Refrigerating system for providing cooling capacity for liquid nitrogen temperature zone

Abstract

The invention discloses a refrigerating system for providing cooling capacity in a liquid nitrogen temperature zone. The refrigerating system comprises a compressor, a pre-cooling unit, a throttling valve and a cold end heat exchanger which are sequentially connected to form a liquid nitrogen throttling refrigerating unit. The pre-cooling unit comprises a first-stage pre-cooling heat exchanger and a second-stage pre-cooling heat exchanger which are arranged in series, the cooling capacity of the first-stage pre-cooling heat exchanger is provided by a refrigeration unit capable of providing the refrigeration temperature of 265-285K, and the cooling capacity of the second-stage pre-cooling heat exchanger is provided by a refrigeration unit capable of providing the refrigeration temperature of 190-220K. Compared with the traditional non-precooling working condition, the precooling at the inlet of the heat exchanger has the advantages that the high pressure is obviously reduced, the pressure ratio is small, and the cooling capacity is sufficient. The advantage is particularly obvious when the pre-cooling temperature is low. And a two-stage refrigeration mode is adopted, accurate control over the cooling capacity can be achieved, and the energy consumption of the system is reduced while it is guaranteed that the cooling capacity is sufficient. In addition, photovoltaic power is used for providing electric energy, the ice storage tank is adopted, and energy conservation and consumption reduction in the refrigeration process can be achieved through the electricity price peak-valley price difference.

Description

Technical Field

[0001] The invention relates to a cooling system, in particular to a refrigeration system that efficiently provides cooling capacity in a liquid nitrogen temperature zone. Background Art

[0002] With the rapid development of my country's industry and technology, the demand for low-temperature environments is also increasing. Liquid nitrogen, as an important cryogenic medium, is often used in booming cutting-edge technologies such as space probes, quantum computers and cryogenic semiconductors to ensure the stable operation of various radiation sensors and high-performance chips. Therefore, efficient refrigeration technology in the liquid nitrogen temperature zone is particularly important.

[0003] The energy consumption of liquid nitrogen refrigeration system is one of the key factors affecting the overall operating cost and environmental impact. Traditional liquid nitrogen refrigeration technology often has the problems of high energy consumption and low efficiency, which not only increases the operating cost but also puts a burden on the environment. In order to improve the overall performance of liquid nitrogen refrigeration system, research and development of efficient liquid nitrogen temperature zone refrigeration system has become a current technical hotspot.

[0004] The use of an efficient liquid nitrogen temperature zone refrigeration system can significantly reduce the compressor's pressure ratio, reduce energy consumption, and improve refrigeration efficiency. At the same time, by optimizing the precooling process, more stable and precise low-temperature control can be achieved to meet the requirements of high-precision scientific experiments and production processes. In addition, the use of renewable energy such as solar energy for precooling can help further reduce energy consumption, reduce carbon emissions, and meet the requirements of sustainable development.

[0005] In the field of superconducting applications, stable and reliable operation of the refrigeration system is a necessary condition for the realization of superconductivity. Using a refrigerator to cool can achieve the regulation of the refrigeration temperature, but the DC cooling method requires extremely high pressure ratio of the compressor. In this context, the design of a precooling system for the liquid nitrogen temperature zone refrigeration system is of great practical significance for reducing the high pressure and pressure ratio of the compressor, thereby improving the refrigeration efficiency of the liquid nitrogen temperature zone. Summary of the invention

[0006] The object of the present invention is to provide a refrigeration system for providing cooling capacity in a liquid nitrogen temperature zone, which can efficiently provide cooling capacity in the liquid nitrogen temperature zone while improving energy utilization efficiency and reducing operating costs.

[0007] A refrigeration system for providing cooling capacity in a liquid nitrogen temperature zone comprises a compressor, a precooling unit, a throttle valve and a cold end heat exchanger which are sequentially connected to form a liquid nitrogen throttling refrigeration unit; the precooling unit comprises a primary precooling heat exchanger and a secondary precooling heat exchanger which are arranged in series, wherein the cooling capacity of the primary precooling heat exchanger is provided by a refrigeration unit which can provide a refrigeration temperature of 265-285K, and the cooling capacity of the secondary precooling heat exchanger is provided by a refrigeration unit which can provide a refrigeration temperature of 190-220K.

[0008] Preferably, the cooling capacity of the primary precooling heat exchanger is provided by a refrigeration unit capable of providing a refrigeration temperature of 268-280 K. The cooling capacity of the secondary precooling heat exchanger is provided by a refrigeration unit capable of providing a refrigeration temperature of 200-220 K.

[0009] As an option, the cooling capacity of the primary precooling heat exchanger is provided by a refrigeration unit using water as the refrigeration medium. As an option, the refrigeration unit adopts a solar lithium bromide absorption refrigeration unit. It mainly includes a solar collector, an evaporator, a condenser, a generator, an absorber, a solution heat exchanger, etc.

[0010] Preferably, it also includes an intermediate heat exchanger for exchanging heat at the cold end of the solar lithium bromide absorption refrigeration unit, and the obtained cold energy is transported to the primary pre-cooling heat exchanger by means of the intermediate heat exchanger.

[0011] Preferably, the cold outputted by the solar lithium bromide absorption refrigeration unit is delivered to the primary precooling heat exchanger through the intermediate heat exchanger via the primary preheating circulation loop. During actual connection, the high temperature pipeline of the evaporator in the solar lithium bromide absorption refrigeration unit is connected to the low temperature pipeline of the intermediate heat exchanger, and the cold is delivered to the high temperature pipeline therein, and finally provided to the primary precooling heat exchanger via the primary preheating circulation loop connected thereto. In the primary preheating circulation loop, a pump, a flow meter, etc. are generally provided.

[0012] Of course, the primary preheating circulation loop can also be directly connected to the high-temperature pipeline of the evaporator in the solar lithium bromide absorption refrigeration unit. In this case, the intermediate heat exchanger can be omitted and the cold exchange can be directly realized.

[0013] As an option, the intermediate heat exchanger is a shell and tube heat exchanger.

[0014] As an option, the cooling capacity of the secondary pre-cooling heat exchanger is provided by a semiconductor refrigeration sheet.

[0015] As an option, the first-stage precooling heat exchanger and the second-stage precooling heat exchanger are plate heat exchangers.

[0016] The outlet of the shell and tube heat exchanger is connected to the inlet of the plate heat exchanger I through a pipeline. The ice storage tank is connected to the inlet of the flow valve through a pipeline, and the outlet of the flow valve is connected to the inlet of the plate heat exchanger I through a pipeline. The thermistor and the fixed resistor are connected to form a voltage divider circuit, the output end of the voltage divider circuit is connected to the input end of the operational amplifier, and the output end of the operational amplifier is connected to the TEC refrigeration sheet. The reference voltage set by the adjustable resistor is input to the in-phase input end of the operational amplifier. The output end of the photovoltaic module is connected to the power input end of the system to provide the electrical energy required for the operation of the system.

[0017] As an option, the primary preheating circulation loop also includes an ice storage tank and a flow valve arranged in parallel with the intermediate heat exchanger. When the electricity price is low, the water in the ice storage tank can be frozen into ice using electric energy to store energy and release cold energy during peak electricity price periods.

[0018] Furthermore, the ice storage tank is connected to the flow valve through a pipeline, and the outlet of the flow valve is connected to the low-pressure pipeline of the primary precooling heat exchanger (plate heat exchanger I) through a pipeline (the pipeline between the outlet of the flow valve and the primary precooling heat exchanger is provided with the pump, flow meter, etc.), providing additional cooling capacity to supplement the cooling capacity supply of the solar lithium bromide chiller. With this technical solution, during the low electricity price period, the system uses the ice storage tank to store cooling capacity to reduce energy consumption during the peak period, thereby achieving energy saving effect. The operation steps are as follows: During the low electricity price period, the low-temperature ethylene glycol aqueous solution in the ethylene glycol refrigeration circulation loop is introduced into the heat exchange pipeline of the ice storage tank, so that the water in the ice storage tank is frozen into ice to store cooling capacity. During the peak electricity price period, the medium in the primary preheating circulation loop is connected to the heat exchange pipeline of the ice storage tank, the ice storage tank releases cooling capacity, melts ice cubes, and transfers the cooling capacity of the primary preheating circulation loop to the primary precooling heat exchanger.

[0019] As an option, the throttling valve inlet pipeline and the cold end heat exchanger outlet pipeline exchange heat through a wall heat exchanger.

[0020] As an option, also include:

[0021] A temperature sensor for detecting the temperature of the nitrogen working fluid after secondary precooling;

[0022] The controller receives the temperature signal from the temperature sensor and controls the cooling capacity of the semiconductor refrigeration plate according to the temperature signal.

[0023] The temperature sensor (a thermistor may be selected) is used to detect the temperature of the nitrogen after secondary pre-cooling in real time, and convert the temperature signal into a voltage signal and transmit it to the control circuit to ensure that the temperature of the system can always be within the target range. If the temperature deviates from the set value, the system will automatically adjust the working state of the refrigeration plate to restore the target temperature.

[0024] Furthermore, the temperature sensor is a thermistor.

[0025] Also includes:

[0026] A voltage divider circuit having the thermistor and a fixed resistor connected in series;

[0027] A reference branch with an adjustable resistor is provided, the resistance value of the adjustable resistor is determined by the set target temperature of the secondary precooling;

[0028] The voltage dividing circuit and the reference branch are arranged in parallel;

[0029] The comparator receives the voltage signals of the voltage divider circuit and the reference branch, makes a judgment, and feeds the judgment information back to the controller.

[0030] The voltage divider circuit is responsible for converting temperature changes into voltage changes. The obtained voltage change signal is then input into a comparator for comparing the actual temperature with the target temperature, thereby providing basic data for subsequent temperature regulation.

[0031] The comparator (which may be an operational amplifier) ​​receives the voltage signal from the voltage divider circuit and compares it with the reference voltage of the reference branch (the target temperature set by the adjustable resistor); if the detected temperature deviates from the target temperature, the operational amplifier will output a corresponding signal to adjust the working state of the TEC cooling plate, thereby adjusting the system temperature.

[0032] The adjustable resistor is used to set the reference voltage of the operational amplifier, that is, the target temperature of the system. By adjusting the resistor, the operator can set the target temperature of the pre-cooling unit (e.g. 195K). This enables the system to adapt to different pre-cooling requirements and provide flexible temperature control.

[0033] The working state of the semiconductor refrigeration chip is controlled by the comparison result of the operational amplifier, and the cooling output can be adjusted according to the real-time temperature, thereby ensuring that the temperature of the nitrogen reaches the set value after the secondary pre-cooling. Its fast response capability enables the system to accurately control the temperature and prevent the temperature from being too low or too high.

[0034] The controller is the core processing unit of the entire control system, responsible for processing the data of each sensor, executing the predetermined control logic, and coordinating the work of each actuator. According to the feedback information from the sensor, the controller can automatically adjust the working status of components such as flow valves, pumps and TEC refrigeration sheets to ensure stable operation of the system. At the same time, the controller is also responsible for managing the switching of photovoltaic module power supply and the release of cold energy from the ice storage tank.

[0035] It also includes a power supply that provides electrical energy to the entire system;

[0036] Preferably, the power source is a photovoltaic module. The photovoltaic module can be used as the power supply part of the system, responsible for providing power to the entire control system and the TEC cooling plate. Using solar power reduces the system's external power dependence, making the system more energy-saving and environmentally friendly.

[0037] As a preferred embodiment, a thermometer is used to detect and display the temperature of the nitrogen working medium after the secondary precooling. The thermometer is used to detect and display the temperature of the working medium after the secondary precooling.

[0038] As a specific option, the comparator selects an operational amplifier.

[0039] Preferably, the power source adopts a photovoltaic module, which can provide power for the electrical components of the system, including but not limited to controllers, compressors, semiconductor cooling sheets, etc.

[0040] The technical solution adopted by the present invention to solve the above-mentioned problem is: a liquid nitrogen refrigeration system, including a compressor, a plate heat exchanger, a compression pump, a flow valve, an ice storage tank, a TEC refrigeration plate (i.e., a semiconductor refrigeration plate), a shell and tube heat exchanger, a thermistor, a fixed resistor, an adjustable resistor, an operational amplifier, a thermometer, a partition heat exchanger, a throttle valve, a flow meter, and a photovoltaic module.

[0041] The plate heat exchangers are provided with two, which are used as a primary precooling heat exchanger and a secondary precooling heat exchanger respectively, and are defined as plate heat exchanger I for further description.

[0042] The outlet of the compressor is connected to the high-pressure pipeline inlet of the plate heat exchanger I through a pipeline, so as to compress the nitrogen at room temperature and send it to the plate heat exchanger 1 for primary precooling; the high-pressure pipeline outlet of the plate heat exchanger I is connected to the high-pressure pipeline inlet of the plate heat exchanger II through a pipeline; the high-pressure pipeline outlet of the plate heat exchanger II is connected to the high-pressure pipeline inlet of the partition heat exchanger through a pipeline, and a thermometer and a temperature sensor are provided on the pipeline to detect the specific temperature value and temperature signal of the working medium after secondary precooling; the high-pressure pipeline outlet of the partition heat exchanger is connected to the inlet of the throttle valve through a pipeline; the outlet of the throttle valve is connected to the inlet of the cold-end heat exchanger through a pipeline; the outlet of the cold-end heat exchanger is connected to the low-pressure pipeline inlet of the partition heat exchanger through a pipeline, and the low-pressure pipeline outlet of the partition heat exchanger is connected to the compressor ring inlet through a pipeline.

[0043] Furthermore, the thermistor and the fixed resistor are connected to form a voltage divider circuit, the output end of the voltage divider circuit is connected to the input end of the operational amplifier, the output end of the operational amplifier is connected to the input end of the controller, and the output end of the controller is connected to the TEC cooling plate for monitoring and adjusting the system temperature; the reference voltage set by the adjustable resistor is input to the in-phase input end of the operational amplifier to set the target temperature; the output end of the photovoltaic module is connected to the power input end of the system to provide the power required for the operation of the system. During operation, the temperature change is converted into a voltage change through the voltage divider circuit composed of the thermistor and the fixed resistor, and the voltage divider signal is input to the operational amplifier. The operational amplifier compares the reference voltage (195K) set by the adjustable resistor with the actual temperature to control the working state of the TEC cooling plate.

[0044] Furthermore, the working fluid after secondary precooling is detected by a thermometer and a temperature sensor to determine whether it has reached the target temperature, and then enters the intermediate wall heat exchanger and the throttle valve to convert the nitrogen into a gas-liquid two-phase working fluid, releasing the coldness in the liquid nitrogen temperature zone.

[0045] The invention discloses a refrigeration system for a liquid nitrogen temperature zone, comprising a liquid nitrogen throttling refrigeration unit, a precooling unit and a corresponding control unit.

[0046] In the liquid nitrogen throttling refrigeration unit, including the compressor, cold end heat exchanger, throttle valve, etc., the precooling unit adopts a two-stage precooling method. The solar lithium bromide unit and the ice storage tank provide the first-stage cooling capacity through the plate heat exchanger, and the semiconductor refrigeration plate provides the second-stage cooling capacity through the control unit. In actual operation, the nitrogen compressed by the compressor first enters the first-stage precooling heat exchanger for the first-stage precooling, and then enters the second-stage precooling heat exchanger for the second-stage precooling. The control unit consists of a temperature sensor, a comparator, a controller and a TEC refrigerator.

[0047] Furthermore, the heat exchanger uses a plate heat exchanger.

[0048] The specific operation steps of the present invention are as follows:

[0049] (1) The compressor compresses nitrogen at room temperature, and the compressed nitrogen enters the plate heat exchanger I through a pipeline for primary pre-cooling; the cooling capacity is provided by the solar lithium bromide chiller components, namely the collector, evaporator, condenser and ice storage tank.

[0050] (2) The nitrogen after primary precooling enters plate heat exchanger II for secondary precooling. The temperature of the nitrogen after secondary precooling is detected by a thermometer. At the same time, the temperature of the precooled nitrogen is monitored by a voltage divider circuit composed of a thermistor and a fixed resistor, and the working state of the TEC cooling plate is controlled by an operational amplifier and an adjustable resistor.

[0051] (3) After secondary precooling, the nitrogen enters the partition heat exchanger through a pipeline, and then is converted into a gas-liquid two-phase working fluid through a throttle valve, releasing the cold energy in the liquid nitrogen temperature zone in the cold end heat exchanger, and the outlet is converted into nitrogen again for the next cycle.

[0052] (4) The solar collector absorbs solar energy and transfers heat to the evaporator. The evaporator uses the transferred heat to evaporate the working medium and generate cooling energy. The generated cooling energy is transferred to the condenser through the pipeline, where condensation and heat release are carried out. The condensed working medium enters the shell and tube heat exchanger through the pipeline for further heat exchange, providing stable primary cooling energy. It is transferred to the plate heat exchanger through the shell and tube heat exchanger, and completes the primary pre-cooling together with the plate heat exchanger and the ice storage tank.

[0053] (5) During the period of low electricity prices, the flow rate is controlled by the flow valve, and the low-temperature ethylene glycol water solution is introduced into the ice storage tank heat exchange pipeline, so that the water in the ice storage tank is frozen into ice and the cold energy is stored; during the period of peak electricity prices, the flow rate is controlled by the flow valve, the cold energy is released from the ice storage tank, the ice cubes are melted, and the cold energy is transferred to the secondary precooling heat exchanger to extract the cold energy for precooling.

[0054] (6) The electricity required for the entire process is provided by photovoltaic panels.

[0055] The control part of the refrigeration system of the present invention forms a closed-loop control system through the coordinated work of multiple components such as temperature sensor, voltage divider circuit, operational amplifier, adjustable resistor, TEC refrigeration sheet, controller, photovoltaic module, flow meter, flow valve, ice storage tank and thermometer. It can not only monitor and adjust the temperature in real time, but also realize the efficient and energy-saving operation of the system by reasonably allocating cooling capacity and electric energy resources. The role of each component in the control part is to ensure the stability, accuracy and energy efficiency optimization of the entire pre-cooling process.

[0056] Compared with the traditional working condition without precooling, the present invention can significantly reduce the high pressure of the heat exchanger inlet by precooling, and has the advantages of small pressure ratio and sufficient cooling capacity. This advantage is particularly obvious when the precooling temperature is low. The two-stage refrigeration method can achieve precise control of cooling capacity, while ensuring sufficient cooling capacity and reducing system energy consumption. In addition, by using photovoltaic power to provide electricity and using ice storage tanks to take advantage of the peak and valley price difference of electricity prices, energy saving and consumption reduction can be achieved in the refrigeration process.

[0057] The present invention is mainly used to efficiently provide cooling capacity in the liquid nitrogen temperature zone and has broad application prospects. It can not only provide a stable and reliable low-temperature environment for industrial cooling, scientific research, food cold chain, medical refrigeration, semiconductor manufacturing and other fields, but also promote the development of high-tech fields such as superconductor technology, and provide efficient and energy-saving low-temperature solutions for various industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is the overall structural diagram of the present invention;

[0059] In the figure: 1. compressor; 2. partition heat exchanger; 3. cold end heat exchanger; 4. throttle valve; 5. thermometer; 6. plate heat exchanger II; 7. plate heat exchanger I; 11-solar lithium bromide absorption refrigeration unit; 12-shell and tube heat exchanger; 13-ice storage tank; 14-flow valve; 15-ethylene glycol delivery pump 16-flow meter; 17-water circulation pump; 18-TEC refrigeration plate; 19-fin; 20-controller; 21-operational amplifier; 24-adjustable resistor; 22-fixed resistor; 23-thermistor; 25-photovoltaic module.

[0060] Figure 2 is the relationship curve between nitrogen inlet temperature and high pressure;

[0061] Figure 3 It is the relationship curve between temperature drop and cooling capacity of TEC refrigeration unit. DETAILED DESCRIPTION

[0062] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0063] See also Figure 1 A refrigeration system capable of providing cooling capacity in a liquid nitrogen temperature zone includes a compressor 1, a plate heat exchanger I 7, a plate heat exchanger II 6, a compression pump 15, a flow valve 14, an ice storage tank 13, a flow meter 16, a water circulation pump 17, a TEC refrigeration sheet 18, a fin 19, an intermediate heat exchanger 12, a thermistor 23, a fixed resistor 22, an adjustable resistor 24, an operational amplifier 21, a controller 20, a thermometer 5, a partition heat exchanger 2, a throttle valve 4, and a photovoltaic module 23.

[0064] The outlet of compressor 1 is connected to the inlet of the medium and high pressure pipeline (high temperature pipeline) of plate heat exchanger I 7 through a pipeline, so as to compress the nitrogen at normal temperature and send it into plate heat exchanger I 7 for primary precooling; the outlet of the medium and high pressure pipeline of plate heat exchanger I 7 is connected to the inlet of the medium and high pressure pipeline of plate heat exchanger II 6 through a pipeline, so as to be used for secondary precooling; the outlet of the medium and high pressure pipeline of plate heat exchanger II 6 is connected to the inlet of the medium and high pressure pipeline of partition type heat exchanger 2 through a pipeline, and a thermometer 5 is provided on the pipeline for detecting the nitrogen temperature after secondary precooling; the outlet of the medium and high pressure pipeline of partition type heat exchanger 2 is connected to the inlet of throttle valve 4 through a pipeline; the outlet of throttle valve 4 is connected to the inlet of cold end heat exchanger 3 through a pipeline, and the outlet of cold end heat exchanger 3 is connected to the inlet of system circulation compressor 1 through a pipeline.

[0065] The cooling capacity of the plate heat exchanger 17 is provided by a solar lithium bromide absorption refrigeration unit, which mainly includes a solar collector, an evaporator, a condenser, an absorber, a generator, a solution heat exchanger, etc. The cooling capacity generated by the evaporator in the lithium bromide absorption refrigeration unit is provided by a shell and tube heat exchanger 12, etc. The outlet of the cooled pipeline in the shell and tube heat exchanger 12 is connected to a water circulation pump 17 through a pipeline, and the outlet of the water circulation pump 17 is connected to the inlet of the medium and low pressure pipeline (low temperature pipeline) of the plate heat exchanger 17 through a pipeline to provide the cooling capacity required for the first stage precooling. A flow meter 16 is provided on the pipeline between the water circulation pump 17 and the inlet of the medium and low pressure pipeline of the plate heat exchanger 17 to control the flow rate of the chilled water working medium.

[0066] Another branch connected in parallel with the shell and tube heat exchanger 12 is composed of an ice storage tank 13, an ethylene glycol delivery pump 15, and a flow valve 14. The ice storage tank 13 is connected to the flow valve 14 through a pipeline, and the outlet of the flow valve 14 is connected to the water circulation pump 17 through a pipeline, and the outlet of the water circulation pump 17 is connected to the inlet of the medium and low pressure pipeline of the plate heat exchanger I 7 through a pipeline to provide additional cooling capacity to supplement the cooling capacity supply of the solar lithium bromide absorption refrigeration unit; a flow meter 16 is provided on the pipeline between the water circulation pump 17 and the inlet of the medium and low pressure pipeline of the plate heat exchanger I 7 to control the flow of the chilled water working medium.

[0067] In the control circuit of the TEC cooling plate, the thermistor 23 and the fixed resistor 22 are connected to form a voltage divider circuit, the output end of the voltage divider circuit is connected to the input end of the operational amplifier 21, the output end of the operational amplifier is connected to the controller 20, and the output end of the controller 20 is connected to the TEC cooling plate 18 for monitoring and adjusting the system temperature; the reference voltage set by the adjustable resistor 24 is input to the in-phase input end of the operational amplifier to set the target temperature; the hot end of the TEC cooling plate 18 is provided with a heat sink fin 19 to promote heat dissipation at the hot end and ensure stable cooling capacity at the cold end; the output end of the photovoltaic module 25 is connected to the power input end of the system to provide the electrical energy required for the system operation.

[0068] The heat exchanger 3 uses a plate heat exchanger.

[0069] The chilled water supply pipe and the chilled water return pipe are connected to the end of the system to realize the cooling cycle.

[0070] This refrigeration system has been subjected to liquid nitrogen JT throttling refrigeration experiments in the early stage of design. The nitrogen flow rate is set to 0.7g / s, the initial inlet temperature is 300K, and the outlet low pressure is 0.1MPa. The inlet temperature of nitrogen working fluid of existing refrigerators is room temperature. The experimental results show that the inlet high pressure needs to reach 10MPa, so the compressor pressure ratio is required to be about 100. At present, there is no compressor with a pressure ratio that can reach this value. Therefore, it is considered to design a precooling system to reduce the temperature of the nitrogen inlet, in order to reduce the inlet pressure.

[0071] Through simulation calculation, such as Figure 2 As shown, there is an obvious linear relationship between high pressure and temperature. In order to achieve the refrigeration effect and take into account the economy of the system, the pre-cooling temperature range is set between 200K and 220K. The selection of this temperature range reduces the inlet high pressure of nitrogen from 10MPa to about 2.17 to 2.4MPa, and the low pressure is maintained at about 0.1MPa, thereby effectively reducing the pressure ratio. Under this pressure ratio condition, there are many types of compressors that can be selected, which can reduce system energy consumption while reducing equipment costs and improving system operation efficiency and reliability.

[0072] Considering the small flow rate of the system, in order to balance the heat exchange efficiency and the portability of the system, it was decided to use a combination of TEC refrigeration fins wrapped with plate heat exchangers for pre-cooling. In order to reduce the load of the TEC refrigeration fins and further optimize the cooling effect of the system, a primary refrigeration unit was added. Figure 3 The performance characteristics of the TEC refrigeration unit and the relationship between temperature drop and cooling capacity are shown. In actual operation, the first-stage precooling temperature is controlled at 273K. This temperature is chosen because it is close to the freezing point of water, which is convenient for achieving first-stage cooling through a small solar lithium bromide absorption refrigeration unit combined with an ice storage tank and a heat exchanger. At the same time, compared with other first-stage cooling temperatures, the temperature difference that can be achieved in the second-stage precooling is larger. The second-stage precooling temperature difference is set between 60K and 70K, and the precooling temperature is finally controlled within the range of 200K to 220K to achieve a better cooling effect. The cooling temperature of the system can be flexibly adjusted through the control system to adapt to different operating conditions.

[0073] The specific steps are as follows:

[0074] (1) Compressor 1 compresses nitrogen at room temperature, and the compressed nitrogen enters the plate heat exchanger I7 through a pipeline for primary precooling.

[0075] (2) The nitrogen after primary precooling enters the plate heat exchanger II 6 for secondary precooling. The temperature of the nitrogen after secondary precooling is detected and displayed by the thermometer 5. At the same time, the temperature signal of the nitrogen after secondary precooling is detected by the thermistor 23.

[0076] (3) After secondary precooling, the nitrogen enters the high-pressure pipeline of the partitioning heat exchanger 2 through a pipeline for further cooling, and then is converted into a gas-liquid two-phase working medium through a throttle valve 4, releasing the cold energy in the liquid nitrogen temperature zone in the cold end heat exchanger 3, and is converted into nitrogen again at the outlet for the next cycle.

[0077] (4) Solar lithium bromide absorption refrigeration unit will cool

[0078] The shell and tube heat exchanger 14 and the ice storage tank 13 provide bypass cooling capacity to jointly complete the primary precooling of nitrogen.

[0079] (5) During the period of low electricity prices, a low-temperature ethylene glycol aqueous solution is introduced into the ice storage tank 13 to freeze the water in the ice storage tank into ice and store cold energy. During the period of peak electricity prices, the flow rate is controlled by the flow valve 14 to release cold energy from the ice storage tank 13, melt the ice cubes, and transfer the cold energy to the water medium for cooling.

[0080] (6) The electric energy required for the whole process is provided by the photovoltaic module 25.

[0081] In this embodiment, the efficiency of the compressor and the heat exchanger can be further improved by adding a liquid nitrogen pre-cooling unit, and the heat loss of the system can be reduced by adopting a vacuum multi-layer insulation method; a modular design is introduced into the control system so that the system can intelligently monitor and optimize the temperature according to actual needs, thereby achieving further energy saving and consumption reduction of the refrigeration system.

[0082] The contents not described in detail in this specification belong to the prior art known to the professional and technical personnel in this field. The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes to the technical solutions and utility model concepts of the present invention within the technical scope disclosed by the present utility model, which should be covered by the protection scope of the present invention.

Claims

1. A refrigeration system that provides cooling capacity in the liquid nitrogen temperature zone, characterized in that: The invention comprises a compressor, a precooling unit, a throttle valve and a cold end heat exchanger which are sequentially connected to form a liquid nitrogen throttling refrigeration unit; the precooling unit comprises a first-stage precooling heat exchanger and a second-stage precooling heat exchanger which are arranged in series, wherein the cooling capacity of the first-stage precooling heat exchanger is provided by a refrigeration unit which can provide a refrigeration temperature of 265-285K, and the cooling capacity of the second-stage precooling heat exchanger is provided by a refrigeration unit which can provide a refrigeration temperature of 190-220K.

2. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 1, characterized in that: The cooling capacity of the primary precooling heat exchanger is provided by a refrigeration unit using water as the refrigeration medium.

3. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 1, characterized in that: The cooling capacity of the secondary pre-cooling heat exchanger is provided by semiconductor refrigeration sheets.

4. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 1, characterized in that: The first-stage precooling heat exchanger and the second-stage precooling heat exchanger are plate-type heat exchangers.

5. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 2, characterized in that: The refrigeration unit adopts a solar lithium bromide absorption refrigeration unit.

6. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 1, characterized in that: The throttle valve inlet pipeline and the cold end heat exchanger outlet pipeline exchange heat through a wall heat exchanger.

7. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 3, characterized in that: Also includes: A temperature sensor for detecting the temperature of the nitrogen working fluid after secondary precooling; a controller for receiving a temperature signal from the temperature sensor and controlling the cooling capacity of the semiconductor refrigeration plate according to the temperature signal.

8. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 7, characterized in that: The temperature sensor is a thermistor; Also includes: A voltage divider circuit having the thermistor and a fixed resistor connected in series; A reference branch with an adjustable resistor is provided, the resistance value of the adjustable resistor is determined by the set target temperature of the secondary precooling; The voltage dividing circuit and the reference branch are arranged in parallel; The comparator receives the voltage signals of the voltage divider circuit and the reference branch, performs comparison, and feeds back the comparison information to the controller.

9. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 5, characterized in that: It also includes an intermediate heat exchanger for exchanging heat at the cold end of the solar lithium bromide absorption refrigeration unit, and uses the intermediate heat exchanger to transmit the obtained cold energy to the first-stage pre-cooling heat exchanger; optionally, it also includes a flow valve and an ice storage tank arranged in parallel with the intermediate heat exchanger.

10. The refrigeration system for providing cooling capacity in the liquid nitrogen temperature zone according to claim 1, characterized in that: A thermometer used to detect and display the temperature of the nitrogen working fluid after secondary precooling.

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