Abstract:
A thermal cycling system includes a structure defining a load space, a heating assembly positioned to heat to the load space, and a cooling assembly positioned to cool the load space. The cooling assembly includes a refrigeration circuit and a banking circuit. The refrigeration circuit has a compressor, a refrigeration condenser, a first refrigeration evaporator in direct thermal communication with the load space, a second refrigeration evaporator in parallel with the first evaporator, and primary refrigerant circulating throughout the refrigeration circuit. The banking circuit is gravity fed and includes a banking condenser, a banking evaporator positioned to cool the load space, and a banking refrigerant circulating throughout the banking circuit. The banking condenser includes a collection reservoir to store liquid banking refrigerant and is in thermal communication with the second refrigeration evaporator.

Description:
BACKGROUND 
     The present invention generally relates to test equipment, and specifically to test equipment for repetitive thermal cycling between high and low temperatures. 
     Thermal cycling test equipment, such as environmental test chambers, are commonly used to test products by subjecting them to thermal shock, i.e., rapidly transitioning between high and low temperature extremes with short dwells at each extreme. This type of testing results in inefficient use of a refrigeration system, which operates under high capacity requirements during the rapid cooling cycle and no cooling requirements for other intervals of the testing. To achieve the rapid cooling required, large capacity refrigeration systems relative to the workspace or product load are commonly utilized. 
     Thermal shock tests were previously performed by physically transporting a test product between separate heating and cooling chambers. The test product was transported by a human operator or a mechanical conveyor. Transport by a human operator created error in transition times between the high and low temperature extremes. Furthermore, movement of the test product created mechanical stresses and caused logistic difficulties if the test product needed to be plugged in, for example. 
     SUMMARY 
     The present invention provides a structure defining a load space, a heating assembly positioned to heat the load space, and a cooling assembly positioned to cool the load space. 
     In one aspect, the cooling assembly includes a refrigeration circuit having a compressor, a refrigeration condenser, a refrigeration evaporator, and primary refrigerant circulating throughout the refrigeration circuit, and a banking circuit having a banking condenser, a banking evaporator positioned to cool the load space, and a banking refrigerant circulating throughout the banking circuit. The banking condenser includes a collecting reservoir for collecting banking refrigerant, the collecting reservoir being in thermal communication with the refrigeration evaporator. 
     In another aspect, the cooling assembly includes a refrigeration circuit having a compressor, a refrigeration condenser, a refrigeration evaporator, and primary refrigerant circulating throughout the refrigeration circuit. The cooling assembly also includes a banking circuit having a banking condenser, a banking evaporator positioned in direct thermal communication with the load space, and a banking refrigerant circulating throughout the banking circuit. The banking circuit is gravity fed. 
     In yet another aspect, the cooling assembly includes a refrigeration circuit having a compressor, a refrigeration condenser, a first refrigeration evaporator in direct thermal communication with the load space, a second refrigeration evaporator in parallel with the first evaporator, and primary refrigerant circulating throughout the refrigeration circuit. The cooling assembly also includes a banking circuit having a banking condenser, a banking evaporator positioned to cool the load space, and a banking refrigerant circulating throughout the banking circuit. The banking condenser is in thermal communication with the second refrigeration evaporator. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a thermal cycling system embodying the present invention. 
         FIG. 2  is a plot of time vs. temperature of the thermal cycling system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     The refrigeration system  10  shown in  FIG. 1  is used in an environmental test chamber or load space  12  in which products are thermally shocked by rapidly transitioning the test chamber environment  12  between heating and cooling operations (high and low temperature extremes). The refrigeration system  10  includes a low stage or primary refrigeration system  14  circulating a primary refrigerant, a fluidly separate high stage refrigeration system  26  circulating a secondary refrigerant, and a fluidly separate capacity banking circuit  30  circulating a banking refrigerant. The load space  12  also includes a heating assembly  94  to heat the load space  12  to the high temperature extreme. 
     A controller  98  is programmed to operate the refrigeration system  10  and the heating assembly  94  according to a programmed cycle of alternating between a heating mode and a cooling mode, which will be explained in greater detail below. 
     The primary refrigeration system  14  includes a first evaporator path  18  and a second evaporator path  22  in parallel with the first evaporator path  18 . The primary refrigeration system  14  includes a low stage compressor  34 , a low stage condenser  38 , a primary evaporator  42 , a secondary evaporator  46 , a first solenoid valve  102  and a first expansion valve  50  just upstream of the primary evaporator  42 , a second solenoid valve  104  and a second expansion valve  54  just upstream of the secondary evaporator  46 , and a check valve  106  just downstream of the secondary evaporator  46 . The primary evaporator  42  is positioned within the test chamber  12  in heat transfer communication with the test chamber  12  to cool the test chamber  12 . The first evaporator path  18  includes the low stage compressor  34 , the low stage condenser  38 , the first solenoid valve  102 , the first expansion valve  50 , and the primary evaporator  42 . The second evaporator path  22  includes the low stage compressor  34 , the low stage condenser  38 , the second solenoid valve  104 , the second expansion valve  54 , the secondary evaporator  46 , and the check valve  106 . The check valve  106  prevents reverse flow of primary refrigerant. Without the check valve  106 , warm primary refrigerant leaving the primary evaporator  42  could migrate toward and condense in the secondary evaporator  46 , thus releasing heat instead of absorbing it. Furthermore, this would cause the first evaporator path  18  to run low on primary refrigerant. 
     The high stage refrigeration system  26  includes a high stage compressor  74 , a high stage condenser  78  which may be air-cooled or water-cooled, a high stage evaporator  82 , and a high stage expansion valve  86  just upstream of the high stage evaporator  82 . The high stage evaporator  82  and the low stage condenser  38  form a cascade heat exchanger  90  in which the low stage condenser  38  rejects heat to the high stage evaporator  82  to cool and condense the primary refrigerant, as is well understood in the art. The high stage refrigeration system  26  can be operated to circulate secondary refrigerant to the high stage evaporator  82  when at least one of the first and second evaporator paths  18 ,  22  is running and therefore in need of cooling. 
     The capacity banking circuit  30  includes a capacity banking condenser  58 , a capacity banking evaporator  62  positioned within the test chamber  12  in heat transfer communication with the test chamber  12  to cool the test chamber  12 , a first isolation valve  66  (such as a ball valve) just upstream of the capacity banking evaporator  62 , and a second isolation valve  68  (such as a ball valve) just downstream of the capacity banking evaporator  62 . The capacity banking condenser  58  and the secondary evaporator  46  collectively form a capacity banking heat exchanger  70  in which the secondary evaporator  46  cools and condenses refrigerant in the capacity banking condenser  58  and cools the mass of the capacity banking heat exchanger  70 . 
     The capacity banking condenser  58  includes a collecting reservoir  72  for collecting banking refrigerant. Liquid banking refrigerant is stored in the collecting reservoir  72  to store cooling capacity for use when needed. When additional cooling capacity is needed (e.g., when the test chamber environment must be rapidly transitioned from hot to cold), the stored banking refrigerant is released, as described in greater detail below. The banking refrigerant circulates through the capacity banking circuit  30  by gravity and phase change circulation. The capacity banking condenser  58  and the collecting reservoir  72  are elevated with respect to the capacity banking evaporator  62 . Liquid banking refrigerant condensed in the capacity banking condenser  58 , having a higher density than vapor, falls to the capacity banking evaporator  62  by gravity when the isolation valve  66  is open. Banking refrigerant changing phase from liquid to vapor (evaporation) in the capacity banking evaporator  62  rises in pressure relative to the capacity banking condenser  58  and returns to the elevated capacity banking condenser  58  through a conduit, drawn to the area of lower pressure created by the vapor-to-liquid phase change (condensation) of the banking refrigerant in the capacity banking condenser  58 . In this way, liquid banking refrigerant is prevented from migrating to the capacity banking condenser  58  and vapor banking refrigerant is prevented from entering the capacity banking evaporator  62 . Thus, the liquid banking refrigerant is substantially kept separate from the vapor banking refrigerant. In this manner, the heat rejected from the load space  12  is efficiently moved to the capacity baking heat exchanger  70 . In other constructions, a pump may be employed to circulate the banking refrigerant. 
     The heating assembly  94  is positioned at least partially within the test chamber  12  to heat the test chamber  12  during a heating mode. The heating assembly  94  may include an electric heater, a steam heating circuit, a glycol heating circuit, or the like. 
     With reference to  FIG. 2 , the cooling mode includes a transition cooling mode that begins when cooling to a setpoint cooling temperature is first demanded and ends when the setpoint cooling temperature is reached. The cooling mode also includes a stabilization cooling mode that begins when the setpoint cooling temperature is reached and ends when the setpoint cooling temperature is no longer demanded (e.g., when heating is demanded, when the system  10  is shut off, etc. . . . ). The heating mode begins when heating is demanded and ends when heating is no longer demanded (e.g., when cooling is demanded and the transition cooling mode begins, when the system  10  is shut off, etc. . . . ). 
     Products are positioned within the test chamber  12  and are thermally shocked by the rapid alternating of extreme hot and cold temperatures. For example, to perform a Military standard test (in compliance with MIL-STD-883C 1010.7 method C), a product temperature change from 150° C. to −65° C. (302° F. to −85° F.) must occur in 15 minutes. A transition time is the duration of the transition cooling mode. Preferably, the transition time is short (e.g., 15 minutes) to thermally shock the products. 
     During the heating mode, the heating assembly  94  provides heat to the test chamber  12 . Furthermore, flow of the primary refrigerant in first evaporator path  18  is stopped, flow of the primary refrigerant in the second evaporator path  22  is continued to circulate the primary refrigerant to the secondary evaporator  46 , and flow of the banking refrigerant in the capacity banking circuit  30  is stopped. Thus, capacity banking occurs during the heating mode. To stop the flow of primary refrigerant in the first evaporator path  18 , a solenoid valve  102  is positioned just upstream of the first expansion valve  50 . When the solenoid valve  102  is closed, the primary refrigerant does not circulate to the primary evaporator  42 . Thus, the primary evaporator  42  does not provide cooling to the test chamber  12  during the heating mode. However, the primary refrigerant circulates to the secondary evaporator  46  during the heating mode. The primary refrigerant evaporates (i.e., vaporizes) in the secondary evaporator  46  to cool and condense banking refrigerant in the banking condenser  58  and to cool the mass of the banking heat exchanger  70 . Flow of the banking refrigerant in the capacity banking circuit  30  is stopped by closing the first isolation valve  66 . The second isolation valve  68  is open to allow banking refrigerant to migrate toward the capacity banking condenser  58 , to prevent the build up of pressure in an isolated section, as the banking refrigerant heats up and evaporates. Thus, the capacity banking evaporator  62  does not provide cooling to the test chamber  12  during the heating mode, and the second evaporator  46  and the capacity banking condenser  58  are operable to store cooling capacity during the heating mode. 
     During the transition cooling mode, all of the primary refrigerant is circulated to the primary evaporator  42  along the first evaporator path  18  to concentrate the cooling capacity of the primary refrigerant directly on the load space  12 . Furthermore, to provide additional cooling and reduce the transition time, banking refrigerant is circulated through the capacity banking circuit  30  to the capacity banking evaporator  62  to additionally cool the load space  12  using cooling capacity stored in the banking refrigerant and in the mass of the capacity banking heat exchanger  70 . The stored and cooled liquid banking refrigerant evaporates (i.e., vaporizes) in the capacity banking evaporator  62  and absorbs heat from the test chamber  12  to cool the test chamber  12 . The first isolation valve  66  is opened to release the stored liquid banking refrigerant to the capacity banking evaporator  62  for evaporation. The second isolation valve  68  is opened to allow vapor to return to the capacity banking condenser  58 . Thus, the capacity banking evaporator  62  provides rapid cooling to the test chamber  12  during the transition cooling mode by releasing cooling capacity stored in the form of liquid banking refrigerant to the capacity banking evaporator  62 . Furthermore, cooling capacity stored in the mass of the capacity banking heat exchanger  70  is transferred to the banking refrigerant as the banking refrigerant vapor returns from the capacity banking evaporator  62 , condenses in the capacity banking condenser  58  thus rejecting heat to the capacity banking heat exchanger  70 , and circulates back to the capacity banking evaporator  62 , providing further rapid cooling from stored cooling capacity during the transition cooling mode. 
     During the transition cooling mode, the pressure in the capacity banking evaporator  62  is monitored by the controller  98  with a pressure transducer (not shown) so that a saturation temperature of banking refrigerant in the capacity banking evaporator  62  can be determined. Alternatively, a temperature sensor may be provided in the banking circuit  30  to determine the saturation temperature of banking refrigerant directly. The temperature of the load space  12  is also monitored by the controller  98  with a temperature sensor (not shown). If the temperature of the load space  12  is greater than the saturation temperature in the capacity banking evaporator  62 , then the first and second isolation valves  66 ,  68  are open and the load space  12  is cooled. However, if the temperature of the load space  12  is lower than the saturation temperature, effective cooling of the load space  12  will not be provided and the controller  98  closes the first isolation valve  66  to prevent the circulation of banking refrigerant in the banking circuit  30 . 
     A draining circuit  108  is provided to drain banking refrigerant from the capacity banking evaporator  62  (bank draining) during the transition cooling mode when the saturation temperature of the banking refrigerant is higher than the temperature of the load space  12 . When the saturation temperature of the banking refrigerant in the capacity banking evaporator  62  is higher than the temperature of the load space  12 , the banking refrigerant becomes an added load on the load space  12 . Therefore, it is advantageous to remove the banking refrigerant from the capacity banking evaporator  62  to reduce the load on the load space  12 . The controller  98  closes the first and second isolation valves  66 ,  68  and liquid banking refrigerant is drained by opening a third isolation valve  112  (such as a ball valve) such that the liquid banking refrigerant drains by gravity into the draining circuit  108 . The liquid banking refrigerant flows by gravity to a recycle heat exchanger  110  in heat transfer communication with the high stage condenser  78 . Liquid banking refrigerant in the recycle heat exchanger is heated and vaporized by the high stage condenser  78 , and vapor banking refrigerant is directed to the capacity banking condenser  58  by phase change circulation. 
     During the stabilization cooling mode, the primary refrigeration system  14  circulates the primary refrigerant through the first evaporator path  18  (direct cooling) to maintain the setpoint cooling temperature and through the second evaporator path  22  (capacity banking) to store cooling capacity in the manner described above. The first solenoid valve  102  is opened to allow the primary refrigerant to flow to the primary evaporator  42 . Thus, the primary evaporator  42  provides cooling to the test chamber  12  during the stabilization cooling mode. The second solenoid valve  104  is open to allow the primary refrigerant to flow to the secondary evaporator  46 . Primary refrigerant is circulated to the secondary evaporator  46  along the second evaporator path  22 . Thus, the secondary evaporator  46  transfers cooling capacity to the capacity banking condenser  58  and the banking refrigerant during the stabilization cooling mode. However, the isolation valve  66  is closed so banking refrigerant is not circulated through the capacity banking circuit  30  to the capacity banking evaporator  62  during the cooling mode. Isolation valve  68  is closed to prevent refrigerant migration to the capacity banking evaporator  62  while the load space  12  is at low temperature stabilization. 
     In the preferred embodiment, the primary refrigerant is circulated through the second evaporator path  22  (capacity banking) during the heating mode and the stabilization cooling mode, but not the transition cooling mode. 
     The refrigeration system  10  stores cooling capacity during the heating mode and the stabilization cooling mode to be used when needed and provides rapid cooling (bank cooling) to the test chamber  12  during the transition cooling mode when the saturation temperature of the banking refrigerant is lower than the temperature of the load space  12 . In this way, a smaller refrigeration system can be used to achieve the same relative cooling performance, reducing the overall size of the equipment. Furthermore, the transition time is reduced. 
     Various features and advantages are set forth in the following claims.