Self-cascade refrigeration system and control method based on vortex tube regulation of working fluid composition and flow rate

Abstract

A self-cascade refrigeration system and control method based on vortex tube regulation of working fluid composition and flow rate are disclosed. The self-cascade refrigeration system includes a compressor, condenser, vortex tube, electronic expansion valve, solenoid valve, cascade heat exchanger, evaporator, control device, and temperature and pressure sensors. The control device collects signals from the compressor outlet pressure and temperature sensors, condenser outlet temperature sensor, vortex tube liquid phase outlet pressure sensor, vortex tube hot end outlet temperature sensor, and condenser outlet temperature sensor. It regulates the vortex tube hot end outlet regulating valve, electronic expansion valve, and control solenoid valve. During operation of the self-cascade refrigeration system, the regulating valve of the vortex tube adjusts the refrigerant flow rate in the evaporator, and the vortex tube outlet pressure changes the concentration of mixed working fluid components in the evaporator. By changing the refrigerant flow rate and mixed working fluid component concentration during operation, the safe and efficient operation of the refrigeration system is ensured, and the system's thermodynamic performance is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of cryogenic technology, specifically to a self-cascade refrigeration system and control method based on vortex tube adjustment of working fluid composition and flow rate. Background Technology

[0002] Currently, advancements in fields such as biomedicine and cryogenic technology have increased the demand for cooling temperatures below -40°C. Traditional vapor compression refrigeration systems or traditional absorption refrigeration systems experience a significant decrease in thermodynamic efficiency when achieving cooling temperatures below -40°C. Subsequently, cascade refrigeration systems emerged, employing two refrigeration systems connected in series. However, these systems face challenges such as increased complexity, difficulties in miniaturization, complex control strategies, and high investment costs. Self-cascade systems, on the other hand, utilize a single compressor and leverage the cascade heat transfer effect between mixed working fluids to achieve the required cooling temperature range. Furthermore, they offer advantages in terms of system investment costs.

[0003] The main process of a self-cascade system involves installing a gas-liquid separator at the condenser outlet. Utilizing the component shift behavior between phases, it separates the working fluid into a liquid phase rich in high-boiling points and a gas phase rich in low-boiling points. No energy exchange occurs during the gas-liquid two-phase separation process; therefore, there are significant heat transfer losses between the fluids within the cascade heat exchanger, as well as substantial losses within the throttling device. Therefore, to reduce these losses, it is necessary to reduce the concentration of the gas phase working fluid at the inlet of the cascade heat exchanger. Summary of the Invention

[0004] To address the shortcomings and deficiencies of the existing technology, this invention proposes a self-cascade refrigeration system and control method based on vortex tube regulation of working fluid composition and flow rate. This self-cascade refrigeration system replaces the gas-liquid separator with a vortex tube. The fluid at the condenser outlet is cooled and depressurized within the nozzle of the vortex tube, and then separated into low-temperature saturated gas, low-temperature saturated liquid, and high-temperature superheated gas within the main tube of the vortex tube. The low-temperature saturated gas enters the cascade heat exchanger for cooling, while the low-temperature saturated liquid, after throttling, provides cooling capacity to the cascade heat exchanger. This reduces irreversible heat exchange losses within the cascade heat exchanger and losses during the throttling process. Utilizing the energy separation characteristics of the vortex tube, a portion of the heat from the gaseous working fluid is transferred to the condenser, thus improving the system's energy efficiency and reducing system losses.

[0005] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0006] This invention proposes a self-cascade refrigeration system based on vortex tube regulation of working fluid composition and flow rate, comprising a compressor, wherein the compressor outlet pipe is connected to the inlet of a first condenser; the outlet of the first condenser is connected to the inlet nozzle of the vortex tube; the cold end outlet of the vortex tube main body is connected to the hot end inlet of a cascade heat exchanger; the hot end outlet of the cascade heat exchanger is connected to the inlet of a first electronic expansion valve; the outlet of the first electronic expansion valve is connected to the inlet of an evaporator; the liquid phase outlet of the vortex tube is connected to the inlet of a second electronic expansion valve; the outlet of the second electronic expansion valve and the evaporator outlet are combined and connected to the cold end inlet of the cascade heat exchanger; the hot end outlet of the vortex tube main body is connected to the inlet of a second condenser; the outlet of the second condenser and the cold end outlet of the cascade heat exchanger are combined and connected to the compressor inlet; and the input end of a control device is connected to the compressor. The first pressure sensor and the first temperature sensor at the outlet are connected; the input terminal of the control device is connected to the second temperature sensor at the condenser outlet; the input terminal of the control device is connected to the third temperature sensor at the hot end outlet of the main tube of the vortex tube; the input terminal of the control device is connected to the second pressure sensor at the liquid phase outlet of the vortex tube; the input terminal of the control device is connected to the fourth temperature sensor at the evaporator outlet; the output terminal of the control device is connected to the control mechanism of the compressor; the output terminal of the control device is connected to the regulating valve at the hot end outlet of the main tube of the vortex tube; the output terminal of the control device is connected to the control mechanism of the solenoid valve located between the outlet of the first condenser and the hot end inlet of the cascade heat exchanger; the output terminal of the control device is connected to the regulating mechanisms of the first electronic expansion valve, the second electronic expansion valve, and the third electronic expansion valve. During operation, the regulating valve at the hot end outlet of the main tube of the vortex tube can be adjusted to control the refrigerant flow rate into the evaporator, and the first, second, and third electronic expansion valves at the outlet of the vortex tube can be adjusted to control the outlet pressure of the vortex tube, thereby regulating the concentration of the mixed working fluid components in the evaporator and maintaining the efficient operation of the refrigeration system.

[0007] The cascade refrigeration system uses a binary non-azeotropic mixture as its working fluid. The high-temperature, high-pressure gas, compressed by the compressor, enters the condenser and then the nozzle of the vortex tube, where it is cooled and depressurized. Subsequently, the two-phase mixture at the nozzle outlet separates within the main tube. The liquid phase, rich in the high-boiling-point working fluid, exits from the liquid phase outlet of the vortex tube. The low-temperature gas, rich in the low-boiling-point working fluid, exits from the cold end outlet of the main tube of the vortex tube. The high-temperature gas, rich in the high-boiling-point working fluid, exits from the hot end outlet of the main tube of the vortex tube. The low-temperature gas then enters the hot end inlet of the cascade heat exchanger... The liquid is cooled to a subcooled state in the cascade heat exchanger; then, the subcooled liquid is cooled and depressurized in the first electronic expansion valve and enters the evaporator to absorb heat; the liquid phase fluid at the liquid phase outlet of the vortex tube enters the second electronic expansion valve to cool and depressurize, and the fluid at the outlet of the second electronic expansion valve mixes with the fluid at the outlet of the evaporator and enters the cold end inlet of the cascade heat exchanger; it absorbs heat and rises in temperature in the cascade heat exchanger; the high-temperature gas at the hot end outlet of the main tube of the vortex tube 3 is cooled in the second condenser, and then depressurized through the third electronic expansion valve, and then mixes with the fluid at the cold end outlet of the cascade heat exchanger and enters the compressor inlet.

[0008] During the startup phase of the self-cascade refrigeration system, the control device opens the solenoid valve; the two-phase fluid from the outlet of the first condenser enters the cascade heat exchanger for cooling; the fluid from the hot end outlet of the cascade heat exchanger enters the first electronic expansion valve for cooling and depressurization; the fluid from the outlet of the first electronic expansion valve enters the evaporator for heat absorption; the fluid from the outlet of the evaporator enters the cascade heat exchanger for heat absorption and temperature increase before entering the compressor; this solves the problem of high compressor startup pressure during the startup phase of the self-cascade refrigeration system; after the compressor starts up, the control device closes the solenoid valve, and the two-phase fluid from the outlet of the first condenser enters the nozzle of the vortex tube.

[0009] The control method for a self-cascade refrigeration system based on vortex tube regulation of working fluid composition and flow rate includes: the control device of the self-cascade refrigeration system collects signals from pressure and temperature sensors within the refrigeration system, as well as system operation time signals; the control device controls the on / off state of solenoid valves; the control device controls the start / stop of the compressor; and the control valve and third electronic expansion valve at the hot end outlet of the main tube of the vortex tube are adjusted to ensure stable operation of the refrigeration system; the compressor outlet safety pressure is P10 with a deviation of Δ10; the compressor outlet safety temperature is T10 with a deviation of Δ11; the evaporator outlet temperature setpoint is T40 with a deviation of Δ40; and the start-up time is t0. The control method is as follows:

[0010] 1) The control device collects the operating time t of the refrigeration system. When t < t0, the refrigeration system is in the startup phase, and the control device receives the pressure signal P1 from the first pressure sensor at the compressor outlet. The control device controls the control mechanism of the solenoid valve to open the solenoid valve, and the two-phase fluid at the outlet of the first condenser enters the cascade heat exchanger through the solenoid valve. The control device adjusts the opening degree of the first electronic expansion valve by controlling the adjustment mechanism of the first electronic expansion valve, so that P1 < P10 + Δ10;

[0011] 2) The control device collects the operating time t of the refrigeration system and the temperature signal T4 from the fourth temperature sensor at the evaporator outlet. When t ≥ t0 and T4 > T40 - Δ40, the refrigeration system is in the low-temperature pulling phase. The control device controls the control mechanism of the solenoid valve to close the solenoid valve. The control device adjusts the regulating valve at the hot end outlet of the main pipe of the vortex tube to reduce the opening degree of the regulating valve and increase the flow rate in the evaporator. The control device reduces the opening degrees of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve by controlling the adjustment mechanisms of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve, reduces the outlet pressure of the vortex tube, increases the concentration of low-boiling components in the evaporator, and collects the pressure signal P2 from the second pressure sensor. At this time, it is necessary to ensure that the temperature signal T3 of the third temperature sensor < T1, and ensure that the temperature signal T1 of the first temperature sensor at the outlet of the compressor 1 < T10 + Δ11;

[0012] 3) The control device collects the temperature signal T4 of the fourth temperature sensor at the evaporator outlet; when T40 - Δ40 ≤ T4 ≤ T40 + Δ40, the refrigeration system is in the stable operation stage; the control device collects the temperature signal T2 of the second temperature sensor at the outlet of the first condenser; when the change of the external environmental temperature causes the change of T2, when T2 increases, the control device controls the regulating mechanisms of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve to reduce the opening degrees of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve, reduce the outlet pressure of the vortex tube, increase the concentration of low-boiling components in the evaporator, and it is necessary to ensure that the temperature signal T3 of the third temperature sensor < T1, ensure that the temperature signal T1 of the first temperature sensor at the compressor outlet < T10 + Δ11, and ensure that T40 - Δ40 ≤ T4 ≤ T40 + Δ40; when T2 decreases, the control device controls the regulating mechanisms of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve to increase the opening degrees of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve, increase the outlet pressure of the vortex tube, reduce the concentration of low-boiling components in the evaporator, and it is necessary to ensure that the temperature signal T3 of the third temperature sensor < T1, ensure that the temperature signal T1 of the first temperature sensor at the compressor outlet < T10 + Δ11, and ensure that T40 - Δ40 ≤ T4 ≤ T40 + Δ40; when the set value T40 of the evaporator outlet temperature changes, when T40 increases, the control device controls the regulating mechanisms of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve to increase the opening degrees of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve, increase the outlet pressure of the vortex tube, and reduce the concentration of low-boiling components in the evaporator; the control device adjusts the hot-end outlet regulating valve of the main tube of the vortex tube to increase the opening degree of the hot-end outlet regulating valve and reduce the flow rate at the cold-end outlet of the main tube of the vortex tube; when T40 decreases, the control device controls the regulating mechanisms of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve to reduce the opening degrees of the first electronic expansion valve, the second electronic expansion valve and the third electronic expansion valve, reduce the outlet pressure of the vortex tube, increase the concentration of low-boiling components in the evaporator, and it is necessary to ensure that the temperature signal T3 of the third temperature sensor < T1, ensure that the temperature signal T1 of the first temperature sensor at the compressor outlet < T10 + Δ11; the control device adjusts the hot-end outlet regulating valve of the main tube of the vortex tube to reduce the opening degree of the hot-end outlet regulating valve and increase the flow rate at the cold-end outlet of the main tube of the vortex tube.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. Considering the large exergy loss of the cascade heat exchanger and the throttling device inside the self-cascade refrigeration system, using the energy separation characteristic of the vortex tube to reduce the exergy at the inlet of the cascade heat exchanger and the exergy at the inlet of the electronic expansion valve, thereby reducing the exergy loss of the cascade heat exchanger and the throttling device;

[0015] 2. By utilizing the energy separation characteristics of vortex tubes, an additional condenser is added to cool the high-temperature gas phase, thereby reducing the temperature in the gas phase rich in low-boiling-point components, increasing the system's cooling capacity, and thus improving the system's thermodynamic performance.

[0016] 3. The regulating valve at the hot end outlet of the vortex tube main tube can adjust the flow rate in the evaporator according to the operating conditions of the self-cascade refrigeration system. At the same time, it can adjust the pressure at the outlet of the vortex tube nozzle to regulate the component concentration of the mixed working fluid in the evaporator, so as to meet the high-efficiency operation of the refrigeration system under different operating conditions. Attached Figure Description

[0017] Figure 1 This is a flowchart of the self-cascade refrigeration system based on vortex tube adjustment of working fluid composition and flow rate as described in this invention.

[0018] 1. Compressor; 2. First condenser; 3. Swirl tube; 301. Nozzle; 302. Main tube; 303. Liquid phase outlet; 304. Regulating valve; 4. Second condenser; 5. Cascade heat exchanger; 6. Evaporator; 7. First electronic expansion valve; 8. Second electronic expansion valve; 9. Third electronic expansion valve; 10. Solenoid valve; 11. Control device; 101. First pressure sensor; 102. First temperature sensor; 103. Second temperature sensor; 104. Third temperature sensor; 105. Second pressure sensor; 106. Fourth temperature sensor. Detailed Implementation

[0019] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and an embodiment. It should be understood that the embodiment described herein is only for explaining the invention and is not intended to limit the invention.

[0021] Implementation Cases

[0022] like Figure 1As shown, a self-cascade refrigeration system based on vortex tube regulation of working fluid composition and flow rate includes a compressor 1. The outlet pipe of the compressor 1 is connected to the inlet of a first condenser 2. The outlet of the first condenser 2 is connected to the inlet nozzle 301 of a vortex tube 3. The cold end outlet of the main tube 302 of the vortex tube 3 is connected to the hot end inlet of a cascade heat exchanger 5. The hot end outlet of the cascade heat exchanger 5 is connected to the inlet of a first electronic expansion valve 7. The outlet of the first electronic expansion valve 7 is connected to the inlet of an evaporator 6. The liquid phase outlet 303 of the vortex tube 3 is connected to the inlet of a second electronic expansion valve 8. The outlet of the second electronic expansion valve 8 and the outlet of the evaporator 6 are combined and then connected to the cold end inlet of the cascade heat exchanger 5. The hot end outlet of the main tube 302 of the vortex tube 3 is connected to the inlet of a second condenser 4. The outlet of the second condenser 4 and the cold end outlet of the cascade heat exchanger 5 are combined and then connected to the compressor inlet. The input end of the control device 11 is connected to the compressor outlet first pressure sensor 101 and the second... A temperature sensor 102 is connected; the input terminal of the control device 11 is connected to the second temperature sensor 103 at the outlet of the condenser 2; the input terminal of the control device 11 is connected to the third temperature sensor 104 at the hot end outlet of the main tube 302 of the vortex tube 3; the input terminal of the control device 11 is connected to the second pressure sensor 105 at the outlet of the liquid phase outlet 303 of the vortex tube 3; the input terminal of the control device 11 is connected to the fourth temperature sensor 106 at the outlet of the evaporator 6; the output terminal of the control device 11 is connected to the control mechanism of the compressor 1; the output terminal of the control device 11 is connected to the regulating valve 304 at the hot end outlet of the main tube 302 of the vortex tube 3; the output terminal of the control device 11 is connected to the regulating mechanism of the first electronic expansion valve 7, the second electronic expansion valve 8, and the third electronic expansion valve 9; the output terminal of the control device 11 is connected to the control mechanism of the solenoid valve 10 located between the outlet of the first condenser 2 and the hot end inlet of the cascade heat exchanger 5.

[0023] The working process of the self-cascade refrigeration system based on vortex tube adjustment of working fluid composition and flow rate described in this invention is as follows: Figure 1As shown, the self-cascade refrigeration system uses a binary non-azeotropic mixture. The high-temperature, high-pressure gas, compressed by compressor 1, enters condenser 2 and then nozzle 301 of vortex tube 3, where it is cooled and depressurized. Subsequently, the two-phase mixture at the nozzle 301 outlet separates within the main tube 302. The liquid phase, rich in high-boiling-point working fluid, exits from the liquid phase outlet 303 of vortex tube 3. The low-temperature gas, rich in low-boiling-point working fluid, exits from the cold end outlet of the main tube 302 of vortex tube 3. The high-temperature gas, rich in high-boiling-point working fluid, exits from the hot end outlet of the main tube 302 of vortex tube 3. The low-temperature gas then enters cascade heat exchanger 5. The hot end inlet of the vortex tube 3 cools the liquid to a subcooled state in the cascade heat exchanger 5; then the subcooled liquid is cooled and depressurized in the first electronic expansion valve 7 and enters the evaporator 6 to absorb heat; the liquid phase fluid from the liquid phase outlet 303 of the vortex tube 3 enters the second electronic expansion valve 8 to cool and depressurize, and the fluid from the outlet of the second electronic expansion valve 8 mixes with the fluid from the outlet of the evaporator 6 and enters the cold end inlet of the cascade heat exchanger 5; it absorbs heat and rises in temperature in the cascade heat exchanger 5; the high temperature gas from the hot end outlet of the main tube 302 of the vortex tube 3 is cooled in the second condenser 4, and then depressurized by the third electronic expansion valve 9 and mixes with the fluid from the cold end outlet of the cascade heat exchanger 5 before entering the compressor 1 inlet.

[0024] The present invention discloses a control method for a self-cascade refrigeration system based on vortex tube adjustment of working fluid composition and flow rate. The input terminals of the control device 11 of the refrigeration system are connected to the first pressure sensor 101 and the first temperature sensor 102 at the outlet of compressor 1; the input terminal of the control device 11 is connected to the second temperature sensor 103 at the outlet of condenser 2; the input terminal of the control device 11 is connected to the third temperature sensor 104 at the hot end outlet of the main tube 302 of vortex tube 3; the input terminal of the control device 11 is connected to the second pressure sensor 105 at the outlet of the liquid phase outlet 303 of vortex tube 3; the input terminal of the control device 11 is connected to the fourth temperature sensor 106 at the outlet of evaporator 6; the output terminal of the control device 11 is connected to the control mechanism of compressor 1; the output terminal of the control device 11 is connected to the regulating valve 304 at the hot end outlet of the main tube 302 of vortex tube 3; the output terminal of the control device 11 is connected to the regulating mechanisms of the first electronic expansion valve 7, the second electronic expansion valve 8, and the third electronic expansion valve 9; and the output terminal of the control device 11 is connected to the control mechanism of solenoid valve 10. The control device 11 collects signals from the pressure and temperature sensors within the refrigeration system, along with the system's operating time signal. The control device 11 controls the opening and closing of the solenoid valve 10, and controls the start and stop of the compressor 1. It also adjusts the regulating valve 304 and the third electronic expansion valve 9 at the hot end outlet of the main tube 302 of the vortex tube 3 to ensure stable operation of the refrigeration system. The compressor outlet safety pressure P10 is 2.8 MPa, with a deviation value Δ10 of 0.02 MPa; the compressor outlet safety temperature T10 is 125℃, with a deviation value Δ11 of 2℃; the evaporator outlet temperature setpoint T40 is -60℃, with a deviation value Δ40 of 1℃; the start-up time is t0, which is 30 minutes. The control method is as follows:

[0025] 1) Control device 11 collects the running time t of the refrigeration system. When t < 30 min, the refrigeration system is in the start-up stage. Control device 11 receives the pressure signal P1 from the first pressure sensor 101 at the outlet of compressor 1. Control device 11 controls the control mechanism of solenoid valve 10 to open solenoid valve 10. The two-phase fluid at the outlet of the first condenser 2 enters the cascade heat exchanger 5 through solenoid valve 10. Control device 11 adjusts the opening degree of the first electronic expansion valve 7 by controlling the adjustment mechanism of the first electronic expansion valve 7 so that P1 < 2.82 MPa.

[0026] 2) The control device 11 collects the operating time t of the refrigeration system and the temperature signal T4 of the fourth temperature sensor 106 at the outlet of the evaporator 6. When t≥30 min and T4 > -61°C, the refrigeration system is in the low-temperature pulling stage. The control device 11 controls the control mechanism of the solenoid valve 10 to close the solenoid valve 10. The control device 11 adjusts the regulating valve 304 at the hot end outlet of the main pipe 302 of the vortex tube 3, reduces the opening degree of the regulating valve 304, and the adjustment step is 5%. The control device 11 controls the regulating mechanisms of the first electronic expansion valve 7, the second electronic expansion valve 8, and the third electronic expansion valve 9 to reduce the opening degrees of the first electronic expansion valve 7, the second electronic expansion valve 8, and the third electronic expansion valve 9, and the adjustment step is 5%, and collects the pressure signal P2 of the second pressure sensor 105. At this time, it is necessary to ensure that the temperature signal T3 of the third temperature sensor 104 < T1, and ensure that the temperature signal T1 of the first temperature sensor at the compressor outlet < 127°C;

[0027] 3) The control device 11 collects the temperature signal T4 of the fourth temperature sensor 106 at the outlet of the evaporator 6. When -61°C ≤ T4 ≤ -59°C, the refrigeration system is in the stable operation stage. The control device 11 collects the temperature signal T2 of the second temperature sensor 103 at the outlet of the first condenser 2. When the change of the external environmental temperature causes the change of T2, when T2 increases by 2°C each time, the control device 11 controls the regulating mechanisms of the first electronic expansion valve 7, the second electronic expansion valve 8, and the third electronic expansion valve 9 to reduce the opening degrees of the first electronic expansion valve 7, the second electronic expansion valve 8, and the third electronic expansion valve 9, and the step is 5%. It is necessary to ensure the temperature signal T3 of the third temperature sensor 104

Claims

1. A self-cascade refrigeration system based on vortex tube regulation of working fluid composition and flow rate, characterized in that, The system includes a compressor (1), whose outlet pipe is connected to the inlet of the first condenser (2); the outlet of the first condenser (2) is connected to the inlet nozzle (301) of the vortex tube (3); the cold end outlet of the main tube (302) of the vortex tube (3) is connected to the hot end inlet of the cascade heat exchanger (5); the hot end outlet of the cascade heat exchanger (5) is connected to the inlet of the first electronic expansion valve (7); the outlet of the first electronic expansion valve (7) is connected to the inlet of the evaporator (6); the liquid phase outlet (303) of the vortex tube (3) is connected to the inlet of the second electronic expansion valve (8); the outlet of the second electronic expansion valve (8) and the outlet of the evaporator (6) are combined and connected to the cascade heat exchanger (5). The cold end inlet of the vortex tube (3) is connected to the inlet of the second condenser (4); the hot end outlet of the main tube (302) of the vortex tube (3) is connected to the inlet of the second condenser (4); the outlet of the second condenser (4) is connected to the inlet of the third electronic expansion valve (9), and the outlet of the third electronic expansion valve (9) is combined with the cold end outlet of the cascade heat exchanger (5) and connected to the compressor inlet; the input end of the control device (11) is connected to the first pressure sensor (101) and the first temperature sensor (102) at the compressor outlet; the input end of the control device (11) is connected to the second temperature sensor (103) at the outlet of the condenser (2); the input end of the control device (11) is connected to the main tube (302) of the vortex tube (3) 02) The third temperature sensor (104) at the hot end outlet is connected; the input end of the control device (11) is connected to the second pressure sensor (105) at the liquid phase outlet (303) of the vortex tube (3); the input end of the control device (11) is connected to the fourth temperature sensor (106) at the outlet of the evaporator (6); the output end of the control device (11) is connected to the control mechanism of the compressor (1); the output end of the control device (11) is connected to the regulating valve (304) at the hot end outlet of the main tube (302) of the vortex tube (3); the output end of the control device (11) is connected to the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (7). The expansion valve (9) is connected to the regulating mechanism; the output end of the control device (11) is connected to the control mechanism of the solenoid valve (10) located between the outlet of the first condenser (2) and the hot end inlet of the cascade heat exchanger (5); during operation, the refrigeration system controls the refrigerant flow rate into the evaporator (6) by regulating the regulating valve (304) at the hot end outlet of the main tube (302) of the vortex tube (3), and controls the outlet pressure of the vortex tube (3) by regulating the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9) at the outlet of the vortex tube (3), thereby regulating the concentration of mixed working fluid components in the evaporator (6) and maintaining the efficient operation of the refrigeration system; During the startup phase of the self-cascade refrigeration system, the control device (11) controls the control mechanism of the solenoid valve (10) to open the solenoid valve (10); the two-phase fluid at the outlet of the first condenser (2) enters the cascade heat exchanger (5) for cooling; the fluid at the hot end outlet of the cascade heat exchanger (5) enters the first electronic expansion valve (7) for cooling and pressure reduction; the fluid at the outlet of the first electronic expansion valve (7) enters the evaporator (6) for heat absorption; the fluid at the outlet of the evaporator (6) enters the cascade heat exchanger (5) for heat absorption and temperature increase before entering the compressor (1); this solves the problem of high startup pressure of the compressor (1) during the startup phase of the self-cascade refrigeration system; after the compressor (1) starts up, the control device (11) controls the control mechanism of the solenoid valve (10) to close the solenoid valve (10), and the two-phase fluid at the outlet of the first condenser (2) enters the nozzle (301) of the vortex tube (3).

2. The self-cascade refrigeration system based on vortex tube regulation of working fluid composition and flow rate according to claim 1, characterized in that, The self-cascade refrigeration system uses a binary non-azeotropic mixture. The high-temperature, high-pressure gas compressed by the compressor (1) enters the condenser (2) and then enters the nozzle (301) of the vortex tube (3), where it is cooled and depressurized. After that, the two-phase mixture at the outlet of the nozzle (301) separates in the main tube (302). The liquid phase is discharged from the liquid phase outlet (303) of the vortex tube (3), and the liquid phase is rich in high-boiling-point working fluid. The low-temperature gas is discharged from the cold end outlet of the main tube (302) of the vortex tube (3), and the low-temperature gas is rich in low-boiling-point working fluid. The high-temperature gas is discharged from the hot end outlet of the main tube (302) of the vortex tube (3), and the high-temperature gas is rich in high-boiling-point working fluid. The low-temperature gas enters the hot end of the cascade heat exchanger (5). The liquid is cooled to a subcooled state in the cascade heat exchanger (5); then the subcooled liquid is cooled and depressurized in the first electronic expansion valve (7) and enters the evaporator (6) to absorb heat; the liquid phase fluid at the liquid phase outlet (303) of the vortex tube (3) enters the second electronic expansion valve (8) to cool and depressurize, and the fluid at the outlet of the second electronic expansion valve (8) mixes with the fluid at the outlet of the evaporator (6) and enters the cold end inlet of the cascade heat exchanger (5); it absorbs heat and rises in temperature in the cascade heat exchanger (5); the high temperature gas at the hot end outlet of the main tube (302) of the vortex tube (3) is cooled in the second condenser (4), and then depressurized through the third electronic expansion valve (9), and then mixes with the fluid at the cold end outlet of the cascade heat exchanger (5) and enters the compressor (1) inlet.

3. The control method for a self-cascade refrigeration system based on vortex tube adjustment of working fluid composition and flow rate as described in claim 1 or 2, characterized in that, The control device (11) of the self-cascade refrigeration system collects signals from the pressure sensor and temperature sensor in the refrigeration system and the system operation time signal. The control device (11) controls the opening and closing of the solenoid valve (10), controls the start and stop of the compressor (1), and adjusts the regulating valve (304) and the third electronic expansion valve (9) at the hot end outlet of the main tube (302) of the vortex tube (3) to ensure the stable operation of the refrigeration system. The compressor outlet safety pressure is P10 with a deviation value of Δ10; the compressor outlet safety temperature is T10 with a deviation value of Δ11; the evaporator outlet temperature setting value is T40 with a deviation value of Δ40; the start time is t0; the control method is as follows: 1) The control device (11) collects the operating time t of the refrigeration system. When t < t0, the refrigeration system is in the startup stage, and the control device (11) receives the pressure signal P1 from the first pressure sensor (101) at the outlet of the compressor (1). The control device (11) controls the control mechanism of the solenoid valve (10) to open the solenoid valve (10), and the two-phase fluid at the outlet of the first condenser (2) enters the cascade heat exchanger (5) through the solenoid valve (10). The control device (11) adjusts the opening degree of the first electronic expansion valve (7) by controlling the adjustment mechanism of the first electronic expansion valve (7) so that P1 < P10 + Δ10; 2) The control device (11) collects the operating time t of the refrigeration system and the temperature signal T4 of the fourth temperature sensor (106) at the outlet of the evaporator (6). When t ≥ t0 and T4 > T40 - Δ40, the refrigeration system is in the low-temperature pulling stage. The control device (11) controls the control mechanism of the solenoid valve (10) to close the solenoid valve (10). The control device (11) adjusts the regulating valve (304) at the hot end outlet of the main pipe (302) of the vortex tube (3) to reduce the opening degree of the regulating valve (304) and increase the flow rate in the evaporator (6). The control device (11) reduces the opening degrees of the first electronic expansion valve (7), the second electronic expansion valve (8), and the third electronic expansion valve (9) by controlling the adjustment mechanisms of the first electronic expansion valve (7), the second electronic expansion valve (8), and the third electronic expansion valve (9), reduces the outlet pressure of the vortex tube (3), increases the concentration of low-boiling components in the evaporator (6), and collects the pressure signal P2 of the second pressure sensor (105). At this time, it is necessary to ensure that the temperature signal T3 of the third temperature sensor (104) < T1, and ensure that the temperature signal T1 of the first temperature sensor (102) at the outlet of the compressor (1) < T10 + Δ11; 3) The control device (11) collects the temperature signal T4 of the fourth temperature sensor (106) at the outlet of the evaporator (6); when T40 - Δ40 ≤ T4 ≤ T40 + Δ40, the refrigeration system is in a stable operation stage; the control device (11) collects the temperature signal T2 of the second temperature sensor (103) at the outlet of the first condenser (2); when the change of the external environmental temperature causes the change of T2, when T2 increases, the control device (11) controls the regulating mechanisms of the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9), reduces the opening degrees of the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9), reduces the outlet pressure of the vortex tube (3), and increases the concentration of low-boiling components in the evaporator (6). It is necessary to ensure that the temperature signal T3 of the third temperature sensor (104) < T1, ensure that the temperature signal T1 of the first temperature sensor (102) at the outlet of the compressor (1) < T10 + Δ11, and ensure that T40 - Δ40 ≤ T4 ≤ T40 + Δ40; when T2 decreases, the control device (11) controls the regulating mechanisms of the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9), increases the opening degrees of the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9), increases the outlet pressure of the vortex tube (3), and reduces the concentration of low-boiling components in the evaporator (6). It is necessary to ensure that the temperature signal T3 of the third temperature sensor (104) < T1, ensure that the temperature signal T1 of the first temperature sensor (102) at the outlet of the compressor (1) < T10 + Δ11, and ensure that T40 - Δ40 ≤ T4 ≤ T40 + Δ40; when the set value T40 of the evaporator outlet temperature changes, when T40 increases, the control device (11) controls the regulating mechanisms of the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9), increases the opening degrees of the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9), increases the outlet pressure of the vortex tube 3, and reduces the concentration of low-boiling components in the evaporator (6); the control device (11) adjusts the heat end outlet regulating valve (304) of the main pipe (302) of the vortex tube (3), increases the opening degree of the heat end outlet regulating valve (304), and reduces the flow rate at the cold end outlet of the main pipe (302) of the vortex tube (3); when T40 decreases, the control device (11) controls the regulating mechanisms of the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9), reduces the opening degrees of the first electronic expansion valve (7), the second electronic expansion valve (8) and the third electronic expansion valve (9), reduces the outlet pressure of the vortex tube (3), and increases the concentration of low-boiling components in the evaporator (6). It is necessary to ensure that the temperature signal T3 of the third temperature sensor (104) < T1, and ensure that the temperature signal T1 of the first temperature sensor (102) at the outlet of the compressor (1) < T10 + Δ11;The control device (11) adjusts the hot-end outlet regulating valve (304) of the main body tube (302) of the vortex tube (3), reducing the opening of the hot-end outlet regulating valve (304) and increasing the flow rate at the cold end outlet of the main body tube (302) of the vortex tube (3).

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