A two-stage auto-cascade refrigeration system

Abstract

The present invention discloses a two-stage auto-cascade refrigeration system comprising: a high-temperature single refrigeration circuit, formed by a high-temperature compressor, a high-temperature condenser, an intermediate heat exchanger, and a high-temperature gas-liquid separator connected via refrigerant gas-liquid pipes; and a low-temperature auto-cascade circuit, formed by a low-temperature compressor, an intermediate heat exchanger, a multi-stage condenser evaporator, a multi-stage gas-liquid separator, a regenerator, and an evaporator connected via refrigerant gas-liquid pipes. The refrigerant discharged from the high-temperature compressor can undergo heat exchange with the gaseous refrigerant discharged from the low-temperature compressor within the intermediate heat exchanger to condense the low-temperature gaseous refrigerant, thereby maintaining a constant temperature of the refrigerant flowing from the intermediate heat exchanger into the multi-stage condenser evaporator. This invention solves the problems of large temperature fluctuations and poor operational stability in existing auto-cascade systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of refrigeration systems, and in particular relates to an improvement in the structure of a two-stage self-cascade refrigeration system. Background Art

[0002] Cryopreservation at -150°C is primarily used in biological and biomedical research, where it is suitable for the long-term preservation of tissues, organs, and viruses. Currently, the primary method for achieving this -150°C temperature range is through the use of a single auto-cascade refrigeration system with a mixed working fluid. While a five-stage auto-cascade refrigeration system is commonly used, it can achieve the target temperature. However, two shortcomings remain that require improvement. First, in a cascade system, the upper stage cools the lower stage, and with each additional stage, cooling efficiency decreases dramatically.

[0003] This solution has a very low COP value of the refrigeration system after five-stage cascade. If the target cooling capacity is reached, the compressor will have to do a lot of work and the instantaneous current impact at startup will be huge. Therefore, the compressor generally uses a 380V power supply, which consumes a lot of power. In addition, the ambient temperature of this single-stage self-cascade refrigeration cycle system has a greater impact on the condenser, and the temperature of the condenser directly affects the temperature of the condenser evaporator at each stage. In this way, when the ambient temperature changes, the refrigeration temperature of the entire refrigeration system will change, resulting in a large deviation in the refrigeration temperature of the refrigeration system, making the entire refrigeration system unstable and generally even unusable under high ambient temperatures. Summary of the Invention

[0004] In view of the problem that the existing condenser of the existing self-cascade system in the prior art is easily affected by the ambient temperature, resulting in deviation of the refrigeration temperature and poor operating stability, the present invention proposes a two-stage self-cascade system. The high-temperature single refrigeration circuit in the two-stage cascade cycle is a single-stage refrigeration system, which can perform heat exchange with the refrigerant discharged from the compressor in the intermediate heat exchanger and the low-temperature self-cascade circuit to ensure the relative stability of the refrigerant temperature input from the intermediate heat exchanger to the multi-stage condenser evaporator, avoid the influence of the ambient temperature, and ensure the stability of the operation of the entire refrigeration system.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0006] A two-stage auto-cascade refrigeration system, comprising:

[0007] High-temperature single refrigeration circuit: It is formed by a high-temperature compressor, a high-temperature condenser, an intermediate heat exchanger and a high-temperature gas-liquid separator connected by refrigerant gas-liquid pipes;

[0008] Low-temperature self-cascade circuit: It is formed by a low-temperature compressor, an intermediate heat exchanger, a multi-stage condenser evaporator, a multi-stage gas-liquid separator, a regenerator and an evaporator connected by refrigerant gas-liquid pipes;

[0009] Among them, the refrigerant discharged from the high-temperature compressor can exchange heat with the gaseous refrigerant discharged from the low-temperature compressor in the intermediate heat exchanger and condense the low-temperature gaseous refrigerant, so that the temperature of the refrigerant flowing from the intermediate heat exchanger into the multi-stage condensing evaporator remains constant.

[0010] In some embodiments of the present application, the low-temperature self-cascade circuit further includes:

[0011] A low-temperature oil separator, the low-temperature oil separator having an inlet, an air outlet and an oil return port, the inlet being connected to the exhaust pipe of the low-temperature compressor, the air outlet being connected to the intermediate heat exchanger through the air outlet pipe, the oil return port being connected to the suction side of the compressor through the oil return pipe, and a pre-cooling component being provided on the air outlet pipe.

[0012] In some embodiments of the present application, the multi-stage condenser evaporator is connected to its corresponding multi-stage gas-liquid separator via a refrigerant gas pipe and a refrigerant liquid pipe;

[0013] The multi-stage condenser evaporator is connected to its corresponding multi-stage gas-liquid separator through the refrigerant gas pipe and the refrigerant liquid pipe;

[0014] The multi-stage condenser evaporator includes: a first-stage condenser evaporator, a gas-liquid separator of the first-stage condenser evaporator is connected to an intermediate heat exchanger, and a return air circuit of the first-stage condenser evaporator is connected to a low-temperature compressor;

[0015] As for the remaining stages of condenser evaporators below the first stage, the corresponding gas-liquid separators of the remaining stages of condenser evaporators are connected to the condenser evaporator of the previous stage, and the return air circuits of the remaining stages of condenser evaporators are connected to the refrigerant liquid pipe of the condenser evaporator of the previous stage;

[0016] The regenerator is connected to the condenser evaporator at the end of the evaporator and the remaining stages of condenser evaporators, and its corresponding return air loop is connected to the condenser evaporator at the end.

[0017] In some embodiments of the present application, it also includes: an expansion tank, one end of the expansion tank is connected to the suction side of the low-temperature stage compressor through a first connecting pipe, and the other end of the expansion tank is connected to the refrigerant gas pipe corresponding to one of the remaining stage condenser evaporators through a second connecting pipe, a first electronic control element is provided on the first connecting pipe, and a second electronic control element is provided on the second connecting pipe.

[0018] In some embodiments of the present application, a filter element and a throttling element are provided on the refrigerant liquid pipe between each condenser evaporator and its corresponding gas-liquid separator.

[0019] In some embodiments of the present application, the multi-stage condenser evaporator is a plate condenser evaporator or a coil condenser evaporator.

[0020] In some embodiments of the present application, the refrigerant in the high-temperature single refrigeration circuit is R290, and the refrigerants in the low-temperature cascade refrigeration circuit are: R290, R1150, and R740, and their corresponding content percentages are: R290: 30%-45%, R1150: 20%-30%; R740: 20%-30%.

[0021] In some embodiments of the present application, the refrigerant in the high-temperature single refrigeration circuit is R290, and the refrigerants in the low-temperature cascade refrigeration circuit are: R290, R170, and R740, and their corresponding content percentages are: R290: 30%-45%, R170: 20%-30%; R740: 20%-30%.

[0022] In some embodiments of the present application, the refrigerant in the high-temperature single refrigeration circuit is R290, and the refrigerants in the low-temperature cascade refrigeration circuit are: R290, R1150, R740, and R50, and their corresponding content percentages are: R290: 30%-45%, R1150: 20%-30%; R740: 20%-30%, R50: 20%-30%.

[0023] In some embodiments of the present application, the refrigerant in the high-temperature single refrigeration circuit is R290, and the refrigerant in the low-temperature cascade refrigeration circuit is R290, R170, R740, and R50, and their corresponding content percentages are: R290: 30%-45%, R170: 20%-30%; R740: 20%-30%, R50: 20%-30%.

[0024] Compared with the prior art, the advantages and positive effects of the present invention are:

[0025] The two-stage auto-cascade refrigeration system proposed in the present invention includes a high-temperature single refrigeration circuit and a low-temperature auto-cascade circuit. The high-temperature single refrigeration circuit is formed by interconnecting a high-temperature compressor, a high-temperature condenser, an intermediate heat exchanger, and a high-temperature gas-liquid separator.

[0026] The low-temperature self-cascade circuit is composed of a multi-stage condenser evaporator. During the single-stage refrigeration operation of the high-temperature single refrigeration circuit, the refrigerant discharged from the low-temperature compressor in the low-temperature self-cascade circuit can be condensed through the intermediate heat exchanger to ensure that the temperature of the refrigerant input from the intermediate heat exchanger to the multi-stage condenser evaporator is relatively stable, so that the refrigerant has relatively little impact on the refrigerant temperature in the multi-stage condenser evaporator in the low-temperature self-cascade refrigeration circuit, thereby ensuring the stability of the operation of the entire refrigeration system.

[0027] And because the high-temperature refrigeration circuit is a single-stage refrigeration system, it can still maintain the corresponding refrigeration temperature in an environment with a large temperature range, thereby ensuring that the temperature of the refrigerant output from the intermediate heat exchanger is constant, so that the refrigerant output from the intermediate heat exchanger is not affected by fluctuations in ambient temperature, and has strong environmental applicability.

[0028] Other features and advantages of the present invention will become more apparent after reading the detailed description of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 This is a structural principle diagram of the two-stage auto-cascade refrigeration system of the present invention.

[0031] Among them, high temperature level single refrigeration circuit -100;

[0032] High temperature compressor-110;

[0033] High temperature condenser-120;

[0034] Intermediate heat exchanger-130;

[0035] High temperature gas-liquid separator-140;

[0036] Low temperature self-cascade circuit-200;

[0037] Low temperature compressor-210;

[0038] Low temperature oil separator-220;

[0039] First-stage gas-liquid separator-241;

[0040] First-stage condenser evaporator-242;

[0041] First stage air inlet - 2421;

[0042] First level liquid inlet-2422;

[0043] First level outlet-2423;

[0044] First level gas and liquid outlet-2424;

[0045] Primary refrigerant liquid pipe-243;

[0046] Primary refrigerant gas pipe-244;

[0047] Secondary gas-liquid separator-251;

[0048] Secondary condenser evaporator-252;

[0049] Secondary air intake - 2521;

[0050] Secondary liquid inlet-2522;

[0051] Secondary air outlet-2523;

[0052] Secondary gas and liquid outlet-2524;

[0053] Secondary refrigerant liquid pipe-253;

[0054] Secondary refrigerant gas pipe-254;

[0055] Regenerator-260;

[0056] Evaporator-270;

[0057] Return air circuit - 290;

[0058] Pre-cooling components-280;

[0059] Expansion tank-310;

[0060] First connecting pipeline-320;

[0061] Second connecting pipeline-330;

[0062] First electronic control element-340;

[0063] Second electronic control element 350;

[0064] Filter element-400;

[0065] Throttling element -500. DETAILED DESCRIPTION

[0066] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0067] It should be noted that in the description of the present invention, terms such as "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or component described must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0068] The present invention proposes an embodiment of a two-stage auto-cascade refrigeration system, referring to Figure 1 As shown, it includes a high-temperature single refrigeration circuit 100 and a low-temperature self-cascade circuit 200. The high-temperature single refrigeration circuit 100 and the low-temperature self-cascade circuit 200 are each independent and closed refrigeration cycle circuits.

[0069] The high-temperature single refrigeration circuit 100 cools down and condenses the gas refrigerant discharged from the low-temperature compressor 210 of the low-temperature self-cascade circuit 200 through an intermediate heat exchanger.

[0070] Specifically, the high-temperature single refrigeration circuit 100 in this embodiment is formed by a high-temperature compressor 110, a high-temperature condenser 120, an intermediate heat exchanger 130 and a high-temperature gas-liquid separator 140 connected to each other, and the intermediate heat exchanger 130 can be a plate heat exchanger.

[0071] In order to throttle and reduce the pressure of the refrigerant flowing out of the high-temperature condenser 120 , this embodiment also provides a high-temperature throttling capillary between the high-temperature condenser 120 and the intermediate heat exchanger 130 .

[0072] In order to prevent the refrigerant from clogging the high-temperature throttling capillary, a high-temperature filter is provided between the high-temperature condenser 120 and the high-temperature throttling capillary to filter impurities in the refrigerant and prevent the refrigerant from clogging the pipeline.

[0073] The process of the high-temperature refrigeration cycle is as follows: the high-temperature compressor 110 is running, and the gaseous refrigerant is discharged from the exhaust port of the compressor, and the refrigerant undergoes heat exchange with the air through the high-temperature condenser 120. The refrigerant changes from gas to liquid, and after throttling and pressure reduction by the high-temperature throttling capillary, it enters the intermediate heat exchanger 130, absorbs heat, and vaporizes into a gas-liquid mixture. It then passes through the high-temperature gas-liquid separator 140 for gas-liquid separation, allowing the gas to enter the compressor, completing a refrigeration cycle.

[0074] The high-temperature refrigeration cycle in this embodiment is a single refrigeration cycle, which can achieve rapid, direct and stable temperature control during operation.

[0075] The low-temperature self-cascade circuit 200 includes:

[0076] Low temperature stage compressor 210;

[0077] The multi-stage condenser evaporator includes: a first-stage condenser evaporator and other-stage condenser evaporators.

[0078] The multi-stage refrigerant evaporator is connected to its corresponding multi-stage gas-liquid separator through the refrigerant liquid pipe and the refrigerant gas pipe, and the refrigerant gas pipe and the refrigerant liquid pipe are used to realize the diversion of the refrigerant.

[0079] Among them, the gas-liquid separator of the first-stage condenser evaporator is connected to the intermediate heat exchanger 130, and the first-stage gas-liquid separator corresponding to the first-stage condenser evaporator introduces the refrigerant of the intermediate heat exchanger 130 into the first-stage condenser evaporator.

[0080] The return air loop 290 of the first-stage condenser evaporator is connected to the low-temperature stage compressor 210 to directly return the refrigerant to the low-temperature stage compressor 210.

[0081] The gas-liquid separators of the remaining stages of condenser evaporators are all connected to the upper stage condenser evaporator, and the remaining stages of condenser evaporators are used to introduce the gaseous refrigerant and liquid refrigerant in the upper stage condenser evaporator into their corresponding condenser evaporators.

[0082] The return air circuit 290 of the remaining stages of condenser evaporators is connected to the refrigerant liquid pipe of the previous stage of condenser evaporator;

[0083] The refrigerant generated in the return air circuit 290 on the remaining stages of the condenser evaporator flows into the upper stage condenser evaporator and is mixed with the refrigerant in the refrigerant liquid pipe of the upper stage condenser evaporator and then undergoes heat exchange with the refrigerant in the refrigerant gas pipe of the upper stage condenser evaporator.

[0084] The regenerator 260 is connected to the condenser evaporator at the end of the remaining stages of the condenser evaporator and the evaporator 270, and its corresponding return air loop is connected to the condenser evaporator at the end.

[0085] The refrigerant returning from the regenerator 260 flows into the condensing heat exchanger at the end to participate in heat exchange.

[0086] To achieve pressure relief, an expansion tank 310 is further provided in this embodiment. One end of the expansion tank 310 is connected to the suction side of the low-temperature stage compressor 210 through a first connecting pipe 320 .

[0087] The other end of the expansion tank 310 is connected to the refrigerant gas pipe corresponding to one of the remaining condenser evaporators through a second connecting pipe 330. A first electronic control element 340 is provided on the first connecting pipe 320, and a second electronic control element 350 is provided on the second connecting pipe 330.

[0088] The first electric control element 340 and the second electric control element 350 can be electromagnetic valves, which control the opening and closing of the first connecting pipeline 320 and the second connecting pipeline 330.

[0089] When the pressure of the refrigeration system is high, the second connecting pipe 330 can be controlled to be open by the solenoid valve, so that a part of the low-temperature gaseous refrigerant in the refrigerant pipe enters the expansion tank 310 for pressure relief.

[0090] In order to achieve the separation of gas and oil, a low-temperature oil separator 220 is correspondingly configured in this embodiment.

[0091] The low-temperature oil separator 220 has an inlet, an outlet and an oil return port. The inlet is connected to the exhaust pipe of the low-temperature compressor 210, the outlet is connected to the intermediate heat exchanger 130 through the outlet pipe, and the oil return port is connected to the suction side of the low-temperature compressor through the oil return pipe.

[0092] The refrigerant discharged from the low-temperature compressor 210 can be separated by the low-temperature oil separator 220, so that the lubricating oil enters the low-temperature compressor 210 through the return oil pipeline, and the separated gaseous refrigerant enters the intermediate heat exchanger 130 through the outlet pipeline to participate in heat exchange.

[0093] A pre-cooling component 280 is provided on the air outlet pipeline. The pre-cooling component 280 can be a micro-channel pre-cooler, which mainly realizes the pre-cooling of the refrigerant, further reduces the temperature of the refrigerant discharged from the low-temperature compressor 210, so that the two-stage self-cascade refrigeration system in this embodiment can reach a lower temperature.

[0094] In order to achieve throttling and pressure reduction of the refrigerant before it enters the condenser evaporator, in this embodiment, a throttling element 500 is provided on the refrigerant liquid pipe between each stage of the condenser evaporator and its corresponding gas-liquid separator.

[0095] In order to filter the refrigerant, a filter element 400 is further provided on the refrigerant liquid pipe between each stage of the condenser evaporator and the corresponding gas-liquid separator.

[0096] The filter element 400 is a filter, and the throttling element 500 corresponds to a throttling capillary tube.

[0097] As a preferred embodiment of the low-temperature self-cascade circuit 200 described in this embodiment, the low-temperature self-cascade circuit 200 includes two stages of condenser evaporators, both of which are plate heat exchangers. Correspondingly, the gas-liquid separator is also provided with two stages, which specifically include:

[0098] The primary gas-liquid separator 241 is connected to the intermediate heat exchanger 130 , and the primary gas-liquid separator 241 is in communication with the outlet of the intermediate heat exchanger 130 through a refrigerant pipe.

[0099] The first-level condenser evaporator 242 is connected to the first-level gas-liquid separator 241 through the first-level refrigerant liquid pipe 243 and the first-level refrigerant gas pipe 244 respectively.

[0100] Specifically, the first-level condensing evaporator 242 includes a first-level air inlet 2421, a first-level liquid inlet 2422, a first-level air outlet 2423 and a first-level gas-liquid outlet 2424. The first-level air inlet 2421 is connected to the first-level refrigerant gas pipe 244, the first-level liquid inlet 2422 is connected to the first-level refrigerant liquid pipe 243, and the first-level air outlet 2423 of the first-level condensing evaporator 242 is connected to the low-temperature compressor 210 through the return air circuit 290.

[0101] The secondary gas-liquid separator 251 is connected to the primary condenser evaporator 242 , and an inlet of the secondary gas-liquid separator 251 is connected to the primary gas-liquid outlet 2424 of the primary condenser evaporator 242 .

[0102] The secondary condenser evaporator 252 is connected to the secondary gas-liquid separator 251 via a secondary refrigerant gas pipe 254 and a secondary refrigerant liquid pipe 253 .

[0103] Specifically, the secondary condenser evaporator 252 includes a secondary air inlet 2521, a secondary liquid inlet 2522, a secondary air outlet 2523 and a secondary gas-liquid outlet 2524. The secondary air inlet 2521 is connected to the secondary refrigerant air pipe 254, the secondary liquid inlet 2522 is connected to the secondary refrigerant liquid pipe 253, and the secondary air outlet 2523 is connected to the primary refrigerant liquid pipe 243 through the return air circuit 290.

[0104] The regenerator 260 has an air inlet connected to the secondary gas-liquid outlet 2524 of the secondary condenser evaporator 252, and an air return port connected to the secondary refrigerant liquid pipe 253 through a corresponding pipeline.

[0105] The regenerator 260 includes an inner ring and an outer ring, the inner ring is provided with an air inlet, the outer ring is provided with an air return port, the secondary gas-liquid outlet 2524 of the secondary condensation evaporator 252 is connected to the air inlet of the inner ring, the outlet of the inner ring is connected to the evaporator 270, the outlet of the evaporator 270 is connected to the inlet of the outer ring of the regenerator 260, and the air return port of the outer ring is connected to the secondary refrigerant liquid pipe 253 of the secondary condensation evaporator 252.

[0106] One end of the expansion tank 310 is connected to the return air circuit 290 corresponding to the primary condenser evaporator 242 , and the other end is connected to the refrigerant gas pipe of the secondary gas-liquid separator 251 .

[0107] A filter and a throttling capillary are provided on the first-level refrigerant liquid pipe 243. The first-level gas-liquid separator 241 introduces the refrigerant flowing out of the intermediate heat exchanger 130 into the first-level condenser evaporator 242. The refrigerant first enters the first-level gas-liquid separator 241 for gas-liquid separation. The separated gas refrigerant directly enters the first-level condenser evaporator 242 through the refrigerant gas pipe. The liquid refrigerant after liquid separation is mixed with the gas refrigerant flowing into the return air circuit 290 in the second-level condenser evaporator 252 and then enters the first-level condenser evaporator 242 to exchange heat with the gaseous refrigerant in the first-level condenser evaporator 242 for further cooling. The refrigerant after heat exchange is returned to the low-temperature compressor 210 through the return air circuit 290.

[0108] The gaseous substance cooled by the first-stage condenser evaporator 242 becomes a gas-liquid mixture, and then enters the second-stage gas-liquid separator 251 for gas-liquid separation. After gas-liquid separation, the gas refrigerant cooled by heat exchange in the first-stage condenser evaporator 242 directly enters the second-stage condenser evaporator 252, while the liquid refrigerant is mixed with the low-temperature gas refrigerant returned in the return air loop 290 in the regenerator 260 and enters the second-stage condenser evaporator 252 for heat exchange with the gaseous refrigerant to further cool the gaseous refrigerant. The mixed refrigerant after heat exchange is mixed with the first-stage refrigerant liquid pipe 243 after throttling through the return air loop 290.

[0109] The cooled gas-liquid mixed refrigerant enters the inner circle of the regenerator 260. After the gaseous substance exchanges heat with the refrigerant after evaporation, it passes through the throttling element 500 and the filter element 400 and enters the evaporator 270 for evaporation to reach the target temperature. Then it enters the outer circle of the regenerator 260 to exchange heat with the liquid substance flowing out of the secondary condensation evaporator 252, and is connected to the secondary refrigerant liquid pipe 253 and mixed with the throttled refrigerant in the secondary refrigerant liquid pipe 253 to enter the secondary condensation evaporator 252 for heat exchange.

[0110] As can be seen from the above, the refrigerant entering the first-stage condenser evaporator 242 is the refrigerant that has been cooled for the first time after flowing in from the intermediate heat exchanger 130. Similarly, the refrigerant entering the second-stage condenser evaporator 252 is the refrigerant that has been further cooled after flowing out of the first-stage condenser evaporator 242. When the refrigeration system is provided with a third-stage condenser evaporator or more stages of condenser evaporators, the refrigerant entering the third-stage condenser evaporator is the refrigerant that has been cooled from the second-stage condenser evaporator 252. The refrigerant in the fourth-stage condenser evaporator and below also follows the same flow path. The refrigerant flowing out of each stage of the condenser evaporator 242 is affected by the temperature changes of the refrigerant in the previous stage.

[0111] Therefore, when the temperature of the refrigerant flowing out of the intermediate heat exchanger 130 fluctuates, the refrigerant temperature in the subsequent multi-stage condenser evaporator will cause a cumulative and increasing change in each stage. In other words, even a slight change in the refrigerant temperature in the intermediate heat exchanger 130 will cause a large fluctuation in the cooling temperature of the entire refrigeration system.

[0112] In this embodiment, a single high-temperature refrigeration circuit is provided to perform heat exchange through an intermediate heat exchanger 130 and a low-temperature self-cascade circuit, thereby ensuring that the temperature of the cooled refrigerant flowing out of the intermediate heat exchanger 130 remains basically constant, thereby avoiding the problem of large changes in the final refrigeration temperature of the entire refrigeration system, large refrigeration deviation of the refrigeration system, and unstable operation of the refrigeration system due to the unstable refrigerant temperature after the initial condensation.

[0113] At the same time, the high-temperature single refrigeration circuit in this embodiment also ensures that the temperature of the refrigerant flowing out of the intermediate heat exchanger 130 is not affected by changes in ambient temperature. The high-temperature single refrigeration circuit is a single-system cycle, which provides more stable temperature control. Furthermore, even when this system is used in different ambient temperatures, it can still maintain the refrigerant temperature output from the intermediate heat exchanger, thus avoiding the problem of the ambient temperature significantly affecting the refrigerant temperature in the intermediate heat exchanger 130.

[0114] In addition, the two-stage self-cascade refrigeration system proposed in this embodiment has the refrigeration pressure borne by the low-temperature compressor 210 and the high-temperature compressor 110 respectively. The refrigeration capacity of each compressor is much smaller than that of the compressor in a single-machine multi-stage self-cascade system. Therefore, the parameters such as the starting current of the compressor are greatly reduced, the compressor does less work, and the service life of the compressor is extended. There is no need to use a 380V power supply, and a conventional 220V power supply can be used, so that it can be plugged into the mains when in use, which is convenient to use.

[0115] In this embodiment, the two-stage auto-cascade refrigeration system not only ensures the constancy of the temperature after cascade by cooperating with the low-temperature auto-cascade circuit and the single refrigeration circuit, but also achieves an ultra-low refrigeration temperature of -150°C through multi-stage cascade refrigeration.

[0116] The first implementation method of the refrigerant in the two-stage auto-cascade refrigeration system in this embodiment is:

[0117] The refrigerant used in the high-temperature single refrigeration circuit 100 is R290, and the refrigerants in the low-temperature auto-cascade refrigeration circuit are: R290, R1150, and R740, and their content percentages are: R290: 30%-45%, R1150: 20%-30%; R740: 20%-30%.

[0118] The second implementation method of the refrigerant in the two-stage auto-cascade refrigeration system of this embodiment is:

[0119] The refrigerant in the high-temperature single refrigeration circuit 100 is R290, and the refrigerants in the low-temperature auto-cascade refrigeration circuit are: R290, R170, and R740, and their content percentages are: R290: 30%-45%, R170: 20%-30%; R740: 20%-30%.

[0120] The third implementation method of the refrigerant in the two-stage auto-cascade refrigeration system of this embodiment is:

[0121] The refrigerant in the high-temperature single refrigeration circuit 100 is R290, and the refrigerants in the low-temperature cascade refrigeration circuit are R290, R170, R740, and R50, with their content percentages being: R290: 30%-45%, R170: 20%-30%; R740: 20%-30%, and R50: 20%-30%.

[0122] The fourth implementation method of the refrigerant in the two-stage auto-cascade refrigeration system of this embodiment is:

[0123] The refrigerant in the high-temperature single refrigeration circuit 100 is R290, and the refrigerants in the low-temperature cascade refrigeration circuit are: R290, R1150, R740, and R50, with their content percentages being: R290: 30%-45%, R1150: 20%-30%, R740: 20%-30%, and R50: 20%-30%.

[0124] In this embodiment, the refrigerant of the fourth embodiment is taken as an example to illustrate the changes of the refrigerant in the circulation flow.

[0125] When the high-temperature refrigeration cycle loop is running: the high-temperature compressor 110 compresses the R290 refrigerant and then enters the high-temperature condenser 120 for cooling, turning it into a room-temperature liquid refrigerant, which is then filtered through a filter and enters the capillary flow tube for pressure reduction. It absorbs heat in the intermediate heat exchanger 130, and then performs the first cooling on the refrigerant flowing out of the low-temperature compressor 210 in the low-temperature self-cascade refrigeration circuit in the intermediate heat exchanger 130, and finally returns to the high-temperature compressor 110 after separation in the gas-liquid separator.

[0126] When the low-temperature self-cascade refrigeration circuit is in operation, the low-temperature compressor 210 compresses the refrigerant mixed with R290, R1150, R50 and R740 in the ratio of R1150: 20%-30%; R740: 20%-30%, R50: 20%-30%, and then returns the oil in the refrigerant to the low-temperature compressor 210 through the low-temperature oil separator 220, and then enters the intermediate heat exchanger 130 after passing through the pre-cooling component 280 and the filter.

[0127] The cooled gas-liquid mixture refrigerant passes through the first-stage gas-liquid separator 241 for separation, and the liquid substance R290 and part of R1150 pass through the filter and the throttling capillary and are mixed with the next-stage return air circuit 290 before entering the first-stage condenser evaporator 242. After heat exchange in the first-stage condenser evaporator 242, they return to the low-temperature compressor 210; the gaseous substance part R1150, R50 and R740 directly enter the first-stage condenser evaporator 242, become a gas-liquid mixture after cooling, and then enter the second-stage gas-liquid separator 251.

[0128] Among them, the liquid substance parts R1150 and R50 pass through the filter and the capillary flow tube and are mixed with the gas of the next-level return air circuit 290 and then enter the secondary condenser evaporator 252. After heat exchange in the secondary condenser evaporator 252, they are mixed with the refrigerant in the throttled first-level refrigerant liquid pipe 243. The gaseous substance parts R50 and R740 enter the inner circle of the regenerator 260.

[0129] After exchanging heat with the refrigerant after evaporation, it passes through the filter and is throttled by the capillary shunt pipe, and then enters the evaporator 270 to evaporate and reach the target temperature.

[0130] The two-stage auto-cascade refrigeration system proposed in this embodiment uses a mixed refrigerant of mostly hydrocarbon refrigerants and a trace amount of natural refrigerants, which does not contain halogen elements and is environmentally friendly. In addition, due to the physical properties of hydrocarbon refrigerants, it is more energy-efficient than conventional refrigerants.

[0131] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims

1. A two-stage auto-cascade refrigeration system, characterized in that: Includes: High-temperature single refrigeration circuit: It is formed by a high-temperature compressor, a high-temperature condenser, an intermediate heat exchanger and a high-temperature gas-liquid separator connected by refrigerant gas-liquid pipes; Low-temperature self-cascade circuit: It is formed by a low-temperature compressor, an intermediate heat exchanger, a multi-stage condenser evaporator, a multi-stage gas-liquid separator, a regenerator and an evaporator connected by refrigerant gas-liquid pipes; The refrigerant discharged from the high-temperature compressor can exchange heat with the gaseous refrigerant discharged from the low-temperature compressor in the intermediate heat exchanger to condense the low-temperature gaseous refrigerant, so that the temperature of the refrigerant flowing from the intermediate heat exchanger into the multi-stage condenser evaporator remains constant. The refrigerant in the high-temperature single refrigeration circuit is R290, and the refrigerants in the low-temperature cascade refrigeration circuit are: R290, R1150, and R740, and their corresponding content percentages are: R290: 30%-45%, R1150: 20%-30%; R740: 20%-30%; or, The refrigerant in the high-temperature single refrigeration circuit is R290, and the refrigerants in the low-temperature cascade refrigeration circuit are: R290, R170, and R740, and their corresponding content percentages are: R290: 30%-45%, R170: 20%-30%; R740: 20%-30%; or, The refrigerant in the high-temperature single refrigeration circuit is R290, and the refrigerants in the low-temperature cascade refrigeration circuit are: R290, R1150, R740, R50, and their corresponding content percentages are: R290: 30%-45%, R1150: 20%-30%; R740: 20%-30%, R50: 20%-30%; or, The refrigerant in the high-temperature single refrigeration circuit is R290, and the refrigerant in the low-temperature cascade refrigeration circuit is R290, R170, R740, and R50. The corresponding content percentages are: R290: 30%-45%, R170: 20%-30%; R740: 20%-30%, R50: 20%-30%; The multi-stage condenser evaporator is connected to its corresponding multi-stage gas-liquid separator through the refrigerant gas pipe and the refrigerant liquid pipe; The multi-stage condenser evaporator includes: a first-stage condenser evaporator, a first-stage gas-liquid separator of the first-stage condenser evaporator is connected to an intermediate heat exchanger, and a return air circuit of the first-stage condenser evaporator is connected to a low-temperature stage compressor; As for the remaining stages of condenser evaporators below the first stage, the corresponding gas-liquid separators of the remaining stages of condenser evaporators are connected to the condenser evaporator of the previous stage, and the return air circuits of the remaining stages of condenser evaporators are connected to the refrigerant liquid pipe of the condenser evaporator of the previous stage; The regenerator is connected to the evaporator and the condenser evaporator at the end of the remaining stages, and its corresponding return air loop is connected to the condenser evaporator at the end; The first-stage gas-liquid separator introduces the refrigerant from the intermediate heat exchanger into the first-stage condenser evaporator; The return air loop of the first-stage condenser evaporator is connected to the low-temperature compressor to directly return the refrigerant to the low-temperature compressor; The gas-liquid separators of the remaining stages of condenser evaporators are all connected to the upper stage condenser evaporator, and the remaining stages of condenser evaporators are used to introduce the gaseous refrigerant and liquid refrigerant in the upper stage condenser evaporator into the corresponding condenser evaporator; The return air circuits of the remaining stages of condenser evaporators are connected to the refrigerant liquid pipes of the upper stage condenser evaporators; the refrigerant generated in the return air circuits on the remaining stages of condenser evaporators flows into the upper stage condenser evaporator and is mixed with the refrigerant in the refrigerant liquid pipe of the upper stage condenser evaporator, and then undergoes heat exchange with the refrigerant in the refrigerant gas pipe of the upper stage condenser evaporator.

2. The two-stage auto-cascade refrigeration system according to claim 1, characterized in that: The low-temperature self-cascade circuit also includes: A low-temperature oil separator, the low-temperature oil separator having an inlet, an air outlet and an oil return port, the inlet being connected to the exhaust pipe of the low-temperature compressor, the air outlet being connected to the intermediate heat exchanger through the air outlet pipe, the oil return port being connected to the suction side of the compressor through the oil return pipe, and a pre-cooling component being provided on the air outlet pipe.

3. The two-stage auto-cascade refrigeration system according to claim 2, characterized in that: It also includes: an expansion tank, one end of the expansion tank is connected to the suction side of the low-temperature stage compressor through a first connecting pipe, and the other end of the expansion tank is connected to the refrigerant gas pipe corresponding to one of the remaining stage condensing evaporators through a second connecting pipe, a first electronic control element is provided on the first connecting pipe, and a second electronic control element is provided on the second connecting pipe.

4. The two-stage auto-cascade refrigeration system according to claim 1, characterized in that: A filter element and a throttling element are provided on the refrigerant liquid pipe between each condenser evaporator and its corresponding gas-liquid separator.

5. The two-stage auto-cascade refrigeration system according to claim 1, characterized in that: The multi-stage condenser evaporator is a plate heat exchanger or a coil heat exchanger.

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