Patent Publication Number: US-9845973-B2

Title: Cascade refrigeration system

Description:
FIELD 
     The disclosure relates to a refrigeration system, and more particularly to a cascade refrigeration system. 
     BACKGROUND 
     Referring to  FIG. 1 , a single refrigerant refrigeration system includes a compressor  11 , a condenser  12  disposed downstream of and fluidly connected to the compressor  11 , an expansion valve  13  disposed downstream of and fluidly connected to the condenser  12 , and an evaporator  14  disposed downstream of the expansion valve  13  and upstream of the compressor  11 . 
     During operation of the refrigeration system, a refrigerant  101  flows into the compressor  11  and is compressed into a high-temperature and high-pressure gasified refrigerant  101 , after which it flows into the condenser  12  and is condensed into a normal-temperature and high-pressure liquefied refrigerant  101 . Next, the normal-temperature and high-pressure liquefied refrigerant  101  flows into the expansion valve  13  and is converted into a low-temperature and low-pressure liquefied refrigerant  101 . Afterwards, the low-temperature and low-pressure liquefied refrigerant  101  flows into the evaporator  14 , absorbs heat, and is converted into a low-temperature and low pressure gasified refrigerant  101  which then flows back into the compressor  11 . The existing single refrigerant refrigeration system is generally used in an air conditioning system and a refrigeration system. However, the cooling temperature of the existing single refrigerant refrigeration system ranges between 10° C. and 30° C. If a lower temperature refrigeration system is required, a dual refrigerant refrigeration system must be used. 
     Referring to  FIG. 2 , an existing dual refrigerant refrigeration system includes a liquefaction unit  15  and a cooling unit  16 . The liquefaction unit  15  includes a liquefaction compressor  151 , a liquefaction condenser  152  fluidly connected to the liquefaction compressor  151 , a liquefaction expansion valve  153  fluidly connected to the liquefaction condenser  152 , and a heat exchanger  154  fluidly interconnecting the liquefaction expansion valve  153  and the liquefaction compressor  151 . The cooling unit  16  includes a cooling compressor  161  fluidly connected to the heat exchanger  154 , a cooling expansion valve  162  fluidly connected to the heat exchanger  154 , and a cooling evaporator  163  fluidly connected to the cooling expansion valve  162  and the cooling compressor  161 . 
     The liquefaction unit  15  uses, for example, R404A or R507 refrigerant  105 , which can be liquefied at high pressure and normal temperature. The cooling unit  16  uses, for example, R23 refrigerant  106 , which cannot be liquefied at high pressure and normal temperature. By virtue of the heat exchanger  154 , the refrigerant  105  of the liquefaction unit  15  can liquefy the refrigerant  106  of the cooling unit  16  so that the refrigeration system can provide a cooling temperature of about −85° C. 
     When a wide range of the cooling temperature is required, the existing practice is to equip the refrigeration system with the single refrigerant refrigeration system and the dual refrigerant refrigeration system simultaneously. However, the production and maintenance costs of these two refrigeration systems are not only relatively high, but also they occupy a substantial space. 
     SUMMARY 
     Therefore, an object of the disclosure is to provide a cascade refrigeration system that can alleviate at least one of the drawbacks of the prior arts. 
     According to the disclosure, a cascade refrigeration system includes a first cooling device, a second cooling device and a circulation switching device. 
     The first cooling device includes a first compressor, a condenser disposed downstream of the first compressor, a first expansion device disposed downstream of the condenser, an evaporator disposed downstream of the first expansion device, and a first conduit that fluidly interconnects the first compressor, the condenser, the first expansion device and the evaporator and that is configured to circulate a first refrigerant. The evaporator has a first passage connected to the first conduit, and a second passage independent from and not communicating with the first passage. 
     The second cooling device includes a second compressor, a heat exchanger disposed downstream of the second compressor, and a second conduit fluidly interconnecting the heat exchanger, the second passage and the second compressor. 
     The circulation switching device includes a switching mechanism connected to the first conduit downstream of the condenser and upstream of the first expansion device, a circulation pipeline fluidly interconnecting the switching mechanism, the heat exchanger and the first compressor, and a circulation expansion device connected to the circulation pipeline downstream of the switching mechanism and upstream of the first heat exchanger. The switching mechanism is switchable between a first position, where the first refrigerant flows through the switching mechanism, the first expansion device, the first passage and back into the first compressor along the first conduit, and a second position, where the first refrigerant flows through the switching mechanism, the circulation expansion device, the heat exchanger and back into the first compressor along the circulation pipeline. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  is a schematic diagram illustrating a conventional single refrigerant refrigeration system; 
         FIG. 2  is a schematic diagram illustrating a conventional dual refrigerant refrigeration system; 
         FIG. 3  is a schematic diagram of a first embodiment of a cascade refrigeration system according to the disclosure, illustrating a first switching mechanism of the cascade refrigeration system at a first position; 
         FIG. 4  is a schematic diagram of the first embodiment illustrating the first switching mechanism at a second position; 
         FIG. 5  is a schematic diagram of a second embodiment of a cascade refrigeration system according to the disclosure, illustrating a second switching mechanism of the cascade refrigeration system at a third position; and 
         FIG. 6  a schematic diagram of the second embodiment, illustrating the second switching mechanism at a fourth position. 
     
    
    
     DETAILED DESCRIPTION 
     Before the disclosure is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
     Referring to  FIG. 3 , a cascade refrigeration system of a first embodiment according to the disclosure includes a first cooling device  2 , a second cooling device  3  and a circulation switching device  4 . 
     The first cooling device  2  includes a first compressor  21 , a condenser  22  disposed downstream of the first compressor  21 , a first expansion device  23  disposed downstream of the condenser  22 , an evaporator  24  disposed downstream of the first expansion device  23  and upstream of the first compressor  21 , and a first conduit  25  that fluidly interconnects the first compressor  21 , the condenser  22 , the first expansion device  23  and the evaporator  24  and that is configured to circulate a first refrigerant  200  which can be liquefied at high pressure and normal temperature. 
     In this embodiment, the first refrigerant  200  is R507 refrigerant, and the first expansion device  23  is a capillary tube which is used to reduce pressure and temperature of the first refrigerant  200 . In practice, the first expansion device  23  may be an expansion valve which can achieve the same effect of the capillary tube. 
     The evaporator  24  has a first passage  241  connected to the first conduit  25 , and a second passage  242  independent from and not communicating with the first passage  241 . 
     In this embodiment, the first cooling device  2  further includes a first oil-gas separator  261  fluidly connected to the first conduit  25  downstream of the first compressor  21  and upstream of the condenser  22 , a first high pressure gauge  262  connected to the first conduit  25  between the first oil-gas separator  261  and the condenser  22 , a first liquid receiver  263  fluidly connected to the first conduit  25  downstream of the condenser  22 , and a first filter drier  264  fluidly connected to the first conduit  25  downstream of the first liquid receiver  263  and upstream of the circulation switching device  4 . The first oil-gas separator  261  can separate a lubricant oil of the first compressor  21  and the first refrigerant  200 . The first liquid receiver  263  can separate the gasified first refrigerant  200  and the liquefied first refrigerant  200 , and can store the liquefied first refrigerant  200 . The first filter drier  264  can remove water vapor, moisture and impurities contained in the first refrigerant  200 . 
     The second cooling device  3  includes a second compressor  31 , a first heat exchanger  32  disposed downstream of the second compressor  31 , and a second conduit  33  fluidly interconnecting the first heat exchanger  32 , the second passage  242  and the second compressor  31 . The second conduit  33  is configured to circulate a second refrigerant  201  that cannot be liquefied at high pressure and normal temperature. In this embodiment, the second refrigerant  201  is R23 refrigerant. 
     Besides, the second cooling device  3  further includes a second oil-gas separator  341  fluidly connected to the second conduit  33  downstream of the second compressor  31 , a second high pressure gauge  342  connected to the second conduit  33  between the second oil-gas separator  341  and the first heat exchanger  32 , a second liquid receiver  343  fluidly connected to the second conduit  33  downstream of the first heat exchanger  32 , and a second filter drier  344  fluidly connected to the second conduit  33  downstream of the second liquid receiver  343  and upstream of the second passage  242 . Because the effects of the second oil-gas separator  341 , the second liquid receiver  343  and the second filter drier  344  are respectively similar to those of the first oil-gas separator  261 , the first liquid receiver  263  and the first filter drier  264 , the details thereof are omitted herein. 
     The circulation switching device  4  includes a first switching mechanism  411  connected to the first conduit  25  downstream of the condenser  22  and the first filter drier  264  and upstream of the first expansion device  23 , a first circulation pipeline  412  fluidly interconnecting the first switching mechanism  411 , the first heat exchanger  32  and the first compressor  21 , and a first circulation expansion device  413  connected to the first circulation pipeline  412  downstream of the first switching mechanism  411  and upstream of the first heat exchanger  32 . 
     In this embodiment, the first switching mechanism  411  is a two-position three-way solenoid valve. The first circulation expansion device  413  is a capillary tube which is used to reduce pressure and temperature of the first refrigerant  200 . In practice, the first expansion device  23  may be an expansion valve which can achieve the same effect of the capillary tube. 
     The first switching mechanism  411  is switchable between a first position, as shown in  FIG. 3 , and a second position, as shown in  FIG. 4 . 
     With reference to  FIG. 3 , when the first switching mechanism  411  is in the first position, the second compressor  31  is turned off such that the second refrigerant  201  is stopped from circulating along the second conduit  33 . 
     Meanwhile, the first refrigerant  200  flows into the first compressor  21  along the first conduit  25 , and is compressed into a high-temperature and high-pressure gasified first refrigerant  200 . The high-temperature and high-pressure gasified first refrigerant  200  then flows through the first oil-gas separator  261  into the condenser  22  and is condensed into a normal-temperature and high-pressure liquefied first refrigerant  200  which is stored in the first liquid receiver  263 . Next, the normal-temperature and high-pressure liquefied first refrigerant  200  exits from the first liquid receiver  263  and flows through the first filter drier  264  and the first switching mechanism  411  into the first expansion device  23 , where the normal-temperature and high-pressure liquefied first refrigerant  200  is converted into a low-temperature and low-pressure liquefied first refrigerant  200 . The low-temperature and low-pressure liquefied first refrigerant  200  exiting from the first expansion device  23  then flows through the first passage  241 , absorbs heat, and is converted into a low-temperature and low-pressure gasified first refrigerant  200 , so that the evaporator can provide a cooling temperature about −50° C. Afterwards, the low-temperature and low-pressure gasified first refrigerant  200  flows back into the first compressor  21  to complete a thermodynamic cycle in the first cooling device  2 . 
     With reference to  FIG. 4 , when the switching mechanism  411  is in the second position, the normal-temperature and high-pressure liquefied first refrigerant  200  exiting from the first liquid receiver  263  flows to the first circulation expansion device  413  through the first filter drier  264  and the switching mechanism  411 . Meanwhile, the first refrigerant  200  in the first passage  241  is temporarily stopped from circulating. The normal-temperature and high-pressure liquefied first refrigerant  200  is converted into a low-temperature and low-pressure liquefied first refrigerant  200  after passing through the first circulation expansion device  413 , and flows into the first heat exchanger  32 . Through the first heat exchanger  32 , the low-temperature and low-pressure liquefied first refrigerant  200  is converted into a low-temperature and low-pressure gasified first refrigerant  200  after absorbing heat in the first heat exchanger  32 , and then flows back into the first compressor  21  along the first circulation pipe  412  for continuous circulation in the first cooling device  2 . 
     When the temperature of the first refrigerant  200  is sufficient to liquefy the second refrigerant  201  during heat exchange in the first heat exchanger  32 , the second compressor  31  is turned on to compress the second refrigerant  201  that flows therein into a high-temperature and high-pressure gasified second refrigerant  201 . The high-temperature and high-pressure gasified second refrigerant  201  exiting from the second compressor  31  then flows to the first heat exchanger  32  through the second oil-gas separator  341  along the second conduit  33 . At the first heat exchanger  32 , the low-temperature and low-pressure liquefied first refrigerant  200  exchanges heat with the high temperature and high-pressure gasified second refrigerant  201  to convert the second refrigerant  201  into a low-temperature and high-pressure liquefied second refrigerant  201  which then flows to the evaporator  24  through the second liquid receiver  343  and the second filter drier  344 . The low-temperature and low-pressure liquefied second refrigerant  201  flows through the second passage  242  of the evaporator  24 , absorbs heat, and is converted into a low-temperature and low-pressure gasified second refrigerant  201 , so that the evaporator  24  can provide a cooling temperature of below −50° C. or even −70° C. Afterwards, the low-temperature and low-pressure gasified second refrigerant  201  flows back into the second compressor  31  for continuous circulation in the second cooling device  3 . It should be noted that when the second refrigerant  201  is circulating in the second passage  242  of the evaporator  24 , the first refrigerant  200  in the first passage  241  is temporarily stopped from circulating in the evaporator  24 . 
     By using the first and second passages  241 ,  242  of the evaporator  24  which are independent from and not communicating with each other, in cooperation with the first switching mechanism  411  which is switchable between first and second positions, the cascade refrigeration system of this embodiment simultaneously has the cooling capacity of a single refrigerant refrigeration system and a dual refrigerant refrigeration system, thereby reducing costs of the refrigeration system and space wastage. 
       FIG. 5  illustrates a cascade refrigeration system of a second embodiment according to the present disclosure. The structure and the operation of the second embodiment are similar to those of the first embodiment. The differences between the first and second embodiments reside in that the cascade refrigeration system further includes a third cooling device  5 , and the circulation switching device  4  further includes a second switching mechanism  421 , a second circulation pipeline  422  and a second circulation expansion device  423 . Moreover, the evaporator  24  further has a third passage  243  independent from and not communicating with the first and second passages  241 ,  242 , and the second cooling device  3  further includes a second expansion device  35  fluidly connected to the second conduit  33  downstream of the first heat exchanger  32  and upstream of the evaporator  24 . In this embodiment, the second expansion device  35  is a capillary tube. 
     The third cooling device  5  includes a third compressor  51 , a second heat exchanger  52  disposed downstream of the third compressor  51 , and a third conduit  53  fluidly interconnecting the third compressor  51 , the second heat exchanger  52  and the third passage  243 . The third conduit  53  is configured to circulate a third refrigerant  202 . In this embodiment, the third refrigerant  202  is a mixed refrigerant that is mixed and adjusted by a user himself according to his requirement. 
     Besides, the third cooling device  5  further includes a third oil-gas separator  541  fluidly connected to the third conduit  53  downstream of the third compressor  51 , a third high pressure gauge  542  connected to the third conduit  53  between the third oil-gas separator  541  and the second heat exchanger  52 , a third liquid receiver  543  fluidly connected to the third conduit  53  downstream of the second heat exchanger  52 , and a third filter drier  544  fluidly connected to the third conduit  53  downstream of the third liquid receiver  543  and upstream of the third passage  243 . Because the functions of the third oil-gas separator  541 , the third liquid receiver  543  and the third filter drier  544  are respectively similar to those of the first oil-gas separator  261 , the first liquid receiver  263  and the first filter drier  264 , the details thereof are omitted herein. 
     In this embodiment, the second switching mechanism  421  is a two-position three-way solenoid valve connected to the second conduit  33  downstream of the second filter drier  344  and upstream of the second expansion device  35 . The second circulation pipeline  422  fluidly interconnects the second switching mechanism  421 , the second heat exchanger  52  and the second compressor  31 . The second circulation expansion device  423  is a capillary tube connected to the second circulation pipeline  422  downstream of the second switching mechanism  421  and upstream of the second heat exchanger  52 . 
     The second switching mechanism  421  is switchable between a third position, as shown in  FIG. 5 , and a fourth position, as shown in  FIG. 6 . 
     With reference to  FIG. 5 , when the first switching mechanism  411  is in the second position and the second switching mechanism  421  is in the third position, the third compressor  51  is turned off so that the third refrigerant  202  is stopped from circulating along the third conduit  53 . Meanwhile, the normal-temperature and high-pressure liquefied second refrigerant  201  exiting from the first heat exchanger  32  flows to the second expansion device  35  through the second liquid receiver  343 , the second filter drier  344  and the second switching mechanism  421  along the second conduit  33 . By passing through the second expansion device  35 , the normal-temperature and high-pressure liquefied second refrigerant  201  is converted into a low-temperature and low-pressure liquefied second refrigerant  201 , after which it flows to the evaporator  24 . By passing through the second passage  242  of the evaporator  24 , the low-temperature and low-pressure liquefied second refrigerant  201  is converted into a low-temperature and low-pressure gasified second refrigerant  201 , so that the evaporator  24  can provide a cooling temperature lower than −50° C. or even below −70° C. Afterward, the low-temperature and low-pressure gasified first refrigerant  201  flows back into the second compressor  31  along the second conduit  33 . 
     With reference to  FIG. 6 , when the first switching mechanism  411  is in the second position and the second switching mechanism  421  is in the fourth position, the normal-temperature and high-pressure liquefied second refrigerant  201  exiting from the first heat exchanger  32  flows to the second circulation expansion device  423  through the second liquid receiver  343 , the second filter drier  344  and the second switching mechanism  421  along the second circulation pipeline  422 . When passing through the second circulation expansion device  423 , the normal-temperature and high-pressure liquefied second refrigerant  201  is converted into a low-temperature and low-pressure liquefied second refrigerant  201 , after which it flows to the second heat exchanger  52 . Through the second heat exchanger  52 , the low-temperature and low-pressure liquefied second refrigerant  201  absorbs heat and is converted into a low-temperature and low-pressure gasified second refrigerant  201 , after which it flows back into the second compressor  31  along the second circulation pipeline  422  for continuous circulation. 
     When the temperature of the second refrigerant  201  is sufficient to liquefy the third refrigerant  202  during heat exchange in the second heat exchanger  52 , the third compressor  51  is turned on, so that the third refrigerant  202  that flows into the third compressor  51  is compressed into a high-temperature and high-pressure gasified third refrigerant  202 . The high-temperature and high-pressure gasified third refrigerant  202  then flows to the second heat exchanger  52  through the third oil-gas separator  541  along the third conduit  53 . At the second heat exchanger  52 , the low-temperature and low-pressure liquefied second refrigerant  201  exchanges heat with the high-temperature and high-pressure gasified third refrigerant  202  to convert the high-temperature and high-pressure gasified third refrigerant  202  into a low-temperature and high-pressure liquefied third refrigerant  202  which then flows to the evaporator  24  through the third liquid receiver  543  and the third filter drier  544 . When the low-temperature and low pressure liquefied third refrigerant  202  flows through the third passage  243  of the evaporator  24 , it absorbs heat and is converted into a low-temperature and low-pressure gasified third refrigerant  202 , so that the evaporator  24  can provide a cooling temperature of about −100° C., which is lower than the cooling temperature provided by the evaporator  24  when the low-temperature and low-pressure liquefied second refrigerant  201  flows through the second passage  242 . Subsequently, the low-temperature and low-pressure gasified third refrigerant  202  flows back into the third compressor  51 . 
     It should be noted herein that when the third refrigerant  202  is circulating in the third passage  243  of the evaporator  24 , the first refrigerant  200  in the first passage  241  and the second refrigerant  201  in the second passage  242  are temporarily stopped from circulating in the evaporator  24 . Further, when the first switching mechanism  411  is in the first position (see  FIG. 3 ) and the second and third compressors  31 ,  51  are turned off, the first cooling device  2  can execute the cooling circulation, as shown in  FIG. 3 . 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least an implementation. The appearances of the phrase “in one embodiment” in various places in the specification may or may not be all referring to the same embodiment. Various features, aspects, and exemplary embodiments have been described herein. The features, aspects, and exemplary embodiments are susceptible to combination with one another as well as to variation and modification, as will be understood by those having skill in the art. 
     This disclosure is not limited to the disclosed exemplary embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.