Cascade refrigeration system and refrigeration device

Abstract

This application relates to a cascade refrigeration system and refrigeration equipment, belonging to the field of refrigeration technology, and aims to improve the refrigeration response speed of the low-temperature refrigeration circuit of the cascade refrigeration system upon startup. The cascade refrigeration system includes an intermediate heat exchanger, a high-temperature refrigeration circuit, a low-temperature refrigeration circuit, and a bypass circuit. The high-temperature refrigeration circuit includes a first compressor, a first condenser, a first expansion valve, and an intermediate heat exchanger connected in sequence, with the intermediate heat exchanger serving as the evaporator side in the high-temperature refrigeration circuit. The low-temperature refrigeration circuit includes a second compressor, an intermediate heat exchanger, a second expansion valve, and an evaporator connected in sequence, with the intermediate heat exchanger serving as the condenser side in the low-temperature refrigeration circuit. The bypass circuit is disposed within the low-temperature refrigeration circuit. The bypass circuit includes a circulation pump and is configured such that: before the second compressor starts, the high-temperature refrigeration circuit starts, and the bypass circuit is activated for a first preset time to drive the refrigerant to circulate along the low-temperature refrigeration circuit.

Description

Technical Field

[0001] This application relates to the field of refrigeration technology, and in particular to a dehumidifying air conditioner and its control method. Background Technology

[0002] Biological samples, pharmaceuticals, and vaccines require low temperatures for preservation. Therefore, refrigeration systems often employ a cascade structure, using two separate refrigeration systems—a high-temperature stage and a low-temperature stage—to achieve a more efficient low-temperature environment.

[0003] Cascade refrigeration systems typically start the high-temperature refrigeration cycle first, followed by the low-temperature refrigeration cycle. During the startup of the low-temperature refrigeration cycle, due to the low subcooling of the low-temperature refrigerant in the intermediate heat exchanger, some of the refrigerant is depressurized and vaporized before passing through the evaporator as it flows towards the evaporator under the compressor's drive. This results in lower heat exchange efficiency for the gaseous refrigerant as it flows through the evaporator, and the smaller refrigerant flow rate leads to a slower temperature drop. Utility Model Content

[0004] This application provides a cascade refrigeration system and refrigeration equipment, which aims to improve the refrigeration response speed of the low-temperature refrigeration circuit when the cascade refrigeration system is started.

[0005] In a first aspect, embodiments of this application provide a cascade refrigeration system, including an intermediate heat exchanger, a high-temperature refrigeration circuit, a low-temperature refrigeration circuit, and a bypass circuit. The high-temperature refrigeration circuit includes a first compressor, a first condenser, a first expansion valve, and an intermediate heat exchanger connected in sequence, with the intermediate heat exchanger serving as the evaporator side in the high-temperature refrigeration circuit. The low-temperature refrigeration circuit includes a second compressor, an intermediate heat exchanger, a second expansion valve, and an evaporator connected in sequence, with the intermediate heat exchanger serving as the condenser side in the low-temperature refrigeration circuit. The bypass circuit is disposed within the low-temperature refrigeration circuit. The bypass circuit includes a circulation pump and is configured such that: before the second compressor starts, the high-temperature refrigeration circuit starts, and the bypass circuit is activated for a first preset time to drive the refrigerant to circulate along the low-temperature refrigeration circuit.

[0006] In some implementations, a bypass circuit is connected in parallel between the second compressor and the intermediate heat exchanger.

[0007] In some implementations, the bypass loop is connected in parallel between the intermediate heat exchanger and the second throttle.

[0008] In some implementations, the bypass circuit includes a bypass valve connected in series with the circulation pump. The bypass valve is a check valve or an electrically controlled valve. The check valve is configured to prevent refrigerant from flowing backwards in the bypass circuit, and the circulation pump starts to open the bypass circuit. The electrically controlled valve opens, and the circulation pump starts to open the bypass circuit.

[0009] In some embodiments, a bypass circuit is provided between the second compressor and the intermediate heat exchanger. The cryogenic refrigeration circuit includes a second filter connected upstream of the intermediate heat exchanger, and the two ends of the bypass circuit are connected in parallel with the two ends of the second filter.

[0010] In some embodiments, the cryogenic refrigeration circuit further includes a second condenser and a liquid receiver. The second condenser is disposed between the second compressor and the intermediate heat exchanger. The liquid receiver is connected between the second condenser and the intermediate heat exchanger, and a bypass circuit is disposed downstream of the liquid receiver.

[0011] In some embodiments, the cascade refrigeration system further includes a condenser fan, with the second condenser and the first condenser located on the same side or opposite sides of the condenser fan.

[0012] In some embodiments, the cryogenic refrigeration circuit includes a pressure relief valve, a second expansion valve, and an evaporator connected in parallel with the pressure relief valve. The opening degree of the pressure relief valve in the open state is greater than the opening degree of the second expansion valve. The pressure relief valve is configured to open for a third preset time before the second compressor starts, with the second preset time being 0.1s-0.5s and the third preset time being longer than the second preset time.

[0013] In some implementations, the cryogenic refrigeration circuit also includes an expansion tank and an expansion valve, with one end of the expansion valve connected to the expansion tank and the other end of the expansion valve connected to the end of the pressure relief valve away from the intermediate heat exchanger.

[0014] In some embodiments, the expansion valve is configured to open synchronously with the pressure relief valve, and the expansion valve closes after a fourth preset time, the fourth preset time being longer than a third preset time.

[0015] In some embodiments, the cascade refrigeration system further includes a main control module, a pressure sensor, a first temperature sensor, and a second temperature sensor. The pressure sensor is located in the low-temperature refrigeration circuit and is used to detect the pressure parameter between the second compressor and the second expansion joint. The first temperature sensor is located in the intermediate heat exchanger and is used to detect the evaporator-side temperature of the intermediate heat exchanger. The second temperature sensor is located in the intermediate heat exchanger and is used to detect the condenser-side temperature of the intermediate heat exchanger. The main control module is electrically connected to the pressure sensor, the first temperature sensor, and the second temperature sensor, and is used to adjust the operating status of the low-temperature refrigeration circuit and the high-temperature refrigeration circuit.

[0016] Secondly, this application provides a refrigeration device, including the cascade refrigeration system described in the first aspect.

[0017] The technical solutions provided in this application have the following advantages compared with the prior art: In the high-temperature refrigeration circuit, the refrigerant (i.e., the first refrigerant) is compressed by the first compressor and flows sequentially from its outlet through the first condenser, the first expansion valve, the intermediate heat exchanger, and the return port of the first compressor. Thus, the compressed first refrigerant liquefies and releases heat as it flows through the first condenser, allowing it to dissipate heat quickly and improving its heat release and liquefaction efficiency. The liquefied first refrigerant then absorbs heat and vaporizes after flowing into the intermediate heat exchanger through the first expansion valve. This designates the side of the intermediate heat exchanger connected to the high-temperature refrigeration circuit as the evaporation side, used to cool the side connected to the low-temperature refrigeration circuit (i.e., the condensation side).

[0018] In the low-temperature refrigeration circuit, the refrigerant (i.e., the second refrigerant) is compressed by the second compressor and flows sequentially from its outlet through the intermediate heat exchanger, the second expansion valve, the evaporator, and the return port of the second compressor. Thus, the compressed second refrigerant, while flowing through the intermediate heat exchanger, is fully heated and liquefied by the evaporator side (i.e., the first refrigerant in the high-temperature refrigeration circuit), resulting in high liquefaction efficiency and degree of liquefaction at the intermediate heat exchanger. The liquefied second refrigerant then flows through the second expansion valve into the evaporator, where it absorbs heat and vaporizes for cooling.

[0019] By incorporating a bypass circuit in the low-temperature refrigeration circuit, the bypass circuit can drive the second refrigerant to circulate before the second compressor starts. Thus, by starting the high-temperature refrigeration circuit and the circulating pump, the second refrigerant, while circulating within the low-temperature refrigeration circuit, can exchange heat with the first refrigerant through an intermediate heat exchanger, thereby lowering the temperature of the second refrigerant. This circulation process continues for a first preset time, causing the temperature of the second refrigerant to fall below its saturation temperature.

[0020] Thus, when the bypass circuit is closed to start the second compressor, the second refrigerant flows from the intermediate heat exchanger through the second expansion valve to the evaporator. Because the second refrigerant is below its saturation temperature, even after the pressure drop through the second expansion valve, the second refrigerant with its higher subcooling will not undergo phase change vaporization before flowing through the evaporator. This allows the second refrigerant to fully absorb heat and vaporize in the evaporator, thereby achieving better low-temperature cooling effect and higher cooling efficiency, and enabling the low-temperature refrigeration circuit to quickly respond to cooling demands after startup. Attached Figure Description The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0023] Figure 1 This is a schematic diagram of the connection structure of a cascade refrigeration system provided in an embodiment of this application; Figure 2 A schematic diagram of the electrical connections of electrical components in a cascade refrigeration system provided in an embodiment of this application; Figure 3 This is a schematic diagram of the connection structure of another cascade refrigeration system provided in an embodiment of this application; Figure 4 for Figure 3 A schematic diagram of a connection structure between the high-temperature refrigeration circuit and the intermediate heat exchanger shown in the figure; Figure 5 for Figure 3 A schematic diagram of a connection structure for the cryogenic refrigeration circuit, intermediate heat exchanger, and bypass circuit shown in the figure; Figure 6 A flowchart of a control method for a cascade refrigeration system provided in an embodiment of this application; Figure 7 This is a schematic diagram of the connection structure of a main control module provided in an embodiment of this application.

[0024] Explanation of reference numerals in the attached figures: 100. High-temperature refrigeration circuit; 110. First compressor; 120. First condenser; 130. First throttling device; 140. First gas-liquid separator; 150. First filter; 160. Anti-condensation pipe; 200. Low-temperature refrigeration circuit; 210. Second compressor; 220. Second throttle; 230. Evaporator; 241. Second filter; 242. Oil separator; 251. Second condenser; 252. Liquid receiver; 261. Pressure relief valve; 262. Expansion tank; 263. Expansion valve; 300. Intermediate heat exchanger; 400. Bypass circuit; 410. Circulating pump; 420. Bypass valve; 500. Condensing fan; 610. Main control module; 611. Processor; 612. Communication interface; 613. Memory; 614. Communication bus; 620. Pressure sensor; 630. First temperature sensor; 640. Second temperature sensor. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] The following disclosure provides numerous different embodiments or examples for implementing various structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0027] For ease of description, spatial relative terms may be used in the text to describe the relative position or movement of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "front," "back," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure undergoes a positional flip, orientation change, or change of motion, these directional indications will change accordingly. For instance, an element described as "below other elements or features" or "below other elements or features" will subsequently be oriented "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions), and the spatial relative descriptors used in the text will be interpreted accordingly.

[0028] Figure 1 This is a schematic diagram of the connection structure of a cascade refrigeration system provided in an embodiment of this application. Figure 2 This is a schematic diagram of the electrical connections of electrical components in a cascade refrigeration system provided in an embodiment of this application. Figure 3 This is a schematic diagram of the connection structure of another cascade refrigeration system provided in an embodiment of this application. Figure 4 for Figure 3 The diagram shows a connection structure between the high-temperature refrigeration circuit and the intermediate heat exchanger. Figure 5 for Figure 3 The diagram shows a connection structure of the cryogenic refrigeration circuit, intermediate heat exchanger, and bypass circuit shown. Figure 6 A flowchart illustrating a control method for a cascade refrigeration system provided in this application embodiment. Figure 7 This is a schematic diagram of the connection structure of a main control module provided in an embodiment of this application.

[0029] Please see Figures 1 to 7 This application provides a cascade refrigeration system and refrigeration equipment, which aims to improve the refrigeration response speed of the low-temperature refrigeration circuit when the cascade refrigeration system is started.

[0030] Firstly, such as Figure 1 As shown, this application embodiment provides a cascade refrigeration system, including a high-temperature refrigeration circuit 100, a low-temperature refrigeration circuit 200, an intermediate heat exchanger 300, and a bypass circuit 400. The high-temperature refrigeration circuit 100 includes a first compressor 110, a first condenser 120, a first throttling device 130, and an intermediate heat exchanger 300 connected in sequence, with the intermediate heat exchanger 300 serving as the evaporator side in the high-temperature refrigeration circuit 100. The low-temperature refrigeration circuit 200 includes a second compressor 210, an intermediate heat exchanger 300, a second throttling device 220, and an evaporator 230 connected in sequence, with the intermediate heat exchanger 300 serving as the condenser side in the low-temperature refrigeration circuit 200. The bypass circuit 400 is disposed within the low-temperature refrigeration circuit 200 and includes a circulation pump 410. The bypass circuit 400 is configured such that: before the second compressor 210 starts, the high-temperature refrigeration circuit 100 starts, and the bypass circuit 400 is activated for a first preset time t1 to drive the refrigerant to circulate along the low-temperature refrigeration circuit 200.

[0031] The first throttle 130 and the second throttle 220 can be corresponding capillary tubes or electronic throttle valves with adjustable opening, etc., and there is no limitation on them.

[0032] In the high-temperature refrigeration circuit 100, the refrigerant (i.e., the first refrigerant) is compressed by the first compressor 110 and flows sequentially from its outlet through the first condenser 120, the first expansion valve 130, the intermediate heat exchanger 300, and the return port of the first compressor 110. Thus, the compressed first refrigerant liquefies and releases heat as it flows through the first condenser 120, allowing it to dissipate heat quickly and improving its heat release and liquefaction efficiency. The liquefied first refrigerant absorbs heat and vaporizes after flowing into the intermediate heat exchanger 300 through the first expansion valve 130, making the side of the intermediate heat exchanger 300 connected to the high-temperature refrigeration circuit 100 the evaporation side, used to cool the side of the intermediate heat exchanger 300 connected to the low-temperature refrigeration circuit 200 (i.e., the condensation side).

[0033] In the low-temperature refrigeration circuit 200, the refrigerant (i.e., the second refrigerant) is compressed by the second compressor 210 and flows sequentially from its outlet through the intermediate heat exchanger 300, the second expansion valve 220, the evaporator 230, and the return port of the second compressor 210. Thus, the compressed second refrigerant, while flowing through the intermediate heat exchanger 300, is fully heated and liquefied by the evaporator side (i.e., the first refrigerant in the high-temperature refrigeration circuit 100), resulting in high liquefaction efficiency and degree of liquefaction at the intermediate heat exchanger 300. The liquefied second refrigerant then flows through the second expansion valve 220 into the evaporator 230, where it absorbs heat and vaporizes for cooling.

[0034] The intermediate heat exchanger 300 has two mutually isolated heat exchange chambers, allowing the first and second refrigerants to flow and exchange heat within these chambers. A large isolation area exists between the two chambers to increase the heat exchange area between the first and second refrigerants. The intermediate heat exchanger 300 can be a plate heat exchanger or a shell-and-tube heat exchanger, achieving heat exchange between the first and second refrigerants through a dual-channel design.

[0035] In this way, the second refrigerant can liquefy and release heat within the intermediate heat exchanger 300, while the first refrigerant can absorb heat and vaporize within the intermediate heat exchanger 300. Through the phase change heat absorption of the first refrigerant, the second refrigerant can fully release heat to improve liquefaction efficiency and degree. This results in the second refrigerant flowing out of the intermediate heat exchanger 300 having a higher degree of subcooling, thereby absorbing heat at the evaporator 230 through vaporization of the second refrigerant to lower the ambient temperature.

[0036] Based on this, the second refrigerant can be a low-temperature refrigerant such as R23, R14, or R508B, with an evaporation temperature on the evaporator side reaching -50℃ to -120℃ and a condensation temperature on the condenser side reaching -20℃ to -40℃. By absorbing heat through the evaporation of the second refrigerant, a lower cooling temperature is formed at the evaporator 230, allowing the ambient temperature to be reduced to below -50℃ or -80℃, resulting in good low-temperature cooling performance.

[0037] Since the condensation temperature of the second refrigerant can reach -20℃ to -40℃, which is far lower than the ambient temperature, a high-temperature refrigeration circuit 100 can be set up and high-temperature refrigerants such as R404A, R410A, or R22 can be used to ensure that the second refrigerant can be fully liquefied and release heat before flowing through the evaporator 230. Because the evaporation temperature of this high-temperature refrigerant is -20℃ to -40℃, its condensation temperature on the condensing side is approximately the ambient temperature. In this way, in the high-temperature refrigeration circuit 100, the compressed first refrigerant can fully release heat and liquefy at the first condenser 120. When the liquefied first refrigerant flows through the intermediate heat exchanger 300, since the evaporation temperature of the first refrigerant is close to the condensation temperature range of the second refrigerant, the liquid first refrigerant and the gaseous second refrigerant can fully exchange heat through the intermediate heat exchanger, thereby improving the liquefaction efficiency and degree of liquefaction of the second refrigerant. This results in the low-temperature refrigeration circuit 200 having a better low-temperature refrigeration effect at the evaporator.

[0038] When a cascade refrigeration system starts, the high-temperature refrigeration circuit 100 must be activated first, followed by the low-temperature refrigeration circuit 200. Because the second refrigerant in the low-temperature refrigeration circuit 200 cannot be sufficiently cooled before startup, its temperature is relatively high. When the second compressor 210 starts to drive the second refrigerant from the intermediate heat exchanger 300 to the evaporator 230, the insufficiently subcooled second refrigerant will vaporize as it flows through the evaporator 230. This results in a large amount of gaseous refrigerant flowing through the evaporator 230, but it cannot absorb heat for cooling through the vaporization phase change process of the second refrigerant, thus significantly reducing the cooling efficiency and effect at the evaporator 230. In other words, the low-temperature refrigeration circuit 200 has a slow cooling response speed after startup.

[0039] Based on this, a bypass circuit 400 is provided in the low-temperature refrigeration circuit 200 so that the bypass circuit 400 can drive the second refrigerant to circulate before the second compressor 210 starts via the circulation pump 410. Thus, by starting the high-temperature refrigeration circuit 100 and the circulation pump 410, the second refrigerant, during its circulation within the low-temperature refrigeration circuit 200, can exchange heat with the first refrigerant through the intermediate heat exchanger 300, thereby lowering the temperature of the second refrigerant. After this circulation process continues for a first preset time t1, the temperature of the second refrigerant is reduced below its saturation temperature.

[0040] Thus, when the bypass circuit 400 is closed to start the second compressor 210, the second refrigerant flows from the intermediate heat exchanger 300 through the second expansion valve 220 to the evaporator 230. Because the second refrigerant is below its saturation temperature, even after the pressure drop through the second expansion valve 220, the second refrigerant with a higher degree of subcooling will not undergo phase change vaporization before flowing through the evaporator 230. This allows the second refrigerant to fully absorb heat and vaporize in the evaporator 230, thereby achieving a better low-temperature cooling effect and higher cooling efficiency, and enabling the low-temperature refrigeration circuit 200 to quickly respond to cooling demands after startup.

[0041] It should be noted that before the second compressor 210 of the low-temperature refrigeration circuit 200 starts, the start-up time of the bypass circuit 400 can be determined by a preset time or by whether the temperature of the second refrigerant in the intermediate heat exchanger 300 is lower than the saturation temperature.

[0042] For example, the effective conduction time of the bypass circuit 400, i.e., the first preset time t1, can be verified by experiment. This is to ensure that after the bypass circuit 400 and the high-temperature refrigeration circuit 100 are started for the first preset time t1, the temperature of the second refrigerant flowing out of the intermediate heat exchanger 300 is lower than the saturation temperature at the current pressure, and there is a large temperature difference between the temperature of the second refrigerant and the saturation temperature, so that the second refrigerant has a high degree of subcooling, thereby avoiding the occurrence of phase change vaporization of the second refrigerant due to a sudden drop in pressure before entering the evaporator 230.

[0043] The first preset time t1 can be 3-5 minutes. For example, the first preset time t1 can be three minutes, four minutes, or five minutes.

[0044] In some embodiments, such as Figure 2 and Figure 3 As shown, the cascade refrigeration system also includes a main control module 610, a pressure sensor 620, a first temperature sensor 630, and a second temperature sensor 640. The main control module 610 is electrically connected to the pressure sensor 620, the first temperature sensor 630, and the second temperature sensor 640, and is used to regulate the operating status of the low-temperature refrigeration circuit 200 and the high-temperature refrigeration circuit 100.

[0045] A pressure sensor 620 is installed in the low-temperature refrigeration circuit 200 to detect the pressure parameters between the second compressor 210 and the second throttle 220. A first temperature sensor 630 is installed in the intermediate heat exchanger 300 to detect the evaporator-side temperature of the intermediate heat exchanger 300, i.e., the evaporation temperature of the high-temperature refrigeration circuit 100 at the intermediate heat exchanger 300, or the outlet temperature of the intermediate heat exchanger 300 at the outlet of the first refrigerant. A second temperature sensor 640 is installed in the intermediate heat exchanger 300 to detect the condenser-side temperature of the intermediate heat exchanger 300, i.e., the condensation temperature of the low-temperature refrigeration circuit 200 at the intermediate heat exchanger 300, or the outlet temperature of the intermediate heat exchanger 300 at the outlet of the second refrigerant.

[0046] like Figure 2 As shown, the main control module 610 is also electrically connected to the second compressor 210, the first compressor 110, and the circulating pump 410. At this time, the main control module 610 can control the first compressor 110 to remain running, and the main control module 610 controls the circulating pump 410 to shut down and start the first compressor 110, thereby controlling the start of the low-temperature refrigeration circuit 200.

[0047] Thus, when the high-temperature refrigeration circuit 100 and the bypass circuit 400 are connected, the main control module 610 can detect the first temperature on the evaporator side and the second temperature on the condenser side in the intermediate heat exchanger 300. The main control module 610 can also detect the pressure parameters upstream of the second throttle 220 in the low-temperature refrigeration circuit 200. This allows the main control module 610 to obtain the saturation temperature of the second refrigerant under the current pressure parameters based on the type of the second refrigerant and the preset curve. Furthermore, it determines whether the second refrigerant has reached the preset subcooling degree based on whether the difference between the saturation temperature and the second temperature is greater than a preset value.

[0048] If so, the main control module 610 controls the circulation pump 410 to shut down and starts the first compressor 110, thereby controlling the start of the low-temperature refrigeration circuit 200. At this time, the start time of the circulation pump 410 can be regarded as the first preset time t1.

[0049] The bypass circuit 400 can be connected in series with the cryogenic refrigeration circuit 200.

[0050] However, in order to reduce the flow resistance of the cryogenic refrigeration circuit 200 when the bypass circuit 400 is closed, such as... Figure 1 and Figure 3 As shown, the bypass circuit 400 is connected in parallel between the second compressor 210 and the intermediate heat exchanger 300. Alternatively, the bypass circuit 400 is connected in parallel between the intermediate heat exchanger 300 and the second throttle 220.

[0051] Two refrigerant pipes are connected in parallel between the second compressor 210 and the intermediate heat exchanger 300, one of which is a bypass circuit 400. Alternatively, two refrigerant pipes are connected in parallel between the intermediate heat exchanger 300 and the second throttle 220, one of which is a bypass circuit 400.

[0052] Thus, when the bypass circuit 400 is closed, the second refrigerant can circulate through another refrigerant pipe, and the installation of the circulation pump 410 will not increase the flow resistance in the low-temperature refrigeration circuit 200. This is beneficial for improving the circulation speed of the second refrigerant and the overall system energy efficiency ratio.

[0053] like Figure 1 and Figure 3 As shown, the bypass circuit 400 also includes a bypass valve 420 connected in series with the circulation pump 410. The bypass valve 420 may be an electrically controlled valve, which opens and the circulation pump 410 starts to make the bypass circuit 400 open.

[0054] like Figure 2 As shown, the main control module 610 is electrically connected to the bypass valve 420. This allows the main control module 610 to control the bypass valve 420 to open and start the circulation pump 410, thus ensuring the bypass circuit 400 is open. Alternatively, the main control module 610 can control the circulation pump 410 and the bypass valve 420 to disconnect the bypass circuit 400, preventing the second refrigerant from flowing through the bypass circuit 400 and interfering with the circulation of the second refrigerant after the low-temperature refrigeration circuit 200 is started.

[0055] Alternatively, the bypass valve 420 can be configured as a one-way valve. In this case, the one-way valve can be set to prevent the second refrigerant from flowing backward in the bypass circuit 400, so that the main control module 610 can control the circulation pump 410 to start and open the bypass circuit 400.

[0056] With the circulating pump 410 off and the cryogenic refrigeration circuit 200 started, some of the second refrigerant can flow from the second compressor 210 to the second expansion valve 220 via the bypass circuit 400. However, the one-way valve prevents the refrigerant from flowing in the opposite direction from the second compressor 210 via the bypass circuit 400 to the second expansion valve 220. This does not affect the circulation of the second refrigerant in the cryogenic refrigeration circuit 200.

[0057] In some embodiments, such as Figure 1 As shown, the bypass circuit 400 is disposed between the second compressor 210 and the intermediate heat exchanger 300. The cryogenic refrigeration circuit 200 includes a second filter 241 connected upstream of the intermediate heat exchanger 300, and the two ends of the bypass circuit 400 are connected in parallel with the two ends of the second filter 241.

[0058] The second filter 241 refers to a device used to remove impurities and moisture from the second refrigerant. The second filter 241 may be a tank structure including a built-in molecular sieve or activated carbon. By setting the second filter 241 upstream of the intermediate heat exchanger 300, moisture and impurities can be prevented from entering the interior of the intermediate heat exchanger 300, thereby affecting the contact heat exchange effect between the subsequent refrigerant and the intermediate heat exchanger 300 or the evaporator 230.

[0059] By connecting a bypass circuit 400 in parallel across the two ends of the second filter 241, the second refrigerant can circulate through the second filter 241 after the second compressor 210 starts, and circulate through the bypass circuit 400 before the second compressor 210 starts, so as to avoid the filter adsorption resistance of the second filter 241 affecting the smooth flow of the second refrigerant.

[0060] For example, before the second compressor 210 starts, the high-temperature refrigeration circuit 100 starts first, at which time the bypass circuit 400 is open. The circulation pump 410 drives the second refrigerant in the low-temperature refrigeration circuit 200 to flow through the bypass circuit 400, forming a circulation path that does not pass through the second filter 241. This design allows the second refrigerant to flow with low resistance and sufficient volume before the second compressor 210 starts, preventing the accumulation of liquid second refrigerant in the intermediate heat exchanger 300 and avoiding insufficient subcooling of the second refrigerant.

[0061] After the system has run for a first preset time t1, the bypass circuit 400 is closed, and the second refrigerant resumes its normal flow path through the second filter 241 under the drive of the second compressor 210. The parallel structure of the second filter 241 and the bypass circuit 400 can prevent impurities from entering the intermediate heat exchanger 300 during the circulation phase of the low-temperature refrigeration circuit 200, while also avoiding significant resistance in the second filter 241 when the second refrigerant is flowing under the influence of the circulating pump 410.

[0062] The parallel connection of the bypass circuit 400 and the second filter 241 ensures sufficient circulation of the second refrigerant during the precooling stage, reducing the amount of liquid refrigerant retained in the intermediate heat exchanger 300. Simultaneously, this structure prevents the second filter 241 from becoming a source of flow resistance during system startup, reducing the delayed start-up time of the second compressor 210. After the bypass precooling stage, the second filter 241 functions normally in the low-temperature refrigeration circuit 200, ensuring the purity of the second refrigerant during long-term operation.

[0063] In some embodiments, such as Figure 3 and Figure 5 As shown, the low-temperature refrigeration circuit 200 also includes a second condenser 251. The second condenser 251 is disposed between the second compressor 210 and the intermediate heat exchanger 300.

[0064] The second condenser 251 is a heat exchange device used for preliminary cooling of the high-temperature gaseous second refrigerant discharged from the second compressor 210 in the low-temperature refrigeration circuit 200. It can be implemented using a finned tube heat exchanger or a shell-and-tube heat exchanger. By placing the second condenser 251 upstream of the intermediate heat exchanger 300, the high-temperature gaseous second refrigerant can exchange heat with the external environment through the second condenser 251. Then, the intermediate heat exchanger 300 performs a secondary heat exchange with the first refrigerant in the high-temperature refrigeration circuit 100, which helps improve the liquefaction heat release effect of the second refrigerant.

[0065] like Figure 3 and Figure 5 As shown, the low-temperature refrigeration circuit 200 also includes a liquid receiver 252, which is connected between the second condenser 251 and the intermediate heat exchanger 300. The bypass circuit 400 is located downstream of the liquid receiver 252.

[0066] The receiver 252 is a container used to store liquid second refrigerant to regulate the flow rate of the second refrigerant in the low-temperature refrigeration circuit 200. For example, a vertical storage tank with gas-liquid separation function can be used as the receiver 252 to buffer fluctuations in the flow rate of the second refrigerant.

[0067] Based on this, the bypass circuit 400 is located downstream of the liquid receiver 252, so that the inlet and outlet of the circulation pump 410 are respectively connected between the outlet end of the liquid receiver 252 and the inlet end of the intermediate heat exchanger 300. In this way, within the first preset time t1 before the second compressor 210 starts, the circulation pump 410 can draw liquid or gaseous second refrigerant from the liquid receiver 252 and the second condenser 251 and quickly flow it through the intermediate heat exchanger 300, so that the second refrigerant can exchange heat with the first refrigerant in the high-temperature refrigeration circuit 100 in the intermediate heat exchanger 300 to fully liquefy and cool down, so that the second refrigerant flowing out of the intermediate heat exchanger 300 has a high degree of subcooling, which facilitates the second compressor 210 to start up, so that the low-temperature refrigeration circuit 200 can respond stably and quickly to the refrigeration effect.

[0068] Traditional cascade refrigeration systems often suffer from uneven refrigerant distribution in the intermediate heat exchanger 300 due to the lack of a buffer in the receiver 252 and forced circulation in the bypass circuit 400 before the second compressor 210 starts. This solution addresses this by adding a second condenser 251 to lower the refrigerant temperature, using the receiver 252 to balance the flow fluctuations of the second refrigerant, and placing the bypass circuit 400 downstream of the receiver 252. This allows the second refrigerant to quickly establish a stable flow path for cooling when the second compressor 210 starts, preventing excessive accumulation of liquid refrigerant in the intermediate heat exchanger.

[0069] The first condenser 120 and the second condenser 251 can be set in different positions so that the refrigerant flowing through the condenser can quickly exchange heat with the ambient space under the drive of the fan.

[0070] Or, such as Figure 3 and 4 As shown, the cascade refrigeration system also includes a condenser fan 500, with the second condenser 251 and the first condenser 120 disposed on the same side or opposite sides of the condenser fan 500. That is, by sequentially arranging the first condenser 120 and the second condenser 251 on one side of the condenser fan 500, or sequentially arranging the first condenser 120 and the second condenser 251 on opposite sides of the condenser fan 500, the first condenser 120 and the second condenser 251 can be centrally arranged in the same spatial location, which is beneficial for the integration and miniaturization of the cascade refrigeration system.

[0071] It should be noted that, although the condensation temperature range of the second refrigerant is usually lower than the ambient temperature, the condensation temperature range of the second refrigerant is adjacent to the evaporation temperature range of the first refrigerant. That is, the second refrigerant can be pre-cooled by the second condenser 251 so that the second refrigerant can fully release heat and liquefy in the intermediate heat exchanger 300.

[0072] Among them, such as Figure 3 and Figure 4 As shown, in the high-temperature refrigeration circuit 100, a first gas-liquid separator 140 is connected between the intermediate heat exchanger 300 and the first compressor 110 to filter the liquid phase and moisture in the gaseous refrigerant flowing to the first compressor 110, so as to avoid liquid slugging.

[0073] Continue to refer to Figure 4 A first filter 150 is connected between the first throttle 130 and the first condenser 120, that is, downstream of the first condenser 120, to filter the first refrigerant flowing into the intermediate heat exchanger 300 to remove water and impurities, thereby preventing moisture or impurities from affecting the heat exchange efficiency of the first refrigerant in the intermediate heat exchanger 300, which is beneficial to improving the overall low-temperature refrigeration efficiency of the system and improving the low-temperature refrigeration effect.

[0074] In some embodiments, such as Figure 3 and Figure 4As shown, the high-temperature refrigeration circuit 100 also includes an anti-condensation pipe 160, which connects the first compressor 110 and the first condenser 120. Spatially, the anti-condensation pipe 160 is positioned around the enclosure (e.g., a low-temperature refrigerator). Since the high-temperature gaseous refrigerant flowing from the first compressor 110 has a high temperature and can release heat and liquefy, the anti-condensation pipe 160 can utilize the high temperature effect of the first refrigerant and a small portion of the heat released during liquefaction. This heats the outer perimeter of the enclosure, preventing the extremely low internal temperature (e.g., -50°C) from affecting the surrounding air when items are stored. Specifically, the surrounding air would be rapidly cooled by the extremely low internal environment when the door is opened or closed, causing condensation around the enclosure. The anti-condensation pipe 160 prevents this condensation, improving the enclosure's airtightness and cold-keeping effect.

[0075] In some embodiments, such as Figure 3 and Figure 5 As shown, the low-temperature refrigeration circuit 200 includes a pressure relief valve 261, a second throttle 220, and an evaporator 230 connected in parallel with the pressure relief valve 261. The opening degree of the pressure relief valve 261 in the open state is greater than the opening degree of the second throttle 220. The pressure relief valve 261 is configured to open for a third preset time t3 before the second compressor 210 starts, which is less than 0.5 seconds. The third preset time t3 is greater than the second preset time t2.

[0076] The pressure relief valve 261 is a valve connected in parallel in the cryogenic refrigeration circuit 200 to regulate system pressure. It can be an electromagnetic proportional valve or an electrically controlled valve. The pressure relief valve 261 has at least a closed state and an open state, and its opening degree can be adjusted. The opening degree of the pressure relief valve 261 in the open state (i.e., the maximum opening degree) is greater than the opening degree of the second throttling device 220. When the pressure relief valve 261 is fully open, the liquid refrigerant flowing from the intermediate heat exchanger 300 has a greater pressure drop than the second throttling device 220 after flowing through the pressure relief valve 261. This allows more of the second refrigerant to quickly flash vaporize after flowing through the pressure relief valve 261, thereby instantly increasing the pressure and instantaneous flow rate of the second compressor 210 on the suction side. In other words, the higher-pressure gaseous second refrigerant, when flowing towards the second compressor 210, can provide greater power to the rotating parts of the second compressor 210, thus achieving the effect of rapid start-up of the second compressor 210.

[0077] Furthermore, after the second compressor 210 is started, the large supply of the second refrigerant (gaseous) increases the instantaneous flow rate on the suction side of the second compressor 210, which reduces the system's startup pressure surge and thus improves the operational stability of the cryogenic refrigeration circuit 200. Moreover, the compression of the large amount of second refrigerant further enhances the refrigeration startup response speed of the cryogenic refrigeration circuit 200.

[0078] The second preset time t2 refers to the time interval from the opening of the pressure relief valve 261 to the start of the second compressor 210. By activating the pressure relief valve 261 in advance, the second compressor 210 can generate a large amount of flash steam on its suction side at the moment of startup, and enable the second compressor 210 to quickly drive a large amount of the second refrigerant to undergo compression and circulation.

[0079] The third preset time t3 is the continuous opening time of the pressure relief valve 261. Since the second compressor 210 needs a certain amount of time to adjust from a static state to a fully started state, the pressure relief valve 261 needs to remain open during this period to provide additional power for the start-up of the second compressor 210 through flash steam.

[0080] For example, the second preset time t2 can be 0.1-0.5s. For instance, the second preset time t2 can be 0.1s, 0.2s, 0.3s, 0.4s, or 0.5s. The larger the maximum opening degree of the pressure relief valve 261, the smaller the second preset time t2 can be, meaning the earlier start-up time of the pressure relief valve 261 can be.

[0081] Correspondingly, the third preset time t3 can be 1s-3s, meaning the third preset time t3 is greater than the second preset time t2. For example, the third preset time t3 can be 1s, 1.5s, 2s, 2.5s, or 3s. Similarly, if the maximum opening of the pressure relief valve 261 is larger, that is, the pressure value of the flash steam is higher, the corresponding third preset time t3 can be smaller, that is, the continuous start-up time of the pressure relief valve 261 can be shorter, so as to further reduce the start-up time of the second compressor 210.

[0082] Thus, by setting the pressure relief valve 261 to open in advance before the second compressor 210 starts, its large diameter characteristic accelerates the flash flow of the second refrigerant in the low-temperature refrigeration circuit 200, reduces the accumulation of liquid refrigerant in the intermediate heat exchanger 300, so that the rapidly generated flash vapor can act on the rotor side of the second compressor 210, thereby accelerating the starting power of the second compressor 210 and reducing the starting time.

[0083] Traditional solutions rely on a single throttle to regulate refrigerant flow, which can cause pressure surges due to insufficient refrigerant flow at the moment the second compressor 210 starts. This solution, by adding a pressure relief valve 261 and its timing control, proactively establishes an auxiliary flow path before the second compressor 210 starts, effectively reducing system pressure fluctuations and increasing the start-up speed of the second compressor 210. Thus, the pressure relief valve 261 solves the problem of reduced heat exchange efficiency caused by poor refrigerant flow during the second compressor 210's start-up. Simultaneously, the pressure pre-balancing mechanism suppresses sudden changes in suction flow, significantly improving system operational stability and the start-up speed of the second compressor 210.

[0084] To further balance system pressure, such as Figure 3 and Figure 5 As shown, the low-temperature refrigeration circuit 200 also includes an expansion tank 262 and an expansion valve 263. One end of the expansion valve 263 is connected to the expansion tank 262, and the other end of the expansion valve 263 is connected to the end of the pressure relief valve 261 away from the intermediate heat exchanger 300.

[0085] For example, the expansion valve 263 is configured such that the expansion valve 263 and the pressure relief valve 261 open synchronously, and the expansion valve 263 closes after a fourth preset time t4, wherein the fourth preset time t4 is greater than the third preset time t3.

[0086] The fourth preset time t4 can be between 2s and 5s. For example, the fourth preset time t4 can be 2s, 3s, 4s, or 5s, and the fourth preset time t4 is greater than the third preset time t3. For example, if the first preset time is 4 minutes, the second, third, and fourth preset times are 0.3s, 2s, and 3s, respectively.

[0087] Expansion tank 262 refers to a pressure buffer container used to store the gaseous second refrigerant in the cryogenic refrigeration circuit 200. Expansion tank 262 can be a rigid container structure to increase the effective volume in the cryogenic refrigeration circuit 200. Alternatively, expansion tank 262 can be a closed container with an elastic deformation structure, allowing for flexible adjustment and balancing of the internal capacity according to system pressure changes, absorbing volume fluctuations of the second refrigerant through elastic deformation. Expansion valve 263 refers to a controlled solenoid valve or electrically controlled valve used to control whether expansion tank 262 is connected to the cryogenic refrigeration circuit 200 for pressure balancing.

[0088] For example, before the second compressor 210 starts, the pressure relief valve 261 opens to rapidly increase the pressure of the cryogenic refrigeration circuit 200 through the flash evaporation of the second refrigerant. At the same time, the expansion valve 263 opens simultaneously, connecting the expansion tank 262, the outlet of the pressure relief valve 261, and the return port of the second compressor 210. The expansion tank 262 absorbs the flashed refrigerant in the cryogenic refrigeration circuit 200 to balance the system pressure surge when the pressure relief valve 261 starts. After the second compressor 210 finishes starting, the pressure relief valve 261 closes first, and the expansion valve 263 closes subsequently to isolate the expansion tank 262 from the cryogenic refrigeration circuit 200, and the system enters normal operation. The buffering effect of the expansion tank 262, combined with the timing control of the expansion valve 263, ensures that the cryogenic refrigeration circuit 200 maintains a suitable pressure gradient during the start-up transition phase, allowing the refrigerant flow state to quickly reach the stable operating condition requirements.

[0089] like Figure 2As shown, the main control module 610 is electrically connected to the pressure relief valve 261 and the expansion valve 263. Thus, the main control module 610 can send control signals to the pressure relief valve 261 and the expansion valve 263 respectively when needed, according to a preset program, to control the pressure relief valve 261 and the expansion valve 263 to be in an open or closed state.

[0090] For example, the main control module 610 includes time-delay relays, one of which is connected to the pressure relief valve 261, and the other is connected to the expansion valve 263. The pressure relief valve 261 and the expansion valve 263 are normally closed valves. The two time-delay relays are activated synchronously to control the simultaneous opening of the pressure relief valve 261 and the expansion valve 263. One time-delay relay controls the pressure relief valve 261 to close after a third preset time t3, and the other time-delay relay controls the expansion valve 263 to close after a fourth preset time t4 to isolate the expansion tank 262 from the cryogenic refrigeration circuit.

[0091] Alternatively, a time-delay relay can be electrically connected to the circulating pump 410 and the bypass valve 420, with the bypass valve 420 also being normally closed. When the first compressor 110 and the condenser fan 500 start, the time-delay relay controls the circulating pump 410 and the bypass valve 420 to start synchronously. Furthermore, after a first preset time t1, the time-delay relay controls the circulating pump 410 and the bypass valve 420 to close synchronously.

[0092] It should be noted that before starting the bypass circuit 400, it is also necessary to check the temperature of the intermediate heat exchanger 300 on the evaporator side. When the temperature of the intermediate heat exchanger 300 on the evaporator side is within the range of -30℃ to -20℃, control the start of the bypass circuit 400.

[0093] In some embodiments, such as Figure 3 and Figure 5 As shown, the low-temperature refrigeration circuit 200 also includes an oil separator 242, which is located between the second condenser 251 and the liquid receiver 252. The oil separator 242 is used to filter the lubricating oil mixed in the second refrigerant. The filtered and accumulated lubricating oil is then directed to the oil return port of the second compressor 210 to improve its lubrication effect.

[0094] like Figure 3 As shown, pressure sensor 620 is positioned between the second filter 241 and the receiver 252 to detect the pressure of the second refrigerant between the outlet of the second compressor 210 and the intermediate heat exchanger 300. This facilitates the calculation of the saturation temperature and subcooling of the second refrigerant.

[0095] Secondly, some embodiments of this application provide a refrigeration device that includes the cascade refrigeration system described in the first aspect. Since this refrigeration device employs all the cascade refrigeration systems described in the first aspect, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated further here.

[0096] Based on this, in the cascade refrigeration system provided in this application embodiment, a liquid receiver 252 is provided after the second condenser 251 in the low-temperature refrigeration circuit 200 to buffer the liquid phase of the second refrigerant and prevent liquid accumulation at the intermediate heat exchanger 300.

[0097] A bypass circuit 400, including a circulation pump 410 and a bypass valve 420, is installed after the liquid receiver 252. Before the second compressor 210 is started, the bypass circuit 400 forces the liquid second refrigerant to flow, causing it to flow through the intermediate heat exchanger 300 to exchange heat with the first refrigerant in the high-temperature refrigeration circuit 100. The refrigerant is then deeply cooled by the cooling energy generated by the evaporation of the first refrigerant in the intermediate heat exchanger 300. This achieves pre-circulation of the second refrigerant, thereby improving the system response speed.

[0098] Based on this, a large-diameter pressure relief valve 261 is installed at the outlet of the intermediate heat exchanger 300. At the moment the second compressor 210 starts, the liquid refrigerant accumulated in the intermediate heat exchanger 300 is rapidly flashed, generating a large amount of refrigeration vapor. This instantly increases the suction pressure and mass flow rate of the second compressor 210, helping the second compressor 210 to quickly establish a strong refrigeration cycle.

[0099] Thirdly, some embodiments of this application provide a control method for a cascade refrigeration system, used in the cascade refrigeration system of the first aspect, such as... Figure 6 As shown, the control method includes: Start the high-temperature cooling circuit.

[0100] By first starting the high-temperature refrigeration circuit to pre-cool the second refrigerant at the intermediate heat exchanger 300, the low-temperature refrigeration circuit 200 is started quickly, and the second refrigerant is rapidly circulated and cooled in the low-temperature refrigeration circuit 200, so as to provide preset conditions for the start-up of the second compressor 210 in the low-temperature refrigeration circuit 200.

[0101] Start the bypass circuit to drive the refrigerant circulation within the low-temperature refrigeration circuit.

[0102] By configuring the bypass circuit 400, the second refrigerant can circulate along the low-temperature refrigeration circuit 200 under the drive of the circulating pump 410 before the second compressor 210 is started. This circulating second refrigerant prevents it from accumulating in the intermediate heat exchanger 300, thus not affecting the circulation and heat exchange effect of the refrigerant in the low-temperature refrigeration circuit 200. Furthermore, it allows the second refrigerant to fully exchange heat and cool down with the high-temperature refrigeration circuit 100 through the intermediate heat exchanger 300, thereby ensuring that the second refrigerant has a high degree of subcooling.

[0103] If the temperature of the refrigerant flowing out of the intermediate heat exchanger in the low-temperature refrigeration circuit is lower than the saturation temperature, then the bypass circuit is closed and the low-temperature refrigeration circuit is started.

[0104] The determination of the relationship between the actual temperature and the saturation temperature of the second refrigerant allows the bypass circuit 400 to be fully activated for a first preset time t1 (e.g., 3-5 minutes) with redundancy, so that the second refrigerant at the intermediate heat exchanger 300 has a higher degree of subcooling.

[0105] Alternatively, the pressure value in the low-temperature refrigeration circuit 200 can be detected using temperature and pressure sensors. Then, the saturation temperature corresponding to the second refrigerant can be obtained based on the pressure curve. The actual temperature of the intermediate heat exchanger 300 on the condensing side can be compared with the saturation temperature to obtain the corresponding subcooling.

[0106] Since the control method of the cascade refrigeration system described above is applied to the cascade refrigeration system in the first aspect, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be repeated here.

[0107] In some embodiments, before activating the cryogenic cooling circuit, such as Figure 6 As shown, the control method for a cascade refrigeration system also includes: Open the pressure relief valve.

[0108] The low-temperature refrigeration circuit will be activated after the second preset time.

[0109] After the second refrigerant is pre-cooled by the circulating pump 410 and the bypass circuit 400, the pressure relief valve 261 can be activated to allow the liquid second refrigerant in the intermediate heat exchanger 300 to pass through the pressure relief valve 261 and flash vaporize. The vaporized second refrigerant can then fill the pipeline between the pressure relief valve 261 and the second compressor 210. At this time, the second compressor 210 is started so that the higher-pressure flash refrigerant can do work on the rotating parts of the second compressor 210, thereby increasing the start-up speed of the second compressor 210. This also allows more second refrigerant to flow into the second compressor 210 for compression, thereby increasing the cooling response speed in the low-temperature refrigeration circuit 200.

[0110] like Figure 7 As shown, the main control module 610 includes a processor 611, a communication interface 612, a memory 613, and a communication bus 614. The processor 611, communication interface 612, and memory 613 communicate with each other via the communication bus 614. The memory 613 is used to store computer programs.

[0111] In one embodiment of this application, when the processor 611 executes the computer program stored in the memory 613, it implements the steps of any of the foregoing method embodiments.

[0112] This application also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the control method for the cascade refrigeration system provided in any of the foregoing method embodiments.

[0113] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0114] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a general-purpose hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the parts that contribute to the related technology, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM (Read-Only Memory) / RAM (Random Access Memory), magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments or some parts of embodiments.

[0115] Although terms such as first, second, third, etc., may be used in this document to describe multiple elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or segment from another. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or segment discussed below may be referred to as the second element, component, region, layer, or segment without departing from the teachings of the exemplary embodiments.

[0116] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A cascade refrigeration system, characterized in that, include: Intermediate heat exchanger; A high-temperature refrigeration circuit includes a first compressor, a first condenser, a first expansion valve, and an intermediate heat exchanger connected in sequence, wherein the intermediate heat exchanger is the evaporator side in the high-temperature refrigeration circuit; The low-temperature refrigeration circuit includes a second compressor, the intermediate heat exchanger, a second throttling device, and an evaporator connected in sequence, wherein the intermediate heat exchanger is the condenser side in the low-temperature refrigeration circuit; A bypass circuit is provided within the low-temperature refrigeration circuit; the bypass circuit includes a circulation pump and is configured such that: before the second compressor starts, the high-temperature refrigeration circuit starts, and the bypass circuit is open for a first preset time to drive the refrigerant to circulate along the low-temperature refrigeration circuit.

2. The cascade refrigeration system according to claim 1, characterized in that, The bypass circuit is connected in parallel between the second compressor and the intermediate heat exchanger; or, the bypass circuit is connected in parallel between the intermediate heat exchanger and the second throttle. The bypass circuit includes a bypass valve connected in series with the circulating pump, and the bypass valve is a check valve or an electrically controlled valve; The one-way valve is configured to prevent refrigerant from flowing backward in the bypass circuit, and the circulation pump is started to open the bypass circuit; The electrically controlled valve is opened and the circulating pump is started to open the bypass circuit.

3. The cascade refrigeration system according to claim 1, characterized in that, The bypass circuit is located between the second compressor and the intermediate heat exchanger; The cryogenic refrigeration circuit includes a second filter connected upstream of the intermediate heat exchanger, and the two ends of the bypass circuit are connected in parallel with the two ends of the second filter.

4. The cascade refrigeration system according to claim 1, characterized in that, The cryogenic refrigeration circuit also includes: A second condenser is disposed between the second compressor and the intermediate heat exchanger; And a liquid receiver connected between the second condenser and the intermediate heat exchanger, wherein the bypass circuit is located downstream of the liquid receiver.

5. The cascade refrigeration system of claim 4, wherein, The cascade refrigeration system further includes a condenser fan, and the second condenser and the first condenser are disposed on the same side or opposite sides of the condenser fan.

6. The cascade refrigeration system of any of claims 1-5, wherein, The cryogenic refrigeration circuit includes: The pressure relief valve, the second throttle and the evaporator are connected in parallel with the pressure relief valve, and the opening degree of the pressure relief valve in the open state is greater than the opening degree of the second throttle; The pressure relief valve is configured to open for a third preset time before the second compressor starts, wherein the second preset time is 0.1s-0.5s and the third preset time is longer than the second preset time.

7. The cascade refrigeration system according to claim 6, characterized in that, The cryogenic refrigeration circuit also includes an expansion tank and an expansion valve. One end of the expansion valve is connected to the expansion tank, and the other end of the expansion valve is connected to the end of the pressure relief valve away from the intermediate heat exchanger.

8. The cascade refrigeration system according to claim 7, characterized in that, The expansion valve is configured to: The expansion valve and the pressure relief valve open synchronously, and the expansion valve closes after a fourth preset time, the fourth preset time being longer than the third preset time.

9. The cascade refrigeration system of any of claims 1-5, wherein, The cascade refrigeration system also includes: A pressure sensor is installed in the cryogenic refrigeration circuit to detect the pressure parameters between the second compressor and the second throttle. A first temperature sensor is installed in the intermediate heat exchanger to detect the evaporator side temperature of the intermediate heat exchanger. A second temperature sensor is installed in the intermediate heat exchanger to detect the condenser side temperature of the intermediate heat exchanger. The system also includes a main control module, which is electrically connected to the pressure sensor, the first temperature sensor, and the second temperature sensor, and is used to adjust the operating status of the low-temperature refrigeration circuit and the high-temperature refrigeration circuit.

10. A refrigeration appliance characterized in that, Includes the cascade refrigeration system as described in any one of claims 1-9.

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