component. For example, the combination cascade heat exchangers discussed herein may include a section configured to separate vaporous ammonia from liquid ammonia, thereby serving as a surge drum vessel. Additionally, the combination cascade heat exchangers may include a lubricant processing system (e.g., lubricant processing assembly) and a carbon dioxide receiver vessel, thereby serving as the lubricant pot and lubricant separator vessels and the carbon dioxide receiver vessels, respectively. Further still, the combination cascade heat exchangers discussed herein may include a specialized tube sheet configured to detect the presence of ammonium carbamate, thereby serving as an ammonium carbamate isolation system. By including one or more of the above described components into a single combination cascade heat exchanger, costs associated with the manufacture, transportation, assembly, and maintenance of cascade refrigeration systems employing a combination cascade heat exchanger may be reduced. For example, the reduction in space and weight by virtue of employing fewer separate componentsmay enable an industrial CO2 / NH3 cascade refrigeration system to be assembled in a compact package that may be more readily and easily transported as a single unit. Further, the service and manufacturing simplicity of a single, compact package enables the system to be standardized and automated, thereby further increasing savings associated with the manufacture and assembly of such refrigeration systems.

[0021] Turning now to the drawings, FIG. 1 is a perspective view of an embodiment of a cascade refrigeration system 10 that may be employed in industrial refrigeration applications to satisfy large cooling demands. As used herein, a cascade refrigeration system includes any number of components configured to enable regulation of parameters related to climate characteristics, such as temperature, humidity, air flow, pressure, air quality, and so forth. Components or parts of a cascade refrigeration system may include, but are not limited to, all, some of, or individual parts, such as a heat exchanger, an air flow control device, such as a fan, a sensor configured to detect a climate characteristic or operating parameter, a receiver, a separator, a lubricant system, a component configured to enable regulation of climate characteristics, or a combination thereof. The embodiments described herein may be utilized in a variety of applications to control climate characteristics, such as commercial, industrial, transportation, residential, or other applications where climate control is desired.

[0022] In certain embodiments, the cascade refrigeration system 10 may be positioned proximate (e.g., within a threshold distance of) a building (e.g., temperature-controlled storage space) and may be configured to satisfy industrial refrigeration cooling demands associated with operation of the building. In the illustrated embodiment, the cascade refrigeration system 10 is a single package unit that may include multiple independent refrigeration circuits and components that are tested, charged, wired, piped, and ready for installation, thereby reducing costs associated with manufacture, transportation, and assembly of the cascade refrigeration system 10.

[0023] As shown in the illustrated embodiment of FIG. 1, a housing 12 encloses the cascade refrigeration system 10 and provides structural support and protection to the internal components from environmental and other contaminants. For example, the housing 12 may include multiple sides 14 that collectively define an interior volume 16 of the cascade refrigeration system 10. Each of the sides 14 may receive and / or be at least partially defined by one or more panels 18 (e.g.,partition walls) that may be removably coupled to the sides 14, thereby enabling an operator to service components of the cascade refrigeration system 10 disposed within the interior volume 16.

[0024] For example, the cascade refrigeration system 10 may include a high side working fluid assembly 20 (e.g., first vapor compression circuit, first working fluid circuit, NH3 working fluid assembly) and a low side working fluid assembly 22 (e.g., second vapor compression circuit, second working fluid circuit, CO2 working fluid assembly) disposed within the interior volume 16. Each of the high side working fluid assembly 20 and the low side working fluid assembly 22 may include one or more heat exchangers 24 in fluid communication with the working fluid assemblies 20, 22. Tubes within the heat exchangers 24 may circulate working fluid, such as ammonia and / or carbon dioxide, through the heat exchangers 24. The tubes may be of various types, such as multichannel tubes, copper or aluminum tubing, and so forth. Together, the heat exchangers 24 of the high side working fluid assembly 20 and the low side working fluid assembly 22 may implement a thermal cycle in which the respective working fluids directed through the working fluid assemblies 20, 22 undergo phase changes and / or temperature changes as the working fluid flows through the heat exchangers 24. For example, as discussed in greater detail below, the high side working fluid assembly 20 and the low side working fluid assembly 22 may share at least one of the heat exchangers 24, thereby enabling the working fluid (e.g., ammonia) of the high side working fluid assembly 20 to directly condense a working fluid (e.g., carbon dioxide) of the low side working fluid assembly 22 within the shared heat exchanger 24 of the cascade refrigeration system 10. It should be appreciated that, while other working fluids may be used in accordance with the present techniques, the present disclosure refers to the high side working fluid as ammonia and the low side working fluid as carbon dioxide.

[0025] Additionally, the cascade refrigeration system 10 may include other equipment and / or components for implementing the thermal cycle. For example, one or more compressors 26 may be utilized by each of the high side working fluid assembly 20 and the low side working fluid assembly 22 to increase the pressure and temperature of the respective working fluid directed therethrough before the working fluid enters a heat exchanger 24. The compressors 26 may be any suitable type of compressor, such as scroll compressors, rotary compressors, screw compressors, or reciprocating compressors. Additional equipment and devices may be included in the cascade refrigeration system 10, such as expansion valves, conduits, vessels, separators, andthe like, thereby enabling the high side working fluid assembly 20 and the low side working fluid assembly 22 to circulate a respective working fluid (e.g., ammonia, carbon dioxide) therethrough.

[0026] FIG. 2 is a schematic view of an embodiment of the cascade refrigeration system 10 including the high side working fluid assembly 20 and the low side working fluid assembly 22 configured to satisfy a cooling load 30 (e.g., cooling demand) associated with a temperature- controlled building, room, space, storage device, and the like. In the illustrated embodiment, the high side working fluid assembly 20 may circulate a working fluid (e.g., ammonia) through the high side working fluid assembly 20 starting with a compressor 50 (e.g., high side compressor, ammonia compressor), which may correspond to one of the compressors 26 described above. The high side working fluid assembly 20 may also include a condenser 52 (e.g., ammonia condenser) and an expansion valve(s) or device(s) 54. Similarly, the low side working fluid assembly 22 may circulate a working fluid (e.g., carbon dioxide) through the low side working fluid assembly 22 starting with a compressor 60 (e.g., low side compressor, carbon dioxide compressor), which may correspond to one of the compressors 26 describe above. The low side working fluid assembly 22 may include an evaporator 62 (e.g., CO2 evaporator) and an expansion valve(s) or device(s) 64. Notably, the high side working fluid assembly 20 and the low side working fluid assembly 22 share a combination heat exchanger 70 (e.g., cascade heat exchanger, shared heat exchanger, common heat exchanger, ammonia evaporator, carbon dioxide condenser), such that the combination heat exchanger 70 functions as an evaporator for the high side working fluid assembly 20 and as a condenser for the low side working fluid assembly 22.

[0027] For example, the compressor 50 of the high side working fluid assembly 20 may be configured to receive high side vaporous working fluid (e.g., low pressure ammonia vapor) from the combination heat exchanger 70, pressurize the high side vaporous working fluid, and discharge the high side vaporous working fluid (e.g., high pressure ammonia vapor) toward the condenser 52. The condenser 52 may be configured to decrease a temperature of the high side vaporous working fluid, thereby enabling high side vaporous working fluid to condense into high side liquid working fluid. For example, the high side working fluid may be directed through tubes of the condenser 52, and a cooling fluid (e.g., water, air) may be directed across the tubes of the condenser 52. The cooling fluid may be at a lower temperature than the high side working fluid, thereby enabling transfer of heat from the high side working fluid to the cooling fluid. As the high sideworking fluid transfers heat to the cooling fluid, the high side vaporous working fluid may change phases and condense to a high side liquid working fluid. The high side liquid working fluid may then be directed through the expansion valve 54, thereby further decreasing a pressure and temperature of the high side working fluid before the high side working fluid is directed into the combination heat exchanger 70 to exchange heat with the low side working fluid from the low side working fluid assembly 22, as discussed below.

[0028] The compressor 60 of the low side working fluid assembly 22 may be configured to receive low side vaporous working fluid (e.g., low pressure carbon dioxide vapor) from the evaporator 62, pressurize the low side vaporous working fluid, and discharge the low side vaporous working fluid (e.g., high pressure carbon dioxide) toward the combination heat exchanger 70. The combination heat exchanger 70 may be configured to decrease a temperature of the low side vaporous working fluid, thereby enabling the low side vaporous working fluid to condense into a low side liquid working fluid. For example, the low side working fluid may be directed through tubes of the combination heat exchanger 70 and may exchange heat with a conditioning fluid (e.g., high side working fluid) directed across the tubes of the combination heat exchanger. In certain embodiments, the conditioning fluid utilized to cool and condense the low side working fluid may correspond to the high side working fluid of the high side working fluid assembly 20. For example, as noted above, after the high side working fluid is cooled by the condenser 52, the high side working fluid is directed through the expansion valve 54 and is discharged into the combination heat exchanger 70.

[0029] The low side working fluid directed through the tubes of the combination heat exchanger 70 may be at a higher temperature than the high side working fluid directed over (e.g., across the tubes of the combination heat exchanger 70. Thus, the low side working fluid may transfer heat (e.g., through the tubes) to the high side working fluid. For example, the low side working fluid may deposit heat to the high side working fluid, thereby causing the high side working fluid to increase in temperature and vaporize. The high side vaporous working fluid may then be collected and directed toward a suction side of the compressor 50, thereby enabling the high side working fluid to repeat the cycle through the high side working fluid assembly 20. Further, as the low side working fluid deposits heat to the high side working fluid, the vaporous low side working fluid may decrease in temperature, thereby causing the low side working fluidto condense into a low side liquid working fluid within the tubes of the combination heat exchanger 70. Thus, the combination heat exchanger 70 may function as an evaporator for the high side working fluid of the high side working fluid assembly 20 and as a condenser for the low side working fluid of the low side working fluid assembly 22.

[0030] Upon transferring heat to the high side working fluid, the low side liquid working fluid may be directed out of the combination heat exchanger 70 and toward the expansion valve 64. The expansion valve 64 may be configured to further decrease a pressure, and thus, a temperature of the low side working fluid before directing the low side working fluid toward the evaporator 62. In the evaporator 62, the low side working fluid may exchange heat with a conditioning fluid (e.g., glycol, water, air), and the conditioning fluid may be circulated through the cooling load 30 to satisfy cooling demands associated with a building, space, or device employing the cascade refrigeration system 10. For example, low side working fluid entering the evaporator 62 from the expansion valve 64 may be at a lower temperature relative to the conditioning fluid directed through the evaporator 62. As such, as the conditioning fluid is directed through the evaporator 62, the conditioning fluid may transfer heat to the low side working fluid, thereby causing the conditioning fluid to decrease in temperature and the low side working fluid to increase in temperature. Upon decreasing the temperature of the conditioning fluid to a desired temperature (e g., based on a cooling demand associated with the cooling load 30), the conditioning fluid may be directed toward the cooling load 30, thereby enabling the conditioning fluid to satisfy a cooling demand associated with the cooling load 30. Further, as the temperature of the low side working fluid increases, the low side working fluid may vaporize. The low side vaporous working fluid may then be directed toward a suction side of the compressor 60, thereby enabling the low side working fluid to repeat the cycle through the low side working fluid assembly 22.

[0031] In certain embodiments, lubricant may be circulated throughout the cascade refrigeration system 10 to enable efficient operation of certain components of the cascade refrigeration system 10 (e.g., enable efficient operation of the compressors 50, 60). For example, lubricant (e.g., oil) may be directed into each of the compressors 50, 60 to lubricate components thereof (e.g., bearings, actuators, displacement components, and the like), thereby enabling efficient operation of the compressors 50, 60. At times, lubricant may mix with a respective working fluid directed through the compressors 50, 60 such that a lubricant working fluid mixtureis discharged from the respective compressor 50, 60. Accordingly, the cascade refrigeration system 10 may employ a high side lubricant return assembly 51 and a low side lubricant return assembly 61, each configured to return lubricant from a respective working fluid / lubricant mixture to a corresponding compressor 50, 60.

[0032] For example, the compressor 50 of the high side working fluid assembly 20 may discharge a high side working fluid / lubricant mixture (e.g., ammonia and lubricant mixture) from the compressor 50 toward the condenser 52. The high side working fluid / lubricant mixture may pass through the condenser 52 of the high side working fluid assembly 20 before being directed through the expansion valve 54 and toward the combination heat exchanger 70. As the high side working fluid / lubricant mixture exchanges heat with the low side working fluid (e.g., as the high side working fluid receives heat from the low side working fluid) within the combination heat exchanger 70, the high side working fluid may evaporate, thereby enabling lubricant within the high side working fluid to separate from the vaporous high side working fluid. The lubricant from the high side working fluid / lubricant mixture may fall via gravity toward a bottom portion of the combination heat exchanger 70, thereby enabling the lubricant from the high side working fluid / lubricant mixture to be collected by a lubricant collection vessel within the combination heat exchanger 70, as described in greater detail below. The lubricant for the high side working fluid assembly 20 may then be returned to the compressor 50 via the high side lubricant return assembly 51 . In certain embodiments, the high side lubricant return assembly 51 may include pumps, valves, and / or other components configured to enable the high side lubricant return assembly 51 to circulate lubricant throughout the high side working fluid assembly 20.

[0033] In certain embodiments, the compressor 60 of the low side working fluid assembly 22 may discharge a low side working fluid / lubricant mixture (e.g., carbon dioxide and lubricant mixture) from the compressor 60 toward the combination heat exchanger 70. The low side working fluid / lubricant mixture may be directed through a portion of the combination heat exchanger 70 that includes a lubricant separator configured to separate and / or remove lubricant from the low side working fluid, as described in greater detail below. Thus, the low side working fluid / lubricant mixture may be directed through the lubricant separator such that tubes of the combination heat exchanger 70 receive low side working fluid that contains less than a threshold amount of lubricant (e.g., less than 1 percent lubricant). The lubricant separator may be fluidlycoupled to the low side lubricant return assembly 61 , thereby enabling the low side lubricant return assembly 61 to recirculate lubricant toward the compressor 60. In certain embodiments, the low side lubricant return assembly 61 may include pumps, valves, and / or other components configured to enable the low side lubricant return assembly 61 to circulate lubricant throughout the low side working fluid assembly 22.

[0034] Additionally, the cascade refrigeration system 10 may include additional components that enable the cascade refrigeration system 10 to satisfy cooling demands associated with the cooling load 30. For example, the low side working fluid assembly 22 may include a filter drier 80 configured to decrease an amount of moisture in the low side working fluid flow directed toward the evaporator 62, a suction superheater 82 configured to further increase a temperature of the low side working fluid exiting the evaporator 62, valves 84 configured to control a flow direction of the low side working fluid through components of the low side working fluid assembly 22, and an lubricant rectifier 86 configured to further separate lubricant from low side working fluid. For example, the lubricant rectifier 86 may correspond to a shell and tube heat exchanger in which high-pressure liquid is routed through the shell side and saturated low side working fluid / lubricant mixture is routed through the tube side. The heat from the high-pressure liquid evaporates working fluid from the saturated low side working fluid / lubricant mixture within the tubes of the lubricant rectifier 86 which separates lubricant from the low side working fluid. The evaporated low side working fluid may then be directed through the evaporator 62 to continue through the low side working fluid assembly 22.

[0035] In certain embodiments, one or more sensors 90 may also be distributed throughout the cascade refrigeration system 10. The one or more sensors 90 may be configured to collect data indicative of an operating parameter of the cascade refrigeration system 10, including a pressure and / or temperature of a respective working fluid directed through the cascade refrigeration system 10, a chemical composition of a respective working fluid and lubricant mixture (e.g., an amount of lubricant present within a working fluid flow), a humidity level associated with a respective working fluid, or any combination thereof. In certain embodiments, such data may be communicated to a controller 100, thereby enabling the controller 100 to control various aspects of the cascade refrigeration system 10 to satisfy a cooling demand associated with the cooling load 30. Further, it should be appreciated that the sensors 90 may be configured to collect any additionaldata related to operation of the cascade refrigeration system 10 that may enable efficient operation of the cascade refrigeration system 10.

[0036] The one or more sensors 90 may communicate collected data to the controller 100 (e.g., control system, automation controller), thereby enabling the controller 100 to control operation of the cascade refrigeration system 10 to satisfy cooling demands associated with the cooling load 30. In certain embodiments, the controller 100 may include processing circuitry 102 (e.g., one or more microprocessors) and a memory 104. For example, the controller 100 may include non- transitory code or instructions stored in a machine-readable medium (e.g., the memory 104) that is used by the processing circuitry 102 to implement the techniques described herein. The memory 104 may include volatile memory, such as read-only memory (ROM), optical drives, hard disc drives, solid-state drives, or any other non-transitory, computer-readable medium storing instructions that, when executed by the processing circuitry 102, control operation of the cascade refrigeration system 10.

[0037] In certain embodiments, the controller 100 may be communicatively coupled to a thermostat or other control device that may receive an input from an operator indicative of a desired temperature setpoint for the cooling load 30. Upon receiving an indication that the current temperature (e.g., as detected by the one or more sensors 90) deviates from the desired temperature (e.g., as indicated by the user input) by a threshold amount, the controller 100 may operate to control the cascade refrigeration system 10 to satisfy the cooling load 30. For example, the controller 100 may control a speed of the compressors 50, 60 of the high side and low side working fluid assemblies 20, 22, respectively, control a position of the expansion valves 54, 64, and / or control operation of the heat exchangers employed by the cascade refrigeration system 10 (e.g., control operation of the condenser 52 of the high side working fluid assembly 20, control operation of the evaporator 62 of the low side working fluid assembly, control operation of the combination heat exchanger 70 shared between the high side working fluid assembly 20 and the low side working fluid assembly 22).

[0038] As noted above, traditional cascade refrigeration systems may employ numerous ancillary components to facilitate operation of the cascade refrigeration system. For example, traditional cascade refrigeration systems may employ surge drum vessels to separate high sideliquid working fluid from high side vaporous working fluid, lubricant pot vessels and lubricant separator vessels to separate lubricant from a respective high side or low side working fluid flow, carbon dioxide receiver vessels to separate low side liquid working fluid from low side vaporous working fluid, and ammonium carbamate isolation systems to isolate compounds formed from mixing high side working fluid and low side working fluid. In such traditional systems, each of the aforementioned systems and / or vessels may be separate, ancillary components that are assembled (e.g., at an installation or customer site) and disposed along the high side working fluid assembly and / or the low side working fluid assembly to enable operation of the cascade refrigeration system. However, by employing numerous separate components, costs associated with the manufacture, transportation, and assembly of traditional cascade refrigeration systems may be increased.

[0039] To address the shortcomings of traditional cascade refrigeration systems, the combination heat exchanger 70 of the cascade refrigeration system 10 may be configured to provide a number of additional functionalities that have been traditionally provided by separate ancillary components of traditional cascade refrigeration systems. For example, in addition to functioning as the high side working fluid evaporator and the low side working fluid condenser, the combination heat exchanger 70 may include a section or portion that is configured to operate as a surge drum vessel for the high side working fluid. Additionally, the combination heat exchanger 70 may include a section or portion that is configured to operate as a lubricant pot vessel and / or a lubricant separator vessel. The combination heat exchanger 70 may also include a section or portion that is configured to operate as a low side working fluid receiver. Further still, the combination heat exchanger 70 may include and a tube sheet that is configured to operate as an ammonia carbamate isolation system. By integrating each of the systems and / or components discussed above into the combination heat exchanger 70, costs associated with the manufacture, transportation, and assembly of the cascade refrigeration system 10 may be reduced, as discussed in greater detail below.

[0040] With the preceding in mind, FIG. 3 is a perspective view of an embodiment of the combination heat exchanger 70 that may be employed in cascade refrigeration systems, such as the cascade refrigeration system 10 of FIGS. 1 and 2. In the illustrated embodiment, the combination heat exchanger 70 (e.g., cascade heat exchanger) is oriented along a longitudinal axis110, a lateral axis 112, and a vertical axis 1 14 and includes a housing 120 (e.g., shell) with multiple components disposed therein. For example, the housing 120 may extend from a first end 122 to a second end 124 and may define an interior volume 126 of the combination heat exchanger 70. In the illustrated embodiment, certain portions of the housing 120 are shown in phantom lines to facilitate view of the components disposed within the interior volume 126. The interior volume 126 may be separated into various sections via one or more tube sheets 128 (e.g., specialized tube sheet, doubletube sheet). For example, afirst section 130 (e.g., first end, receiving and discharging section, low side lubricant section) may be separated from a second section 132 (e.g., middle section, heat exchange section, high side separator section, high side lubricant section) via a first tube sheet 128, and the second section 132 may be separated from a third section 134 (e.g., free section, venting section) via a second tube sheet 128. The tube sheets 128 may be configured to support one or more tubes of the combination heat exchanger 70, and in certain embodiments, the tube sheets 128 may be configured to detect and / or reduce a risk of low side working fluid leaking into high side working fluid to form undesirable compounds (e.g., ammonium carbamate), as described in greater detail below. In this way, the tube sheets 128 may individually and / or collectively serve as ammonium carbamate isolation systems, thereby decreasing costs associated with the manufacture, transportation, and assembly of cascade refrigeration systems employing the tube sheets 128.

[0041] Each of the sections 130, 132, 134 may be further separated into various portions and / or chambers, and each of the portions and / or chambers may include additional components providing various functionalities to enable the combination heat exchanger 70 to operate efficiently to satisfy a cooling demand (e.g., cooling load 30). For example, the first section 130 may be divided into a first chamber 140 (e.g., low side working fluid receiving chamber, low side working fluid lubricant separator chamber) and a second chamber 142 (e.g., low side working fluid discharge chamber, low side working fluid liquid / vapor separator chamber) via a partition plate 144 (e.g., perforated partition plate). In the illustrated embodiment, a low side working fluid inlet 146 is fluidly coupled to the first chamber 140 and configured to discharge a low side working fluid flow (e.g., vaporous low side working fluid) into the first chamber 140. As noted above, in certain embodiments, the low side working fluid flow entering the combination heat exchanger 70 may include lubricant mixed therewith. Accordingly, the first chamber 140 further includes a low side lubricant separator 148 configured to receive the low side working fluid / lubricant mixture andseparate lubricant from the low side working fluid flow. The lubricant separated from the low side working fluid flow may be directed out of the first chamber 140 via a lubricant return conduit 149, which may be a component of the low side lubricant return assembly 61. The low side working fluid that passes through the low side lubricant separator 148 may be directed into the second section 132 (e.g., directed into heat exchange tubes of the second section 132), thereby enabling the low side working fluid to undergo a heat exchange relationship with high side working fluid directed across the tubes, as described in greater detail below.

[0042] The second section 132 may be divided into a first portion 150 (e g., surge drum vessel portion), a second portion 152 (e.g., tube portion), and a third portion 154 (e.g., high side lubricant return portion). In certain embodiments, the first portion 150 may correspond to and / or be disposed within an upper half of the combination heat exchanger 70 that generally extends along the longitudinal axis 110. For example, the first portion 150 may correspond to a portion that is positioned above a central axis 115 of the combination heat exchanger 70. The second portion 152 and the third portion 154 may correspond to and / or be disposed within a lower half of the combination heat exchanger 70 that generally extends along the longitudinal axis 110 below the central axis 115 of the combination heat exchanger 70.

[0043] In the illustrated embodiment, the first portion 150 of the second section 132 includes an inlet 156 (e.g., high side working fluid inlet) configured to receive high side working fluid (e.g., high side working fluid liquid) and discharge the high side working fluid into the interior volume 126 (e.g., into the first and second portion 150, 152 of the second section 132, over and / or across heat exchange tubes positioned within the second portion 152) of the combination heat exchanger 70. The first portion 150 may also include a conduit 158 (e.g., perforated conduit) extending in a direction (e.g., horizontal direction) along the longitudinal axis 110 proximate a top side of the combination heat exchanger 70. The conduit 158 may be a perforated conduit configured to receive vaporous high side working fluid within the interior volume 126 of the combination heat exchanger 70 and direct the vaporous high side working fluid toward the high side working fluid assembly 20. For example, the conduit 158 may include multiple passages (e.g., perforations, apertures) that enable vaporous working fluid that has been vaporized via the heat exchange relationship with the low side working fluid directed through the tubes of the combination heat exchanger 70 to be entrained into the conduit 158, as described in greater detail below.Additionally, the conduit 158 may be coupled to multiple ports 160 that are fluidly coupled to the high side working fluid assembly 20 (e.g., fluidly coupled to a suction side of the compressor 50), thereby enabling vaporous high side working fluid collected by the conduit 158 to be directed toward the compressor 50 via the ports 160. By separating the vaporous high side working fluid from the liquid high side working fluid within the combination heat exchanger 70, the first portion 150 of the second section 132 may function as a surge drum vessel, thereby decreasing costs associated with the manufacture, transportation, and assembly of cascade refrigeration systems employing the combination heat exchanger 70.

[0044] The second portion 152 of the second section 132 may include a tube support assembly 161 having a body 162 extending through the second section 132. For example, the body 162 may extend through the second section 132 for a length in a first direction (e g., horizontal direction) along the longitudinal axis 110, and may extend through the second section 132 for a height in a second direction (e.g., vertical direction) along the vertical axis 114. Notably, the body 162 of the tube support assembly 161 may extend through the second section 132 below the central axis 115 of the combination heat exchanger 70 (e.g., extend within the bottom half of the second section 132, extend within the second portion 152 of the second section 132). The tube support assembly 161 may be configured to support a plurality of heat exchange tubes 163, and each of the tubes 163 may be configured to direct low side working fluid therethrough, thereby enabling the low side working fluid to be directly condensed by the high side working fluid directed across the heat exchange tubes 163. For example, the tube support assembly 161 may include multiple tube supports 164 (e.g., support plates) coupled to the body 162 and extending from the body 162 in a direction (e.g., horizontal direction) along the lateral axis 112. The tube supports 164 may also extend for a height in a direction (e.g., vertical direction) along the vertical axis 114. Each of the tube supports 164 may include multiple passages (e.g., holes, ports) configured to receive and support the plurality of heat exchange tubes 163 extending through the second portion 152 of the second section 132 along the longitudinal axis 110. Each of the passages of a respective tube support 164 is configured to receive and support a corresponding heat exchange tube 163 of the combination heat exchanger 70 extending through the second section 132 (e.g., extending through the second portion 152 of the second section 132). As such, certain passages and / or ports of the tube supports 164 may align with one another along the longitudinal axis 110 in an assembledconfiguration of the combination heat exchanger 70, thereby enabling the tube supports 164 to collectively support the heat exchange tubes 163.

[0045] In certain embodiments, the heat exchange tubes 163 of the combination heat exchanger 70 may extend for multiple passes through the combination heat exchanger 70 to facilitate adequate heat exchange between the low side working fluid directed through an interior of the tubes 163 and the high side working fluid directed across an exterior of the tubes 163. For example, a first pass 165 of the tubes 163 may extend in a direction (e.g., horizontal direction) along the longitudinal axis 110 from the first section 130 to the third section 134, and a second pass 166 of the tubes may extend in a direction (e.g., horizontal direction) along the longitudinal axis 110 from the third section 134 to the first section 130. In certain embodiments, the first pass 165 may be positioned above the second pass 166 relative to gravity. Further, in certain embodiments, the tube supports 164 of the tube support assembly 161 may at least partially define the first pass 165 and the second pass 166 of the tubes 163, thereby enabling low side working fluid to flow in a first flow direction 167 through the first pass 165 and a second flow direction 168 through the second pass 166, as described in greater detail below. In certain embodiments, a majority portion (e.g., greater than 50 percent) of the low side working fluid within the first pass 165 may correspond to a vaporous low side working fluid, while a majority portion (e.g., greater than 50 percent) of the low side working fluid within the second pass 166 may correspond to a liquid low side working fluid. For example, as the low side working fluid is directed through the first and second passes 165, 166, the low side working fluid may progressively transition from a low side working fluid vapor to a low side working fluid liquid (e.g., as a result of being condensed by the high side working fluid directed across the tubes 163). Further, it should be appreciated that the number of tubes 163 shown in the illustrated embodiment is merely provided for illustrative purposes, and the combination heat exchanger 70 may include any number of additional tubes 163 to facilitate the heat exchange relationship between the high side working fluid and the low side working fluid, as described in greater detail below.

[0046] The third portion 154 of the second section 132 may be separated from the second portion 152 by a tube partition plate 169 (e.g., perforated plate). In certain embodiments, the tube partition plate 169 may align with the partition plate 144 that separates the first section 130 into the first chamber 140 and the second chamber 142. Thus, in certain embodiments, the tubepartition plate 169 and the partition plate 144 may correspond to a single component that extends through the first section 130 and the second section 132. The third portion 154 of the second section 132 may include a high side lubricant return vessel 159 positioned at a lowermost point of the third portion 154 relative to the vertical axis 114. For example, lubricant separated from the high side working fluid flow (e.g., via the heat exchange relationship with the low side working fluid flow through the tubes of the combination heat exchanger 70) may fall through the first portion 150 and the second portion 152 of the second section 132 toward the tube partition plate 169. The tube partition plate 169 may include multiple passages formed therein that enable the lubricant falling through the first and second portions 150, 152 to pass through the tube partition plate 169 and collect within the third portion 154 of the second section 132. The third portion 154 may then direct the lubricant toward the high side lubricant return vessel 159, thereby enabling lubricant to be returned to the compressor 50 (e.g., via the high side lubricant return assembly 51). For example, a base of the third portion 154 may have a compound slope configured to direct lubricant collected within the third portion 154 toward the high side lubricant return vessel 159. By integrating the high side lubricant return vessel 159 into the combination heat exchanger 70, fewer separate, ancillary components may be employed to operate a cascade refrigeration system, thereby reducing costs associated with the manufacture, transportation, and assembly of such cascade refrigeration systems.

[0047] The third section 134 may be disposed proximate the second end 124 of the combination heat exchanger 70 and may define a chamber 170. In certain embodiments, the chamber 170 may house various portions (e.g., tube bends) of the tubes 163 that connect the first pass 165 of the tubes 163 to the second pass 166 of the tubes 163. Additionally, the chamber 170 may be fluidly coupled to one or more vents 172, each configured to release various fluids as needed to enable efficient operation of the combination heat exchanger 70. Returning to the first section 130, the second chamber 142 of the first section 130 may include a basin 174 (e.g., reservoir) fluidly coupled to a low side working fluid receiver 176. The low side working fluid receiver 176 may be configured to receive low side working fluid discharged via the heat exchange tubes 163 disposed within the second section 132. The low side working fluid may be condensed via the heat exchange relationship with the high side working fluid within the second section 132 such that liquid low side working fluid is discharged into the basin 174. However, because a volume of the basin 174 is significantly greater than a volume within the heat exchange tubes 163,as the low side working fluid is directed into the basin 174, the increase in volume may result in a pressure drop, thereby enabling a portion of the low side working fluid to change phases (e.g., vaporize) within the basin 174 and / or low side working fluid receiver 176. The vaporous low side working fluid may be directed through the partition plate 144 (e.g., via passages formed therein) and into the first chamber 140, thereby enabling the vaporous low side working fluid to be recirculated through the tubes 163 of the combination heat exchanger 70, as described in greater detail below. Meanwhile, liquid low side working fluid with the basin 174 may be directed through the low side working fluid receiver 176 and toward the expansion valve 64 and the evaporator 62 to complete the cycle through the low side working fluid assembly 22. By integrating the low side working fluid receiver 176 into the combination heat exchanger 70, fewer separate, ancillary components may be employed to operate a cascade refrigeration system, thereby reducing costs associated with the manufacture, transportation, and assembly of such cascade refrigeration systems.

[0048] Having discussed above various components disposed within and / or employed by the sections 130, 132, 134 of the combination heat exchanger 70, respective working fluid flows through the various sections and / or components of the combination heat exchanger 70 may now be discussed. For example, as noted above, low side working fluid (e.g., vaporous low side working fluid) may be discharged into the first section 130 (e.g., into the first chamber 140 of the first section 130) via the low side working fluid inlet 146. In certain embodiments, the low side working fluid flow may include lubricant mixed therein, and thus, the low side working fluid flow may be directed through the low side lubricant separator 148 configured to separate lubricant from the low side working fluid flow. The separated lubricant may be discharged from the combination heat exchanger 70 and directed into the low side lubricant return assembly 61 via the lubricant return conduit 149. In certain embodiments, the low side lubricant separator 148 may also include a low side working fluid discharge port or manifold fluidly coupled to the heat exchange tubes 163 extending through the second section 132 of the combination heat exchanger 70. Thus, vaporous low side working fluid that has passed through the low side lubricant separator 148 may be directed through the low side working fluid discharge port of the low side lubricant separator 148 and into the heat exchange tubes 163 to exchange heat with the high side working fluid.

[0049] For example, each of the heat exchange tubes 163 extending along the first pass 165 may include an inlet fluidly coupled to the working fluid discharge port or manifold of the low side lubricant separator 148. Thus, the low side working fluid may flow in the first flow direction 167 through the first pass 165 of the heat exchange tubes 163. Upon reaching an end of the first pass 165 (e.g., upon reaching the third section 134), the tubes 163 of the heat exchanger may turn (e.g., via a U-turn or bend in the tubes 163), such that low side working fluid may be directed through the second pass 166 of the tubes in the flow direction 168. The heat exchange tubes 163 extending along the second pass 166 may include an outlet fluidly coupled to the basin 174 of the second chamber 142 of the first section 130, thereby enabling low side working fluid to be discharged from the tubes 163 and into the basin 174 of the second chamber 142 of the first section 130. From the basin 174, the low side working fluid may be directed into the low side working fluid receiver 176 (e.g., via a compound slope along a base of the basin 174). It should be appreciated that as the low side working fluid is directed through the tubes 163 of the combination heat exchanger 70, the low side working fluid may change phases (e.g., transition from vaporous low side working fluid to liquid low side working fluid) via the heat exchange relationship with the high side working fluid directed across the tubes 163 of the combination heat exchanger 70. Thus, the low side working fluid discharged via the second pass 166 of the tubes 163 and toward the low side working fluid receiver 176 may be substantially liquid low side working fluid that has been directly condensed by the high side working fluid of the high side working fluid assembly 20.

[0050] For example, as low side working fluid is directed through the tubes 163, high side working fluid may be discharged into the first portion 150 of the second section 132 via the inlet 156. Because the inlet 156 receives the high side working fluid after the high side working fluid is directed through the condenser 52 and the expansion valve 54, the high side working fluid may be substantially low-pressure, liquid high side working fluid. Further, the liquid high side working fluid discharged into the first portion 150 via the inlet 156 may be cooler than the low side working fluid directed through the tubes 163. For example, in certain embodiments, the controller 100 may be configured to operate the cascade refrigeration system 10 such that high side working fluid discharged into the combination heat exchanger 70 has a temperature that is less than a temperature of the low side working fluid directed through the tubes 163 by a threshold amount, therebyenabling sufficient heat exchange to take place between the high side working fluid and the low side working fluid.

[0051] As the high side working fluid is discharged into the first portion 150 of the second section 132, the high side working fluid may fall via gravity toward the second portion 152 and may flow across (e.g., flow around, flow over) the tubes 163 of the combination heat exchanger 70. Because the liquid high side working fluid discharged into the combination heat exchanger 70 has a lower temperature than the low side working fluid directed through the tubes 163, as the high side working fluid flows over and / or across the tubes 163, the low side working fluid may transfer heat to the high side working fluid, thereby causing portions of each of the high side working fluid and the low side working fluid to change phases. For example, as the vaporous low side working fluid transfers or deposits heat to the high side working fluid, the vaporous low side working fluid may decrease in temperature, thereby causing the low side working fluid to condense into a liquid low side working fluid. The liquid low side working fluid is then discharged toward the low side working fluid receiver 176, as described above.

[0052] Further, as the liquid high side working fluid receives heat from the low side working fluid, the liquid high side working fluid may increase in temperature, thereby causing the liquid high side working fluid to evaporate or vaporize into a vaporous high side working fluid. The vaporous high side working fluid may be collected by the conduit 158 and delivered to the compressor 50 (e.g., via the ports 160) for recirculation through the high side working fluid assembly 20, as described above. In certain embodiments, as the liquid high side working fluid is discharged into the first portion 150 of the second section 132, the decrease in pressure (e.g., as a result of passing through the expansion valve 54 and / or as a result of being discharged into a larger volume) may cause a portion of the high side working fluid to flash and / or change phases (e.g., vaporize). Such vaporous high side working fluid may also be collected by the conduit 158 and delivered to the compressor 50 (e.g., via the ports 160) for recirculation through the high side working fluid assembly 20. Thus, as noted above, in certain embodiments, the first portion 150 of the second section 132 may serve as a surge drum vessel for the high side working fluid.

[0053] Additionally, as noted above, in certain embodiments, lubricant may be present within the high side working fluid flow, and the high side lubricant return vessel 159 may be configuredto receive and / or collect lubricant that has been separated from the high side working fluid, and direct the lubricant back to the compressor 50 (e.g., via the high side lubricant return assembly 51). For example, a density of lubricant within a high side working fluid flow may be greater than a density of vaporous and / or liquid high side working fluid. Thus, as the high side working fluid exchanges heat with the low side working fluid directed through the tubes 163 and vaporizes, lubricant within the vaporous high side working fluid may fall via gravity toward the tube partition plate 169. The lubricant may then pass through the tube partition plate 169 (e.g., via the multiple passages) and be collected by the high side lubricant return vessel 159. Further, in certain embodiments, lubricant may naturally separate from liquid high side working fluid due to the difference in density, thereby enabling lubricant to fall via gravity toward the high side lubricant return vessel 159 for recirculation back to the compressor 50.

[0054] FIG. 4 is a longitudinal cross-sectional view of an embodiment of the second section 132 of the combination heat exchanger 70. In the illustrated embodiment, the second section 132 includes the first portion 150 having the conduit 158, the second portion 152 having the tube support assembly 161 with the tube supports 164 configured to support the tubes 163, and the third portion 154 having the high side lubricant return vessel 159. As noted above, the second portion 152 may be separated from the third portion via the tube partition plate 169, and the tube partition plate 169 may be include multiple passages 180 configured to enable lubricant separated from the high side working fluid to pass through the second portion 152 of the second section 132 and into the third portion 154 of the second section 132 (e.g., via gravity) to be collected by the high side lubricant return vessel 159.

[0055] As noted above, the tube support assembly 161 may include multiple tube supports 164, and each of the tube supports 164 may be configured to support a plurality of tubes 163 extending therethrough. For example, each tube support 164 of the tube support assembly 161 may be coupled (e.g., via welding, integrally coupled via an injection molding process, etc.) to the body 162 of the tube support assembly 161 any may extend from the body 162 and across the second portion 152 of the second section 132 in a direction (e.g., vertical direction, horizontal direction) along the lateral axis 112 and the vertical axis 114. That is, the tube supports 164 may extend cross-wise relative to a direction in which the tubes 163 of the combination heat exchanger 70 extend (e.g., cross-wise to the directions 167, 168). Each tube support 164 may include ordefine multiple passages 190 extending therethrough in a direction (e.g., horizontal direction) along the longitudinal axis 110, and each of the passages 190 may be configured to receive and support a respective tube 163. In certain embodiments, the tube supports 164 employed by the combination heat exchanger 70 may at least partially define the first pass 165 and the second pass 166 of the tubes 163. For example, each tube support 164 may include a first set 191 of passages 190 oriented along the first pass 165 of the tubes 163 and a second set 192 of passages 190 oriented along the second pass 166 of the tubes 163. The first set 191 of passages 190 may be positioned above the second set 192 of passages 190 relative to gravity such that the first pass 165 of the tubes 163 is also positioned above the second pass 166 of the tubes 163 relative to gravity. Further, the first set 191 of passages 190 may be spaced apart from the second set 192 of passages 190 by a space 194 (e.g., gap). A size of the space 194 may be selected based on design characteristics of the heat exchange tubes 163 (e.g., a bend radius of the tubes 163 as the tubes 163 transition from the first pass 165 to the second pass 166 within the third section 134). Each of the passages 190 may be configured to support a respective tube 163 of the combination heat exchanger 70. Thus, in certain embodiments, a number of tubes 163 employed by the combination heat exchanger 70 may correspond to a number of passages 190 within each of the tube supports 164. However, it should be noted that the combination heat exchanger 70 may include fewer tubes 163 than passages 190.

[0056] FIG. 5 is a perspective view of an embodiment of a portion of a tube sheet 128 employed by the combination heat exchanger 70. As discussed above, the combination heat exchanger 70 may employ one or more tube sheets 128 to separate the combination heat exchanger 70 into various sections (e.g., first section 130, second section 132, third section 134). Further, each tube sheet 128 may be configured to support the tubes 163, and in certain embodiments, the tube sheets 128 may also at least partially define the first pass 165 and the second pass 166 of the tubes 163. In certain embodiments, each tube sheet 128 may also be configured to provide an alert when a potential leak of low side working fluid into the high side working fluid is detected, which may form undesirable compounds (e.g., ammonium carbamate). For example, each tube sheet 128 may include a body 200 that extends in a direction (e.g., vertical direction, horizontal direction) along the vertical axis 114 and the lateral axis 112 (e.g., extends in a direction cross-wise to the directions 167, 168). The body 200 of each tube sheet 128 may define multiple passages 202 extending therethrough in a direction (e g., horizontal direction) along the longitudinal axis 110.Each passage 202 may be configured to support and / or receive a tube 163 of the combination heat exchanger 70.

[0057] In certain embodiments, the body 200 of the tube sheet 128 may be separated into a first portion 204 (e.g., welded portion) and a second portion 206 (e.g., expanded portion). The second portion 206 may further include one or more grooves 208 (e.g., expansion grooves) fluidly coupled to one or more ports 210. For example, the one or more ports 210 may be drilled and / or tapped through the body 200 of the tube sheet in a direction crosswise to the longitudinal axis 110 (e.g., radial direction) and may fluidly couple to the one or more grooves 208. In certain embodiments, the one or more ports 210 may separate the first portion 204 from the second portion 206. The grooves 208 and the port(s) 210 may be configured to determine when potential leak conditions exist, thereby enabling an operator to suspend operation of the cascade refrigeration system 10 to address the potential leak. For example, the tubes 163 of the combination heat exchanger 70 extending through the first portion 204 and the second portion 206 of the tube sheet 128 may be welded to the tube sheet 128 within the first portion 204 and the second portion 206 to create a seal between the tube sheet 128 and the tubes 163. Because there are grooves 208 within the second portion 206, the coupling between the tube sheet 128 and the tubes 163 may be referred to herein as a tube expansion joint, and at least a portion of the tubes 163 extending through the second portion 206 may not be welded to the tube sheet 128 (e.g., portion of the tubes 163 extending across or over the grooves 208).

[0058] As the tubes 163 direct low side working fluid therethrough, if one of the tube expansion joints fails (e.g., if low side working is directed into one of the grooves 208), one or more of the grooves 208 may receive low side working fluid, thereby causing a pressure increase within the one or more grooves 208. Further, each of the ports 210 may include a pressure switch 212 fluidly coupled to the grooves 208. Thus, the pressure switch 212 may be configured to detect an increase in pressure in the one or more grooves 208, which may provide an indication that a potential leak condition exists. Upon detecting the increase in pressure, the pressure switch 212 may send such data (e.g., a signal) to the controller 100, thereby enabling the controller 100 to provide a notification (e.g., alert, message, warning) to an operator of the cascade refrigeration system 10, which may include a recommendation to address the potential leak conditions. In certain embodiments, the controller 100 may be configured to suspend (e.g., automaticallysuspend) operation of the combination heat exchanger 70 and / or suspend operation of the cascade refrigeration system 10 (e.g., suspend operation of the high side working fluid assembly 20, suspend operation of the low side working fluid assembly 22, suspend operation of the compressors 50, 60) upon detecting the increase in pressure (e.g., upon detecting that a pressure within the grooves 208 as detected by the pressure switch 212 exceeds a predetermined pressure threshold value). In certain embodiments, an entire dimension (e.g., length) of the tubes 163 extending through the first portion 204 of the tube sheet 128 may be welded to the first portion 204 of the tube sheet 128, whereas certain portions of the tubes 163 extending through the second portion 206 may be welded to the tube sheet 128 while remaining portions (e.g., portions that pass over the grooves 208) are not welded to the tube sheet 128. In this way, the low side working fluid may be blocked from mixing with the high side working fluid within the first portion 204 of the tube sheet 128.

[0059] FIG. 6 is a lateral cross-sectional view of an embodiment of the first section 130 of the combination heat exchanger 70. In the illustrated embodiment, the first section 130 includes the partition plate 144 which divides or separates the first section 130 into the first chamber 140 and the second chamber 142. The first chamber 140 is configured to receive saturated low side working fluid (e.g., low side working fluid / lubricant mixture) via the low side working fluid inlet 146, and the saturated low side working fluid may be directed through the low side lubricant separator 148. As noted above, the low side lubricant separator 148 may be configured to separate lubricant from the low side working fluid (e.g., vaporous low side working fluid), thereby enabling substantially low side working fluid (e.g., low side working fluid that has less than a threshold amount oflubricant) to be directed through the tube sheet 128 and into tubes 163 extending through the second section 132 via a low side working fluid discharge port 220 (e.g., manifold). For example, the low side working fluid discharge port 220 may be fluidly coupled to an interior of the tubes 163 of the combination heat exchanger 70, thereby enabling low side working fluid to be directed from the first section 130 into the tubes 163 to exchange heat with high side working fluid directed across the tubes 163, as described above.

[0060] In certain embodiments, the low side lubricant separator 148 may include multiple components configured to facilitate separation of the lubricant from the low side working fluid directed into the first section 130. For example, the low side lubricant separator 148 may includea conduit 230 (e.g., perforated conduit) that is fluidly coupled to the low side working fluid discharge port 220, and an encapsulator 232 (e.g., porous material, steel wool) wrapped around a circumference of the conduit 230. For example, during manufacture and / or assembly of the low side lubricant separator 148, the encapsulator 232 may be wrapped around the circumference of the conduit 230 multiple times, thereby forming multiple layers of material configured to encapsulate the conduit 230. However, the encapsulator 232 may be composed of a porous material such that as vaporous low side working fluid is directed through the first chamber 140 of the first section, lubricant present within the vaporous low side working fluid may be blocked from traveling toward the conduit 230 via the encapsulator 232. For example, the encapsulator 232 may be composed of a material that readily enables vaporous working fluid to flow therethrough while limiting or blocking an amount of lubricant from flowing therethrough. In this way, lubricant may be separated from the low side working fluid before the low side working fluid is directed into the tubes 163 via the low side working fluid discharge port 220. The lubricant that is separated from the low side working fluid may be directed into the lubricant return conduit 149, thereby enabling the lubricant to be returned to the compressor 60 (e.g., via the low side lubricant return assembly 61 fluidly coupled to the lubricant return conduit 149).

[0061] Additionally, as noted above, as the low side working fluid is condensed within the heat exchange tubes 163 via the heat exchange relationship with the high side working fluid directed across the tubes 163, liquid low side working fluid may be discharged into the second chamber 142 (e.g., into the basin 174) of the first section 130. However, because a volume of the second chamber 142 (e.g., a volume of the basin 174) is significantly greater than a volume within the heat exchange tubes 163, as the liquid low side working fluid is directed into the second chamber 142, the increase in volume may result in a pressure drop, thereby causing a portion of the liquid low side working fluid to change phases (e.g., vaporize, flash) within the second chamber 142 (e.g., within the basin 174) and / or the low side working fluid receiver 176. The vaporous low side working fluid may be directed through passages 180 extending through the partition plate 144

[0062] As set forth above, the present disclosure may provide one or more technical effects useful in manufacturing, transporting, and assembling cascade refrigeration systems. Embodiments of the present disclosure may include a combination heat exchanger configured to house a number of components that are traditionally embodied as separate ancillary componentsin traditional cascade refrigeration systems. For example, the combination heat exchangers discussed herein may include a section configured to separate vaporous ammonia from liquid ammonia, thereby serving as a surge drum vessel. Additionally, the combination heat exchangers may include a lubricant processing system (e.g., lubricant processing assembly) and a carbon dioxide receiver vessel, thereby serving as the lubricant pot and lubricant separator vessels and the carbon dioxide receiver vessels, respectively. Further still, the combination cascade heat exchangers discussed herein may include a specialized tube sheet configured to detect the presence of ammonium carbamate, thereby serving as an ammonium carbamate isolation system. By including each of the above described components into a single combination heat exchanger, costs associated with the manufacture, transportation, and assembly of cascade refrigeration systems employing a combination heat exchanger may be reduced. For example, the reduction in space and weight by virtue of employing fewer separate components may enable an industrial CO2 / NH3 cascade refrigeration system to be assembled in a compact package that may be transported in one piece. Further, the service and manufacturing simplicity of a single, compact package enables the system to be standardized and automated, thereby further increasing savings associated with the manufacture and assembly of such refrigeration systems. The technical effects and technical problems in the specification are examples and are not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems.

[0063] 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 suchactual 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

CLAIMS:

1. A cascade refrigeration system, comprising: a high side working fluid assembly configured to circulate a high side working fluid therethrough; a low side working fluid assembly configured to circulate a low side working fluid therethrough; and a combination heat exchanger, comprising: a first section comprising: a low side lubricant separator configured to separate lubricant from the low side working fluid; and a low side working fluid receiver; and a second section comprising: a plurality of heat exchange tubes configured to receive the low side working fluid and direct the low side working fluid therethrough; a high side working fluid inlet configured to receive the high side working fluid and place the high side working fluid into a heat exchange relationship with the low side working fluid; and a high side lubricant return vessel configured to receive additional lubricant from the high side working fluid.

2. The cascade refrigeration system of claim 1, wherein the second section comprises a first portion, a second portion, and a third portion, the first portion is above a central axis of the combination heat exchanger relative to gravity, the second portion and the third portion are below the central axis relative to gravity, the plurality of heat exchange tubes extend within the second portion, and the high side lubricant return vessel is positioned within the third portion.

3. The cascade refrigeration system of claim 2, wherein the second section comprises a conduit extending within the first portion and configured to receive vaporized high side working fluid via the heat exchange relationship between the low side working fluid and the high side working fluid.

4. The cascade refrigeration system of claim 2, wherein the second section comprises a partition plate separating the second portion and the third portion, wherein the partition plate comprises a plurality of passages configured to separate the additional lubricant from the side working fluid.

5. The cascade refrigeration system of claim 1, wherein the second section comprises one or more tube sheets configured to support the plurality of heat exchange tubes, wherein each of the one or more tube sheets comprises a plurality of grooves configured to receive the low side working fluid.

6. The cascade refrigeration system of claim 5, wherein the one or more tube sheets are configured to detect a leak within at least one of the plurality of heat exchange tubes based on an amount of the low side working fluid within the plurality of grooves.

7. The cascade refrigeration system of claim 1, wherein the first section comprises a partition plate separating the first section into a first chamber and a second chamber, the low side lubricant separator is disposed within the first chamber, and the low side working fluid receiver is disposed within the second chamber.

8. The cascade refrigeration system of claim 7, wherein the second chamber defines a basin configured to receive liquid low side working fluid from the plurality of heat exchange tubes and direct the liquid low side working fluid into the low side working fluid receiver.

9. The cascade refrigeration system of claim 1, wherein the second section comprises a tube support assembly comprising a plurality of tube supports configured to support the plurality of heat exchange tubes, wherein the tube support assembly at least partially defines a first pass of the plurality of heat exchange tubes and a second pass of the plurality of heat exchange tubes.

10. The cascade refrigeration system of claim 1, wherein the high side working fluid is ammonia, and the low side working fluid is carbon dioxide.

11. A combination heat exchanger for a cascade refrigeration system, comprising: a first tube sheet and a second tube sheet configured to separate the combination heat exchanger into a first section, a second section, and a third section; a low side lubricant separator positioned within a first chamber of the first section and configured to separate lubricant from a low side working fluid and direct the low side working fluid toward the second section; a high side working fluid inlet fluidly coupled to the second section and configured to direct a high side working fluid into the second section; a plurality of heat exchange tubes extending within the second section and configured to receive the low side working fluid from the low side lubricant separator, transfer heat from the low side working fluid to the high side working fluid directed across the plurality of heat exchange tubes, and discharge the low side working fluid into a second chamber of the first section; a conduit extending within the second section and configured to receive vaporized high side working fluid and direct the vaporized high side working fluid out of the combination heat exchanger; and a low side working fluid receiver fluidly coupled to the second chamber of the first section and configured to receive the low side working fluid from the plurality of heat exchange tubes.

12. The combination heat exchanger of claim 11, comprising a high side lubricant return vessel configured to receive additional lubricant from the high side working fluid.

13. The combination heat exchanger of claim 11, wherein each of the first tube sheet and the second tube sheet are configured to detect a leak within the plurality of heat exchange tubes.

14. The combination heat exchanger of claim 11, wherein the low side lubricant separator comprises an encapsulator configured to separate the lubricant from the low side working fluid.

15. The combination heat exchanger of claim 14, wherein the encapsulator comprises a porous material.

16. The combination heat exchanger of claim 14, wherein the encapsulator is steel wool.

17. A cascade refrigeration system, comprising: a high side working fluid vapor compression circuit comprising a first compressor configured to circulate a high side working fluid through the high side working fluid vapor compression circuit; a low side working fluid vapor compression circuit comprising a second compressor configured to circulate a low side working fluid through the low side working fluid vapor compression circuit; a combination heat exchanger configured to: receive the low side working fluid via a plurality of tubes; receive the high side working fluid via a high side working fluid inlet; condense the low side working fluid and evaporate the high side working fluid via heat exchange between the low side working fluid and the high side working fluid; and separate lubricant from the low side working fluid and additional lubricant from the high side working fluid; and a controller configured to control operation of the combination heat exchanger to satisfy a cooling load on the low side working fluid vapor compression circuit.

18. The cascade refrigeration system of claim 17, wherein the combination heat exchanger comprises one or more tube sheets configured to support the plurality of tubes and detect a leak within the plurality of tubes.

19. The cascade refrigeration system of claim 18, wherein each of the one or more tube sheets comprises a plurality of grooves fluidly coupled to a pressure switch, wherein the pressure switch is configured to detect the leak when a pressure within the plurality of grooves exceeds a threshold pressure value.

20. The cascade refrigeration system of claim 19, wherein the controller is configured to: receive a signal from the pressure switch indicative of the pressure exceeding the threshold pressure value; and suspend operation of the combination heat exchanger based on the signal.

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