Ultralow-temperature cascade unit and refrigerating system thereof

Abstract

The utility model relates to the technical field of refrigerating systems, in particular to an ultralow-temperature cascade unit and a refrigerating system thereof. The ultralow-temperature cascade unit comprises a unit condenser and a unit evaporator, the unit condenser communicates with the interior of the high-temperature heat exchange loop, the unit evaporator communicates with the interior of the low-temperature heat exchange loop, and the high-temperature heat exchange loop comprises a high-temperature compressor, a first exhaust pipe, a first air inlet pipe and a bypass pipe set. The first exhaust pipe is communicated between an air outlet of the high-temperature compressor and the unit condenser, the first air inlet pipe is communicated between the unit condenser and an air inlet of the high-temperature compressor, the first exhaust pipe and the first air inlet pipe are communicated through the bypass pipe set, and the bypass pipe set and the unit condenser are arranged in parallel. The air conditioner has the advantages that the bypass pipe set guides the high-temperature medium in the first exhaust pipe back into the high-temperature compressor, so that the high-temperature compressor is kept in a running state, and the low-temperature compressor is prevented from being started and stopped frequently.

Description

Technical Field

[0001] This utility model relates to the field of refrigeration system technology, and in particular to an ultra-low temperature cascade unit and its refrigeration system. Background Technology

[0002] In an ultra-low temperature cascade compressor unit, two heat exchange loops exchange heat within a cascade heat exchanger. These loops include a high-temperature compressor and a low-temperature compressor. Since one compressor is located in the high-temperature loop and the other in the low-temperature loop, when the terminal load changes, the low-temperature compressor starts first, followed by the high-temperature compressor. When the terminal load stabilizes, the low-temperature compressor unloads first, followed by the high-temperature compressor. Therefore, there is a time delay T1 between the start-up of the high-temperature and low-temperature compressors, the length of which depends on the pressure at the cascade heat exchanger.

[0003] However, when the cryogenic cascade unit is under low load (e.g., with a small temperature difference), the cryogenic compressor will unload and stop operating after a short period due to the low load pressure on the terminal evaporator. Similarly, the high-temperature compressor will reach its corresponding unloading condition and stop operating after a short period. In other words, both the high-temperature and cryogenic compressors will frequently start and stop under low load conditions. When pressure changes at the cascade heat exchanger cause the required start-stop interval T1 of the high-temperature compressor to lengthen, the cryogenic compressor bears the load of the entire cryogenic heat exchange circuit during the delay before the high-temperature compressor starts. Its load is high, and when the aforementioned delay time T1 exceeds the high-pressure operating limit T2 set by the cryogenic compressor, an alarm will be triggered, and the compressor will unload and stop operating. The high-temperature compressor can only start normally after several starts and high-pressure unloadings of the cryogenic compressor, thus significantly affecting the stability and durability of the cryogenic compressor. Utility Model Content

[0004] To address the aforementioned technical problems, this utility model provides an ultra-low temperature cascade unit.

[0005] An ultra-low temperature cascade unit includes: a high-temperature heat exchange circuit, a low-temperature heat exchange circuit, and a cascade heat exchanger. The cascade heat exchanger has independent high-temperature heat exchange channels and low-temperature heat exchange channels, which can exchange heat with each other. The high-temperature heat exchange channels are located in the high-temperature heat exchange circuit, and the low-temperature heat exchange channels are located in the low-temperature heat exchange circuit. The unit also includes a condenser and an evaporator. The condenser is connected to the high-temperature heat exchange circuit, and the evaporator is connected to the low-temperature heat exchange circuit. The high-temperature heat exchange circuit includes a high-temperature compressor, a first exhaust pipe, a first inlet pipe, and a bypass pipe assembly. The first exhaust pipe is connected between the outlet of the high-temperature compressor and the condenser. The first inlet pipe is connected between the condenser and the inlet of the high-temperature compressor. The first exhaust pipe and the first inlet pipe are connected through the bypass pipe assembly, which is arranged in parallel with the condenser.

[0006] With this setup, since the high-temperature heat exchange channel and the low-temperature heat exchange channel are independent and not connected, only heat exchange will occur between them, without any refrigerant mixing. The high-temperature heat exchange channel is located in the high-temperature heat exchange loop. For the high-temperature heat exchange loop, the high-temperature heat exchange channel acts as an evaporator (here, an evaporator refers to a device in a typical refrigeration system that cools by absorbing heat through refrigerant evaporation, not the unit evaporator in this embodiment; the condenser mentioned below also does not refer to the unit condenser). Liquid refrigerant absorbs heat and cools within it, thereby cooling the low-temperature heat exchange channel. For the low-temperature heat exchange loop, the low-temperature heat exchange channel acts as a condenser. The refrigerant flows through the low-temperature heat exchange loop and exchanges heat with the high-temperature heat exchange channel, thus cooling down. After being cooled in the low-temperature heat exchange channel, the refrigerant can provide more cooling capacity to the unit evaporator at a lower temperature, achieving an ultra-low temperature cooling effect. Furthermore, the first exhaust pipe is connected between the outlet of the high-temperature compressor and the unit condenser, the first intake pipe is connected between the unit condenser and the intake of the high-temperature compressor, and the first exhaust pipe and the first intake pipe are connected through a bypass pipe group, which is set in parallel with the unit condenser. The advantage of this setup is that the medium flowing out of the high-temperature compressor's outlet is high-temperature and high-pressure, while the first exhaust pipe connects the high-temperature compressor's outlet and the unit's condenser. Therefore, the high-temperature and high-pressure medium flows from the high-temperature compressor to the unit's condenser through the first exhaust pipe, while the medium flowing back from the unit's condenser to the high-temperature compressor's inlet is low-temperature and low-pressure. When the medium pressure is too low, it can easily cause the high-temperature compressor to unload. Therefore, through a bypass pipe group connected to both the first exhaust pipe and the first inlet pipe, a portion of the high-temperature and high-pressure medium in the first exhaust pipe is diverted to the first inlet pipe. In other words, the pressure of the medium in the first inlet pipe increases. The higher pressure allows the high-temperature compressor to remain running, so the low-temperature compressor no longer needs to bear the load in the low-temperature heat exchange circuit alone due to the high-temperature compressor unloading. Thus, the low-temperature compressor will no longer unload due to excessive load, thereby solving the problem of frequent start-stop of the low-temperature compressor.

[0007] In one embodiment, the bypass pipe assembly includes an exhaust bypass pipe and an intake bypass pipe. One end of the exhaust bypass pipe is connected to the first exhaust pipe, and the other end is connected to the intake bypass pipe. The intake bypass pipe is connected to the first intake pipe, and a first switch is provided on the exhaust bypass pipe.

[0008] In one embodiment, the high-temperature heat exchange circuit further includes a first liquid reservoir and a first liquid supply pipe. The unit condenser is connected to the first liquid reservoir, and the first liquid reservoir is connected to the high-temperature heat exchange channel through the first liquid supply pipe. The bypass pipe group further includes a first liquid reservoir bypass pipe, one end of which is connected to the first liquid supply pipe, and the other end is connected to the suction bypass pipe. The first liquid reservoir bypass pipe and the exhaust bypass pipe converge and mix in the suction bypass pipe.

[0009] In one embodiment, the first reservoir bypass pipe is provided with a first throttling element and a first temperature sensing control element, the first throttling element being configured to change its opening degree in response to the control of the first temperature sensing control element.

[0010] In one embodiment, the high-temperature heat exchange circuit includes a first oil separator and a first oil separator exhaust pipe connected to the first oil separator, the first exhaust pipe being connected to the unit condenser through the first oil separator and the first oil separator exhaust pipe.

[0011] The high-temperature heat exchange circuit further includes a first balance tube, one end of which is connected to the first liquid reservoir and the other end of which is connected to the exhaust pipe of the first oil separator.

[0012] In one embodiment, the cryogenic heat exchange circuit includes a cryogenic compressor, a second oil separator, a second oil separator exhaust pipe, a second liquid reservoir, and a second liquid reservoir drain pipe. The cryogenic compressor is connected to the second oil separator, the second oil separator is connected to the cryogenic heat exchange channel through the second oil separator exhaust pipe, the cryogenic heat exchange channel is connected to the second liquid reservoir drain pipe, and the second liquid reservoir drain pipe is connected to the second liquid reservoir.

[0013] In one embodiment, the low-temperature heat exchange circuit further includes a second liquid reservoir bypass pipe, one end of which is connected to the second liquid reservoir drain pipe and the other end of which is connected to the second oil separator exhaust pipe.

[0014] In one embodiment, a second switch is provided on the bypass pipe of the second reservoir, and a second temperature sensor is provided on the exhaust pipe of the second oil separator. The second temperature sensor is capable of detecting the temperature in the exhaust pipe of the second oil separator, and the second switch is configured to open or close in response to the triggering of the second temperature sensor.

[0015] In one embodiment, the cryogenic cascade unit further includes a sustaining unit and a sustaining heat exchanger. The sustaining heat exchanger is provided with a third heat exchange channel and a fourth heat exchange channel. The third heat exchange channel and the fourth heat exchange channel are independent of each other and can exchange heat with each other. The sustaining unit is connected to the third heat exchange channel. The cryogenic heat exchange circuit includes a cryogenic compressor and a second liquid receiver. The cryogenic compressor is connected to the second liquid receiver, and the second liquid receiver is connected to the fourth heat exchange channel.

[0016] This utility model also provides a refrigeration system, including the ultra-low temperature cascade unit as described above.

[0017] Compared to existing technologies, this invention utilizes the heat exchange between the high-temperature and low-temperature heat exchange channels in a high-temperature heat exchanger. The high-temperature heat exchange channel acts as an evaporator in the high-temperature heat exchange circuit, thereby cooling the low-temperature heat exchange channel. The low-temperature heat exchange channel also functions as a condenser, further reducing the amount of refrigerant flowing through it in the low-temperature heat exchange circuit, thus achieving further cooling. Furthermore, by setting up a bypass pipe assembly, the first exhaust pipe and the first intake pipe, which are connected to the compressor's inlet and outlet, are connected through the bypass pipe assembly. This allows a portion of the high-temperature, high-pressure medium in the first exhaust pipe to be diverted to the first intake pipe. The higher pressure ensures that the high-temperature compressor remains continuously running. Therefore, the low-temperature compressor no longer needs to bear the load of the low-temperature heat exchange circuit due to the unloading of the high-temperature compressor, thus solving the problem of frequent start-stop of the low-temperature compressor. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of one embodiment of the cryogenic cascade unit provided by this utility model.

[0019] The symbols in the diagram represent the following meanings:

[0020] 100. Ultra-low temperature cascade unit; 10. High temperature heat exchange circuit; 11. High temperature compressor; 111. First exhaust pipe; 112. First intake pipe; 12. Bypass pipe assembly; 121. Exhaust bypass pipe; 1211. First switch; 1212. First exhaust solenoid valve; 1213. First exhaust temperature sensor; 122. Suction bypass pipe; 123. First liquid reservoir bypass pipe; 1231. First throttling device; 1232. Fourth switch; 13. First liquid reservoir; 131. First supply pipe; 1311. First supply solenoid valve; 1312. First electronic expansion valve; 132. First liquid reservoir drain pipe; 14. First oil separator; 141. First oil return pipe; 142. First oil separator exhaust pipe; 15. First balance pipe; 16. First gas-liquid separator; 161. First gas separator inlet pipe; 20. Low-temperature heat exchange circuit; 21. Low-temperature compressor; 22. Second oil separator; 221. Second oil separator exhaust pipe; 2211. Second temperature sensing element; 23. Second liquid receiver; 231. Second liquid receiver drain pipe; 232. Second liquid receiver bypass pipe; 2321. Second switch; 233. Second liquid receiver inlet pipe; 234. Second liquid receiver condenser pipe; 235. Second liquid receiver outlet pipe; 24. Second exhaust pipe; 25. Second gas-liquid separator; 251. Second gas-liquid separator inlet pipe; 252. Second gas-liquid separator outlet pipe; 26. Second oil return pipe; 30. Maintaining unit; 31. Maintaining heat exchanger; 32. Third switch; 40. Cascade heat exchanger. Detailed Implementation

[0021] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0022] It should be noted that when a mechanism is referred to as being "fixed to" or "set on" another mechanism, it can be directly on the other mechanism or there may be an intervening mechanism. When a mechanism is considered to be "connected to" another mechanism, it can be directly connected to the other mechanism or there may be an intervening mechanism. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application's specification are for illustrative purposes only and do not represent the only possible implementation.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0024] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature and the second feature are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0025] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0026] This utility model provides an ultra-low temperature cascade unit 100, which can allow the medium in the first exhaust pipe 111 with higher temperature and pressure to return to the first intake pipe 112 through the bypass pipe group 12, thereby keeping the high temperature compressor 11 under a preset load. This ensures that the high temperature compressor 11 is always in operation, avoiding the need for the low temperature compressor 21 to bear the load in the low temperature heat exchange circuit 20 alone, and preventing it from frequently starting and stopping after overload.

[0027] Please see Figure 1The ultra-low temperature cascade unit 100 includes a high-temperature heat exchange circuit 10, a low-temperature heat exchange circuit 20, and a cascade heat exchanger 40. The cascade heat exchanger 40 has independent high-temperature and low-temperature heat exchange channels that can exchange heat with each other. The high-temperature heat exchange channel is located in the high-temperature heat exchange circuit 10, and the low-temperature heat exchange channel is located in the low-temperature heat exchange circuit 20. The ultra-low temperature cascade unit 100 also includes a condenser and an evaporator. The condenser is connected to the high-temperature heat exchange circuit 10, and the evaporator is connected to the low-temperature heat exchange circuit 20. Thus, because the high-temperature and low-temperature heat exchange channels are independent and not connected, only heat exchange occurs between them, and there is no refrigerant mixing problem. The high-temperature heat exchange channel is located in the high-temperature heat exchange circuit 10. For the high-temperature heat exchange circuit 10, the high-temperature heat exchange channel acts as an evaporator (here, an evaporator refers to a device in a typical refrigeration system that cools by absorbing heat through refrigerant evaporation, not the unit evaporator in this embodiment; the condenser mentioned below also does not refer to the unit condenser). Liquid refrigerant absorbs heat and cools within it, thereby cooling the low-temperature heat exchange channel. For the low-temperature heat exchange circuit 20, the low-temperature heat exchange channel acts as a condenser. The refrigerant flows through the low-temperature heat exchange circuit 20 and exchanges heat with the high-temperature heat exchange channel, thus cooling down. After being cooled in the low-temperature heat exchange channel, the refrigerant can provide more cooling capacity to the unit evaporator at a lower temperature, thereby achieving an ultra-low temperature cooling effect.

[0028] The high-temperature heat exchange circuit 10 includes a high-temperature compressor 11, and the low-temperature heat exchange circuit 20 includes a low-temperature compressor 21. When the load at the evaporator changes, the low-temperature compressor 21 starts first, followed by the high-temperature compressor 11. When the load at the evaporator stabilizes, the low-temperature compressor 21 unloads first, followed by the high-temperature compressor 11. Therefore, there is a time delay T1 between the start-up of the high-temperature compressor 11 and the low-temperature compressor 21, the length of which depends on the pressure at the cascade heat exchanger 40. When the cryogenic cascade unit 100 is under low-load conditions (e.g., small temperature difference), the low-temperature compressor 21 will unload and stop operating after a short period of operation due to the low load pressure on the evaporator. Similarly, the high-temperature compressor 11 will reach the corresponding unloading condition and stop operating after a short period of operation. In other words, under low-load conditions, both the high-temperature compressor 11 and the low-temperature compressor 21 will frequently start and stop. When the pressure change at the cascade heat exchanger 40 causes the required start-stop interval T1 of the high-temperature compressor 11 to lengthen, during the period when the high-temperature compressor 11 is delayed in starting, the low-temperature compressor 21 bears the load of the entire low-temperature heat exchange circuit 20, and its load is relatively high. When the aforementioned delay time T1 exceeds the high-pressure operating limit time T2 set by the low-temperature compressor 21, it will trigger an alarm and unload and stop operation. After the low-temperature compressor 21 has started and unloaded under high pressure several times, the high-temperature compressor 11 can start normally. Therefore, the stability and durability of the low-temperature compressor 21 are significantly affected.

[0029] It needs to be explained that the cryogenic cascade compressor unit 100 is only in normal operation when both the cryogenic compressor 21 and the high-temperature compressor 11 are operating normally. The start-up correlation between the high-temperature compressor 11 and the cryogenic compressor 21 is triggered by multiple negative pressure monitoring points. Therefore, when the evaporator of the above-mentioned unit has a small negative pressure, the change in negative pressure in its entire flow path is correspondingly slower. This results in a time delay between the start-up of the high-temperature compressor 11 and the cryogenic compressor 21, rather than simultaneous start-up or shutdown, causing the aforementioned technical problem. The high-temperature compressor 11 and the cryogenic compressor 21 belong to the high-temperature cycle and the low-temperature cycle, respectively. The high-temperature cycle may use a medium-temperature refrigerant, such as R404A or R507, while the low-temperature cycle may use a low-temperature refrigerant, such as R23 or R508B. These two cycles are connected by an intermediate heat exchanger, namely the aforementioned cascade heat exchanger 40. If the high-temperature cycle fails to dissipate heat sufficiently, the condensing temperature of the low-temperature cycle will rise, leading to an increase in the compression ratio, a decrease in efficiency, and even failure to reach the target low temperature. The heat load of the low-temperature cycle needs to match the cooling capacity of the high-temperature cycle; otherwise, it will cause the intermediate heat exchanger to be overloaded or underloaded, affecting the system stability. Therefore, when the high-temperature compressor 11 has not been started for a long time, the low-temperature compressor 21 will be unloaded due to excessive load.

[0030] In response to this, the ultra-low temperature cascade unit 100 provided by this utility model includes a high temperature heat exchange circuit 10 comprising a high temperature compressor 11, a first exhaust pipe 111, a first intake pipe 112, and a bypass pipe assembly 12. The first exhaust pipe 111 is connected between the outlet of the high temperature compressor 11 and the unit condenser. The first intake pipe 112 is connected between the unit condenser and the inlet of the high temperature compressor 11. The first exhaust pipe 111 and the first intake pipe 112 are connected through the bypass pipe assembly 12, which is arranged in parallel with the unit condenser. The advantage of this configuration is that the medium flowing out of the outlet of the high-temperature compressor 11 is high-temperature and high-pressure, while the first exhaust pipe 111 is connected between the outlet of the high-temperature compressor 11 and the unit condenser. Therefore, the high-temperature and high-pressure medium flows from the high-temperature compressor 11 to the unit condenser through the first exhaust pipe 111, while the medium flowing back from the unit condenser to the inlet of the high-temperature compressor 11 is low-temperature and low-pressure. When the pressure of the medium is too low, it is easy to cause the high-temperature compressor 11 to unload. Therefore, through the bypass pipe group 12, which is connected to both the first exhaust pipe 111 and the first inlet pipe 112, a portion of the high-temperature and high-pressure medium in the first exhaust pipe 111 is diverted to the first inlet pipe 112. In other words, the pressure of the medium in the first inlet pipe 112 increases. The higher pressure allows the high-temperature compressor 11 to always be in operation. Therefore, the low-temperature compressor 21 will no longer need to bear the load in the low-temperature heat exchange circuit 20 alone due to the unloading of the high-temperature compressor 11. Thus, the low-temperature compressor 21 will no longer unload due to excessive load, thereby solving the problem of frequent start-stop of the low-temperature compressor 21.

[0031] It should be explained that, as stated above, the connection between the first exhaust pipe 111 and the high-temperature compressor 11's outlet and the unit condenser is only limited to one end of the first exhaust pipe 111 being connected to the flow path between the unit condenser and the high-temperature compressor 11; it does not restrict the installation of other components in this flow path. In this embodiment, a first oil separator 14 is also provided between the unit condenser and the high-temperature compressor 11, and one end of the first exhaust pipe 111 is actually connected between the high-temperature compressor 11 and the first oil separator 14.

[0032] A first oil return pipe 141 is also provided between the first oil separator 14 and the high-temperature compressor 11. The lubricating oil separated in the first oil separator 14 returns to the high-temperature compressor 11 through the first oil return pipe 141.

[0033] Specifically, the bypass pipe assembly 12 includes an exhaust bypass pipe 121 and an intake bypass pipe 122. One end of the exhaust bypass pipe 121 is connected to the first exhaust pipe 111, and the other end is connected to the intake bypass pipe 122. The intake bypass pipe 122 is connected to the first intake pipe 112. A first switch element 1211 is provided on the exhaust bypass pipe 121. In this way, the high-temperature and high-pressure medium flowing out of the high-temperature compressor 11 will flow into the intake bypass pipe 122 through the exhaust bypass pipe 121, and then flow into the first intake pipe 112 through the intake bypass pipe 122. The first switch element 1211 can control the opening and closing of the exhaust bypass pipe 121.

[0034] In this embodiment, the first switching element 1211 is configured as a hot gas bypass valve. To match the use of the first switching element 1211, a first exhaust solenoid valve 1212 is also provided on the exhaust bypass pipe 121. The first switching element 1211 can control the opening and closing of the first exhaust solenoid valve 1212 according to the opening pressure. This control method will be described in detail below and will not be repeated here.

[0035] A first exhaust temperature sensor 1213 is also provided on the first exhaust pipe 111, which can detect the temperature in the first exhaust pipe 111.

[0036] Furthermore, if the hot gas bypass valve is used for bypass intake, the high return temperature will cause the high-temperature compressor 11 to exhaust temperature to be too high, resulting in problems such as lubricating oil carbonization and reduced lifespan.

[0037] To address this, the high-temperature heat exchange circuit 10 also includes a first liquid receiver 13 and a first liquid supply pipe 131. The outlet of the unit condenser is connected to the first liquid receiver 13, and the first liquid receiver 13 is connected to the high-temperature heat exchange channel through the first liquid supply pipe 131. The bypass pipe group 12 also includes a first liquid receiver bypass pipe 123. One end of the first liquid receiver bypass pipe 123 is connected to the first liquid supply pipe 131, and the other end is connected to the suction bypass pipe 122. The first liquid receiver bypass pipe 123 and the exhaust bypass pipe 121 converge and mix in the suction bypass pipe 122. Thus, since the first liquid receiver 13 is connected to the outlet of the unit condenser, the temperature and pressure of the medium inside the first liquid receiver 13 are relatively low. The medium in the first liquid receiver 13 flows into the suction bypass pipe 122 through the first liquid receiver bypass pipe 123, thereby reducing the temperature of the medium in the suction bypass pipe 122 and preventing excessive temperature.

[0038] In this embodiment, the medium flowing out of the high-temperature heat exchange channel will flow back to the high-temperature compressor 11 through the first intake pipe 112. Since the suction bypass pipe 122 is connected to the first intake pipe 112, the medium flowing out of the first liquid reservoir 13 can also reduce the temperature of the medium in the first intake pipe 112.

[0039] Furthermore, the first reservoir bypass pipe 123 is provided with a first throttling element 1231 and a first temperature sensing control element. The first throttling element 1231 is configured to change its opening degree in response to the control of the first temperature sensing control element. Thus, since the first throttling element 1231 can throttle the medium, for example by opening multiple throttling orifices and cooling the medium by liquid spraying, the first throttling element 1231 can control the temperature of the medium while throttling it. Therefore, in response to the control of the first temperature sensing control element, it limits the temperature of the medium to a preset value.

[0040] A first liquid receiver drain pipe 132 is connected between the condenser outlet of the unit and the first liquid receiver 13. The medium flowing out of the condenser of the unit flows into the first liquid receiver 13 through the first liquid receiver drain pipe 132.

[0041] The high-temperature heat exchange circuit 10 also includes a first oil separator 14 and a first oil separator exhaust pipe 142 connected to the first oil separator 14. The first exhaust pipe 111 is connected to the unit condenser through the first oil separator 14 and the first oil separator exhaust pipe 142. The high-temperature heat exchange circuit 10 also includes a first balancing pipe 15, one end of which is connected to the first liquid reservoir 13, and the other end is connected to the first oil separator exhaust pipe 142. This balances the pressure within the first liquid reservoir 13. Since the continuous flow of the medium into the first liquid reservoir 13 causes a pressure increase, the first balancing pipe 15 clears the flow to the first oil separator exhaust pipe 142, preventing the medium from being unable to continue flowing into the first liquid reservoir 13.

[0042] The high-temperature heat exchange circuit 10 also includes a first gas-liquid separator 16, which is connected to the high-temperature compressor 11 and forms a circuit. Low-temperature, low-pressure gas-liquid two-phase mixed refrigerant evaporates in the cascade heat exchanger 40. The evaporated refrigerant vapor is separated into gas and liquid phases by the first gas-liquid separator 16 and then enters the high-temperature compressor 11. The first gas-liquid separator 16 is connected to a first inlet pipe 112. A first gas separator inlet pipe 161 is also connected to the first gas separator 16, through which the medium flowing out of the high-temperature heat exchange channel in the cascade heat exchanger 40 flows into the first gas-liquid separator 16.

[0043] The cryogenic heat exchange circuit 20 includes a cryogenic compressor 21, a second oil separator 22, a second oil separator exhaust pipe 221, a second liquid reservoir 23, and a second liquid reservoir drain pipe 231. The cryogenic compressor 21 is connected to the second oil separator 22. The second oil separator 22 is connected to the cryogenic heat exchange channel through the second oil separator exhaust pipe 221. The cryogenic heat exchange channel is connected to the second liquid reservoir drain pipe 231. The second liquid reservoir drain pipe 231 is connected to the second liquid reservoir 23. Thus, the medium flowing out of the cryogenic compressor 21 first flows into the second oil separator 22, then flows through the second oil separator 22 to the cryogenic heat exchange channel, where it exchanges heat with the medium in the high-temperature heat exchange channel, and then flows to the second liquid reservoir drain pipe 231 and into the second liquid reservoir 23 for storage.

[0044] Because the inlet of the cascade heat exchanger 40 is connected to the exhaust pipe 221 of the second oil separator, the temperature at the inlet is relatively high. After heat exchange through the low-temperature heat exchange channel and the high-temperature heat exchange channel, the temperature at the outlet of the cascade heat exchanger is relatively low. In other words, the temperature difference between the inlet and outlet of the cascade heat exchanger is very large, which can easily cause damage to the structure of the cascade heat exchanger.

[0045] To address this, the low-temperature heat exchange circuit 20 also includes a second liquid reservoir bypass pipe 232. One end of the second liquid reservoir bypass pipe 232 is connected to the second liquid reservoir drain pipe 231, and the other end is connected to the second oil separator exhaust pipe 221. Since the second liquid reservoir drain pipe 231 is connected to the outlet of the low-temperature heat exchange channel, the temperature inside the second liquid reservoir drain pipe 231 is low. Therefore, the low-temperature medium inside the second liquid reservoir drain pipe 231 flows into the second liquid reservoir bypass pipe 232 and then into the second oil separator exhaust pipe 221, before re-entering the low-temperature heat exchange channel in the cascade heat exchanger. This reduces the temperature in the second oil separator exhaust pipe 221, thereby reducing the temperature difference between the inlet and outlet of the cascade heat exchanger.

[0046] Based on this scheme, a second switch 2321 is installed on the bypass pipe 232 of the second liquid receiver, and a second temperature sensor 2211 is installed on the exhaust pipe 221 of the second oil separator. The second temperature sensor 2211 can detect the temperature in the exhaust pipe 221 of the second oil separator, and the second switch 2321 is configured to open or close in response to the triggering of the second temperature sensor 2211. Thus, the second temperature sensor 2211 can detect whether the temperature inside the exhaust pipe 221 of the second oil separator is too high. When the temperature is too high, it means that the inlet and outlet temperatures of the cascade heat exchanger are relatively high. At this time, the second temperature sensor 2211 controls the second switch 2321 to open, allowing the low-temperature medium in the bypass pipe 232 of the second liquid receiver to flow back into the exhaust pipe 221 of the second oil separator, thereby reducing the temperature inside the exhaust pipe 221 of the second oil separator.

[0047] The second liquid receiver 23 is also connected to a second liquid receiver outlet pipe 235, which is connected to the inlet of the unit evaporator, so that the medium can enter the unit evaporator.

[0048] The low-temperature heat exchange circuit 20 also includes a second gas-liquid separator 25, a second gas-liquid separator inlet pipe 251, and a second gas-liquid separator outlet pipe 252. The medium flowing out from the unit evaporator enters the second gas-liquid separator 25 through the second gas-liquid separator inlet pipe 251, and after gas-liquid separation, it flows out from the second gas-liquid separator outlet pipe 252.

[0049] A second oil return pipe 26 is also connected between the cryogenic compressor 21 and the second oil separator 22. The lubricating oil separated by the second oil separator 22 flows back to the cryogenic compressor 21 through the second oil return pipe 26.

[0050] The cryogenic cascade unit 100 also includes a sustaining unit 30 and a sustaining heat exchanger 31. The sustaining heat exchanger 31 has a third heat exchange channel and a fourth heat exchange channel. The third and fourth heat exchange channels are independent of each other but can exchange heat with each other. The sustaining unit 30 is connected to the third heat exchange channel. The cryogenic heat exchange circuit 20 includes a cryogenic compressor 21 and a second liquid receiver 23. The cryogenic compressor 21 is connected to the second liquid receiver 23, and the second liquid receiver 23 is connected to the fourth heat exchange channel. Thus, the sustaining unit 30 and the sustaining heat exchanger 31 can function similarly to those in the aforementioned cascade heat exchanger 40. The third heat exchange channel in the sustaining heat exchanger 31 acts as the evaporator of the sustaining unit 30, absorbing heat in the third heat exchange channel. The medium in the fourth heat exchange channel exchanges heat with the third heat exchange channel and is further cooled, thereby further cooling the medium in the second liquid receiver 23. The second liquid reservoir 23 is connected to the second liquid reservoir condenser pipe 234 and the second liquid reservoir inlet pipe 233. The medium in the second liquid reservoir 23 enters the fourth heat exchange channel through the second liquid reservoir inlet pipe 233. The fourth heat exchange channel is equivalent to the condenser of the second liquid reservoir 23. The medium releases heat in it and is further cooled down, and then returns to the second liquid reservoir 23 through the second liquid reservoir condenser pipe 234.

[0051] A third switch 32 is provided between the maintenance unit 30 and the third heat exchange channel. The third switch 32 can be opened or closed to control whether the maintenance unit 30 participates in the cooling of the second liquid receiver 23. Its control logic is described in detail below.

[0052] This utility model also provides a control method for realizing the operation control of the ultra-low temperature cascade unit 100 as described above. The control method includes: obtaining the suction pressure PH1 of the high temperature compressor 11, comparing the suction pressure PH1 with the preset pressure, and starting the high temperature compressor 11 when PH1 ≥ preset pressure + load pressure difference and the duration reaches t1.

[0053] When PH1 < preset pressure + applied pressure difference and the duration reaches t2, the high-temperature compressor 11 is shut down;

[0054] The suction pressure PL1 of the cryogenic compressor 21 is obtained, and the suction pressure PL1 is compared with the preset pressure. When PL1 ≥ preset pressure + load pressure difference and the duration reaches t3, the cryogenic compressor 21 is started.

[0055] When PL1 < preset pressure + applied pressure difference and the duration reaches t4, the cryogenic compressor 21 is shut down. The automatic start-up and shutdown of the high-temperature compressor 11 and the cryogenic compressor 21 are achieved by acquiring the suction pressure of the high-temperature compressor 11 and the cryogenic compressor 21. The duration setting ensures that the high-temperature compressor 11 and the cryogenic compressor 21 have stabilized in this state.

[0056] In order to ensure the smooth operation of the high-temperature compressor 11 and the low-temperature compressor 21, both the high-temperature compressor 11 and the low-temperature compressor 21 include an oil pressure differential switch.

[0057] The oil pressure difference A1 in the high-temperature compressor 11 is obtained through the oil pressure differential switch, and compared with a preset oil pressure difference A2. When A1 is less than A2, a trigger time is calculated. If A1 is still less than A2 after a delay of t5, an alarm is triggered. The oil pressure difference A3 in the low-temperature compressor 21 is obtained through the oil pressure differential switch, and compared with a preset oil pressure difference A4. When A3 is less than A4, a trigger time is calculated. If A3 is still less than A4 after a delay of t6, an alarm is triggered. Since the oil pressure difference A1 is less than the preset oil pressure difference A2, and the oil pressure difference A3 is less than the preset oil pressure difference A4, it indicates that the oil pressure has dropped to a level insufficient for the safe operation of the high-temperature compressor 11 and the low-temperature compressor 21. Therefore, if the oil pressure difference does not recover to above the set level within the set delay period, the oil pressure differential switch can cut off the circuit, causing the high-temperature compressor 11 and the low-temperature compressor 21 to stop alarming, thus protecting them from damage. In this embodiment, t5 and t6 are set to 90±5s. The oil pressure differential switch needs to be equipped with a manual reset function, that is, a reset function for oil shortage faults, and a reset function 5 seconds after the switch is powered off.

[0058] The control method also includes controlling the third switch 32 mentioned above. By acquiring the internal pressure of the second reservoir 23, the third switch 32 is opened or closed according to the internal pressure of the second reservoir 23. When the internal pressure of the second reservoir 23 is too high, the third switch 32 is opened, thereby further reducing the temperature of the medium inside the second reservoir 23 and reducing the internal pressure of the second reservoir 23; conversely, the third switch 32 is closed when the internal pressure is too low.

[0059] Specifically, in this embodiment, the third switch 32 is configured as a solenoid valve.

[0060] In the low-temperature heat exchange circuit 20, the low-temperature heat exchange circuit 20 includes a low-temperature compressor 21, a second exhaust pipe 24, a first liquid reservoir 13, a first electronic expansion valve 1312, and a first liquid supply solenoid valve 1311. The second exhaust pipe 24 is connected to the low-temperature compressor 21. The control method includes: acquiring the exhaust pressure PL2 in the second exhaust pipe 24, the pressure difference ΔP1 of the first liquid supply solenoid valve 1311, and the operating status of the low-temperature compressor 21, and comparing the exhaust pressure PL2 with the preset pressure PL3 of the first liquid supply solenoid valve 1311; when PL2 > PL3, the first electronic expansion valve 1312 and the first liquid supply solenoid valve 1311 are opened, and the cascade heat exchanger 40 participates in operation; when PL2 < PL3 - ΔP1, the first electronic expansion valve 1312 and the first liquid supply solenoid valve 1311 are closed. The connection between the first liquid reservoir 13 and the high-temperature heat exchange channel is disconnected.

[0061] As described above, the bypass assembly 12 is equipped with a first switch 1211 and a first exhaust solenoid valve 1212 for controlling the opening and closing of the bypass assembly 12. The first switch 1211 is configured as a bypass valve. The control method includes: acquiring the operating status of the high-temperature compressor 11 and the low-temperature compressor 21; acquiring the suction pressure PH1 of the high-temperature compressor 11; when both the high-temperature compressor 11 and the low-temperature compressor 21 are in an unloading state, the first exhaust solenoid valve 1212 is closed; when the high-temperature compressor 11 is in an unloading state and the low-temperature compressor 21 is ready to start, the first exhaust solenoid valve 1212 is opened, and when PH1 ≥ a preset pressure, the first exhaust solenoid valve 1212 is closed; when both the high-temperature compressor 11 and the low-temperature compressor 21 are in a loading state, and the bypass valve opening pressure ≤ a set value, the first exhaust solenoid valve 1212 is opened; when both the high-temperature compressor 11 and the low-temperature compressor 21 are in a loading state, and the bypass valve opening pressure > a set value, the first exhaust solenoid valve 1212 is closed.

[0062] A fourth switch 1232 is provided in the bypass pipe 123 of the first liquid reservoir. The control method further includes: acquiring the exhaust temperature of the high-temperature compressor 11 and the on / off state of the first exhaust solenoid valve 1212; when the high-temperature compressor 11 is loaded, the first exhaust solenoid valve 1212 is open, and the exhaust temperature of the high-temperature compressor 11 is greater than a preset value, the fourth switch 1232 is open; when the high-temperature compressor 11 is loaded, the first exhaust solenoid valve 1212 is open, and the exhaust temperature of the high-temperature compressor 11 is less than the preset value, the fourth switch 1232 is closed; when the high-temperature compressor 11 is unloaded and / or the first exhaust solenoid valve 1212 is closed, the fourth switch 1232 is closed. Thus, when the fourth switch 1232 is open, the medium in the first liquid reservoir 13 will enter the suction bypass pipe 122 and reduce the temperature of the medium in the suction bypass pipe 122; conversely, when the fourth switch 1232 is closed, the first liquid reservoir 13 and the suction bypass pipe 122 are isolated.

[0063] In this embodiment, the fourth switching element 1232 is also configured as a solenoid valve.

[0064] In addition, the unit condenser includes multiple cooling components with different operating times. The control method includes: acquiring the discharge pressure PH2 of the high-temperature compressor 11; acquiring the time for the discharge pressure PH2 of the high-temperature compressor 11 to exceed the preset pressure PH3; starting at least one cooling component when PH2 > PH3; and determining the starting time of cooling components with different operating times based on the length of time PH2 > PH3. In this embodiment, the cooling component is set as a condensing fan. When the condensing fan is started, it can improve the condensing efficiency of the unit condenser. In this embodiment, when PH2 > PH3, a condensing fan with the shortest operating time that meets the condition is randomly started. When a condensing fan is running and the discharge pressure PH2 > PH3 for a certain period reaches the condensing fan start time t7, a condensing fan that meets the condition is randomly started. The condensing fan start delay time t7 shortens as the discharge pressure increases, with a minimum of 5 seconds, to adapt to the rapid start-up response at high temperatures. When the discharge pressure PH2 < PH3 and the condensing fan stops for a certain delay time t8, the fan with the longest operating time is stopped, and so on. High-temperature compressor 11 stops, and after a 5-second delay, all condenser fans stop.

[0065] Compared to existing technologies, this invention utilizes the heat exchange between the high-temperature and low-temperature heat exchange channels in the high-temperature heat exchanger. The high-temperature heat exchange channel acts as the evaporator of the high-temperature heat exchange circuit 10, thereby cooling the low-temperature heat exchange channel. The low-temperature heat exchange channel also functions as a condenser, further reducing the amount of refrigerant flowing through the low-temperature heat exchange channel in the low-temperature heat exchange circuit 20, thus achieving further cooling. Furthermore, by setting a bypass pipe assembly 12, the first exhaust pipe 111 and the first intake pipe 112, which are connected to the compressor's inlet and outlet, are connected through the bypass pipe assembly 12. This allows a portion of the high-temperature, high-pressure medium in the first exhaust pipe 111 to be diverted to the first intake pipe 112. The higher pressure ensures that the high-temperature compressor 11 remains constantly running. Therefore, the low-temperature compressor 21 no longer needs to bear the load of the low-temperature heat exchange circuit 20 due to the unloading of the high-temperature compressor 11, thus solving the problem of frequent start-stop of the low-temperature compressor 21.

[0066] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0067] The embodiments described above are merely illustrative of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A cryogenic cascade unit, characterized in that, include: The system includes a high-temperature heat exchange circuit (10), a low-temperature heat exchange circuit (20), and a cascade heat exchanger (40). The cascade heat exchanger (40) has independent high-temperature heat exchange channels and low-temperature heat exchange channels. The high-temperature heat exchange channels and the low-temperature heat exchange channels can exchange heat with each other. The high-temperature heat exchange channels are located in the high-temperature heat exchange circuit (10), and the low-temperature heat exchange channels are located in the low-temperature heat exchange circuit (20). The unit condenser and the unit evaporator are connected in the high-temperature heat exchange circuit (10) and the unit evaporator is connected in the low-temperature heat exchange circuit (20). The high-temperature heat exchange circuit (10) includes a high-temperature compressor (11), a first exhaust pipe (111), a first intake pipe (112), and a bypass pipe group (12). The first exhaust pipe (111) is connected between the outlet of the high-temperature compressor (11) and the unit condenser. The first intake pipe (112) is connected between the unit condenser and the intake of the high-temperature compressor (11). The first exhaust pipe (111) and the first intake pipe (112) are connected through the bypass pipe group (12). The bypass pipe group (12) is arranged in parallel with the unit condenser.

2. The cryogenic cascade unit according to claim 1, characterized in that, The bypass pipe assembly (12) includes an exhaust bypass pipe (121) and an intake bypass pipe (122). One end of the exhaust bypass pipe (121) is connected to the first exhaust pipe (111), and the other end is connected to the intake bypass pipe (122). The intake bypass pipe (122) is connected to the first intake pipe (112). A first switch (1211) is provided on the exhaust bypass pipe (121).

3. The cryogenic cascade unit according to claim 2, characterized in that, The high-temperature heat exchange circuit (10) further includes a first liquid reservoir (13) and a first liquid supply pipe (131). The unit condenser is connected to the first liquid reservoir (13), and the first liquid reservoir (13) is connected to the high-temperature heat exchange channel through the first liquid supply pipe (131). The bypass pipe group (12) further includes a first liquid reservoir bypass pipe (123). One end of the first liquid reservoir bypass pipe (123) is connected to the first liquid supply pipe (131), and the other end is connected to the suction bypass pipe (122). The first liquid reservoir bypass pipe (123) and the exhaust bypass pipe (121) converge and mix in the suction bypass pipe (122).

4. The cryogenic cascade unit according to claim 3, characterized in that, The first reservoir bypass pipe (123) is provided with a first throttling element (1231) and a first temperature sensing control element. The first throttling element (1231) is configured to change its opening degree in response to the control of the first temperature sensing control element.

5. The cryogenic cascade unit according to claim 3 or 4, characterized in that, The high-temperature heat exchange circuit (10) includes a first oil separator (14) and a first oil separator exhaust pipe (142) connected to the first oil separator (14). The first exhaust pipe (111) is connected to the unit condenser through the first oil separator (14) and the first oil separator exhaust pipe (142). The high-temperature heat exchange circuit (10) further includes a first balance pipe (15), one end of which is connected to the first liquid reservoir (13), and the other end is connected to the exhaust pipe (142) of the first oil separator.

6. The cryogenic cascade unit according to claim 1, characterized in that, The low-temperature heat exchange circuit (20) includes a low-temperature compressor (21), a second oil separator (22), a second oil separator exhaust pipe (221), a second liquid reservoir (23), and a second liquid reservoir drain pipe (231). The low-temperature compressor (21) is connected to the second oil separator (22). The second oil separator (22) is connected to the low-temperature heat exchange channel through the second oil separator exhaust pipe (221). The low-temperature heat exchange channel is connected to the second liquid reservoir drain pipe (231). The second liquid reservoir drain pipe (231) is connected to the second liquid reservoir (23).

7. The cryogenic cascade unit according to claim 6, characterized in that, The low-temperature heat exchange circuit (20) also includes a second liquid reservoir bypass pipe (232), one end of which is connected to the second liquid reservoir drain pipe (231), and the other end is connected to the second oil separator exhaust pipe (221).

8. The cryogenic cascade unit according to claim 7, characterized in that, A second switch (2321) is provided on the second reservoir bypass pipe (232), and a second temperature sensing element (2211) is provided on the second oil separator exhaust pipe (221). The second temperature sensing element (2211) can detect the temperature in the second oil separator exhaust pipe (221), and the second switch (2321) is configured to open or close in response to the triggering of the second temperature sensing element (2211).

9. The cryogenic cascade unit according to claim 1, characterized in that, The cryogenic cascade unit also includes a sustaining unit (30) and a sustaining heat exchanger (31). The sustaining heat exchanger (31) is provided with a third heat exchange channel and a fourth heat exchange channel. The third heat exchange channel and the fourth heat exchange channel are independent of each other and can exchange heat with each other. The sustaining unit (30) is connected to the third heat exchange channel. The cryogenic heat exchange circuit (20) includes a cryogenic compressor (21) and a second liquid receiver (23). The cryogenic compressor (21) is connected to the second liquid receiver (23), and the second liquid receiver (23) is connected to the fourth heat exchange channel.

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

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