CN111156756B - Self-adaptive charging amount adjusting system and control method in cooling process of ultralow temperature refrigerator - Google Patents

Self-adaptive charging amount adjusting system and control method in cooling process of ultralow temperature refrigerator Download PDF

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CN111156756B
CN111156756B CN202010062679.2A CN202010062679A CN111156756B CN 111156756 B CN111156756 B CN 111156756B CN 202010062679 A CN202010062679 A CN 202010062679A CN 111156756 B CN111156756 B CN 111156756B
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temperature
stage
expansion tank
low
refrigerant
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CN111156756A (en
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曹锋
王海丹
宋昱龙
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Xian Jiaotong University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D11/00—Self-contained movable devices, e.g. domestic refrigerators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B1/00—Compression machines, plants or systems with non-reversible cycle
    • F25B1/10—Compression machines, plants or systems with non-reversible cycle with multi-stage compression
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B40/00—Subcoolers, desuperheaters or superheaters
    • F25B40/06—Superheaters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B41/00—Fluid-circulation arrangements
    • F25B41/30—Expansion means; Dispositions thereof
    • F25B41/37—Capillary tubes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B45/00—Arrangements for charging or discharging refrigerant
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D17/00—Arrangements for circulating cooling fluids; Arrangements for circulating gas, e.g. air, within refrigerated spaces
    • F25D17/04—Arrangements for circulating cooling fluids; Arrangements for circulating gas, e.g. air, within refrigerated spaces for circulating air, e.g. by convection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D29/00—Arrangement or mounting of control or safety devices
    • F25D29/005—Mounting of control devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D29/00—Arrangement or mounting of control or safety devices
    • F25D29/008—Alarm devices

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  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Devices That Are Associated With Refrigeration Equipment (AREA)

Abstract

Compared with the traditional cascade type ultra-low temperature refrigerator refrigerating system, the system is additionally provided with a two-stage expansion tank-stop valve mechanism between a condensation evaporator and a low-temperature stage throttling capillary tube, and a two-stage electric heating device is arranged on the outer side of a tank body of the two-stage expansion tank. The system is to the incasement temperature at super low temperature refrigerator cooling in-process, the heat transfer difference in condensation evaporator department, low temperature level subsystem supercooling degree and high temperature level subsystem superheat degree monitor, control doublestage stop valve, the opening and closing of electrical heating mechanism, the refrigerant circulation volume of automatically regulated low temperature level subsystem in conventional scope, guarantee system cooling speed in cooling process earlier stage, and through the accurate lowering system evaporating temperature of opening and close of doublestage stop valve-expansion tank mechanism in the later stage of cooling, realize fast, the cooling effect of reinforceing, exceed the control range then and send corresponding trouble suggestion, the artifical high efficiency of being convenient for is solved the system and is filled the volume problem.

Description

Self-adaptive charging amount adjusting system and control method in cooling process of ultralow temperature refrigerator
Technical Field
The invention belongs to the technical field of refrigeration and low temperature, and particularly relates to a self-adaptive charging quantity adjusting system and a control method in a cooling process of an ultralow temperature refrigerator.
Background
Today, the world energy and environment are still two major focus of continuous world attention. With the remarkable improvement of the life quality of people, the demands of various industries on refrigeration technology are increasingly extensive, and a favorable opportunity is created for the development of the low-temperature refrigeration industry. At present, China enters the key period of economic development of transformation China, and new period, new situation and new development opportunity provide more strict development requirements for refrigeration technology related to the fields of modern low-temperature medical blood and organ preservation, high-quality food freezing, chemical reagent storage and the like. In this case, low temperature refrigerators of different temperature zones have been produced and developed rapidly. In order to create an ultra-low temperature refrigerator capable of obtaining a low temperature environment of-60 ℃ to-120 ℃, the cascade refrigeration system becomes a mainstream refrigeration mode of the low temperature refrigerator by virtue of the flexibility and reliability of a temperature zone.
Nowadays, various industries in China possess tens of thousands of low-temperature refrigerator products, and the problem of the filling amount of the refrigerator refrigerant is involved in the design, manufacture and maintenance of the products. In the process of cooling the low-temperature cascade system, if the filling amount of a low-temperature-level refrigerant is too large, the exhaust temperature of a compressor is too high, the power consumption is increased, and the most serious influence is that the low-temperature-level evaporation pressure is higher, and the system cannot reach the expected temperature; if the low-temperature refrigerant is too small in charging amount, the flow of the refrigerant in the system is too small, the cooling speed is slow, and the expected temperature cannot be reached. Because the low-temperature refrigerator is usually placed indoors, the fluctuation of the ambient temperature is not large, the low-temperature refrigerator only needs to be started and stopped within a specified temperature range in the stable working process, and the establishment process of the low-temperature environment is not frequently repeated under special conditions. The problem of accurately calculating the refrigerant charge amount has not been solved well so far, and in order to ensure that the target temperature is reached in the existing ultra-low temperature refrigerator, the charge amount is generally small, the cooling speed is generally slow, and although the charge amount is increased, the rapid cooling can be realized, but the target low temperature environment is difficult to obtain due to the limit of the evaporation pressure. An empirical estimation method (multiplying different coefficients by the volumes of containers of a refrigerator system) is commonly adopted in laboratories and engineering to fill refrigerants in a cascade refrigeration system, and a calculation result often has certain deviation, so that a low-temperature refrigerator cannot efficiently reach a specified cooling target.
Disclosure of Invention
The invention aims to provide a refrigerant charge self-adjusting mechanism and a control method thereof in the cooling process of a low-temperature refrigerator, and provides a solution for the problems that the refrigerant charge calculation error of the ultra-low-temperature refrigerator is large, the automatic adjustment of a refrigerating system is poor, the working condition of the system is continuously changed in the cooling process, the refrigerant charge is improper, the cooling time of the refrigerating system is long, and even the set low-temperature environment cannot be obtained.
In order to achieve the purpose, the invention adopts the following technical scheme:
the self-adaptive filling amount adjusting system for the cooling process of the ultra-low temperature refrigerator comprises a low-temperature refrigeration subsystem and a high-temperature refrigeration subsystem, wherein the two refrigeration subsystems are connected through a condensation evaporator;
in the low-temperature stage refrigeration subsystem, an outlet of an evaporator in the box body is connected with an inlet of a capillary pipeline of the expansion tank and an inlet of a first channel of the heat regenerator, and an outlet of the first channel of the heat regenerator is connected with an inlet of the evaporator in the box body through a low-temperature stage compressor, a second channel of the heat regenerator, a first channel of the condensing evaporator and a low-temperature stage throttling capillary tube which are sequentially connected; the outlet of the expansion tank capillary pipeline is connected with a safe expansion tank; two stop valve-expansion tank structures are arranged on a pipeline between the outlet of the second channel of the condensing evaporator and the inlet of the low-temperature stage throttling capillary tube;
in the high-temperature-stage refrigeration subsystem, the outlet of the high-temperature-stage compressor is sequentially connected with the condenser, the high-temperature-stage throttling capillary tube, the second channel of the condensing evaporator and the inlet of the high-temperature-stage compressor.
Furthermore, the two stop valve-expansion tank structures comprise a first-stage expansion tank and a second-stage expansion tank, and the outlets of the first-stage expansion tank and the second-stage expansion tank are respectively provided with a first-stage stop valve and a second-stage stop valve.
Furthermore, the peripheries of the first-stage expansion tank and the second-stage expansion tank are respectively provided with first-stage electric heating and second-stage electric heating.
Further, the primary expansion tank and the secondary expansion tank have the same structure; the double-stage expansion tank adopts an air bag type expansion tank structure and comprises a tank body, an air bag and an air transmission port; the air bag is arranged in the tank body, the air transmission port is connected with the air bag, and the refrigerant enters the air bag through the air transmission port; and nitrogen is filled between the air bag and the tank body, when the pressure in the refrigeration system rises, the refrigeration working medium is extruded into the air bag to expand the air bag, the nitrogen in the tank body is compressed, and the nitrogen pressure rises until the system pressure and the nitrogen pressure reach balance.
Further, the first-level expansion tank and the second-level expansion tank adopt air bag type expansion tank structures, and the volume design formula of the expansion tanks is as follows:
Figure BDA0002374997720000031
wherein: vtank-expansion tank volume;
alpha-low temperature refrigerant volume expansion coefficient;
delta T is the reduction degree of the heat exchange temperature difference in the condensation evaporator after one expansion tank is opened; the delta T for opening the primary expansion tank is 5-6 ℃; the secondary expansion tank takes values according to the heat exchange temperature difference of the maximum condensation evaporator which a user wants to adjust;
Vtot-total volume of the low temperature stage refrigeration subsystem;
x-at design cryogenic refrigeration System condensation temperature TeHAnd on the basis of designing the refrigerating capacity of the high-temperature refrigerating system, TeHThe dryness of the low-temperature refrigerant at the outlet of the condensing evaporator is higher than the saturation pressure corresponding to the + delta T;
m is the theoretical charge of the low-temperature stage refrigeration subsystem;
rho is the density value of the low temperature refrigerant at 0 ℃ under the preset pressure of the safe expansion tank.
Furthermore, a condensing fan is arranged on the outer side of the condenser in a facing manner.
Furthermore, in the process of cooling the low-temperature refrigerator, the heat exchange temperature difference at the condensing evaporator is an important sign for judging whether the filling amount of the system refrigerant reaches the optimal matching state; t is0Indicating a target temperature, T, set by the usercLDenotes the low-temperature stage condensation temperature, PcLDenotes the low-temperature stage condensation pressure,. DELTA.TLIndicating the degree of subcooling, T, of the refrigerant at the low temperature stageeHIndicating the high-temperature stage evaporation temperature, Δ THIndicating the degree of superheat, T, of the high-temperature-stage refrigerant1Indicates the temperature in the box at the present time, T2Is shown at T1On the basis, the temperature in the box is 30min after the system normally operates; the control method in the cooling process comprises the following steps:
user-set target temperature T0Thereafter, the system starts to operate, at which timeThe first-stage stop valve and the second-stage stop valve of the two stop valve-expansion tank structures are both in a closed state, the electric heating device does not work, and the temperature in the refrigerator continuously drops; when the system detects that the temperature is within 30min, the temperature in the refrigerator is reduced by T1-T2≤0.025(-T0) Time, system to low temperature stage condensation temperature TcLSupercooling degree delta T of low-temperature refrigerantLHigh-temperature stage evaporation temperature TeHHigh-temperature refrigerant superheat degree delta THDetecting if (T)cL-TeH)-0.5ΔTL+0.082ΔTHThe temperature is less than or equal to 5 ℃, and the system sends out an alarm prompt of 'insufficient filling of system refrigerant'; if (T)cL-TeH)-0.5ΔTL+0.082ΔTHThe temperature is more than or equal to 10 ℃, the first-stage stop valve and the second-stage stop valve of the system are opened simultaneously and closed simultaneously after 10s, and the pressure is PcLThe gas-liquid two-phase low-temperature refrigerant enters a first-stage expansion tank and a second-stage expansion tank, the circulating amount of the refrigerant in the low-temperature subsystem is reduced, the system continues to operate stably, if the slow cooling is detected, and the temperature is reduced (T)cL-TeH)-0.5ΔTL+0.082ΔTHIf the temperature is more than or equal to 5 ℃, the excessive filling degree of the system refrigerant is more than the adjusting range, manual adjustment is needed, and the system sends out an alarm prompt of 'excessive filling of the system refrigerant'; if 5 ℃ < (T)cL-TeH)-0.5ΔTL+0.082ΔTHIf the temperature is less than 10 ℃, the condition that the low-temperature-level refrigerant is light and overcharged is shown, the first-level stop valve of the system is closed after being opened for 10s, and the light weight of the refrigerant in the low-temperature-level subsystem is reduced; after the expansion tank opening task is executed, if the temperature rise condition in the refrigerator shows that the circulation volume of the refrigerant is reduced too much, at the moment, if the system only starts the first-stage expansion tank when the heat exchange temperature difference of the condensation evaporator is monitored for the first time, the first-stage stop valve is opened at the moment, the electric heating is started, and the system is closed after 2 min; if the system starts the two-stage expansion tank when monitoring the heat exchange temperature difference of the condensing evaporator for the first time, simultaneously starting the first-stage stop valve and the second-stage stop valve, starting electric heating, and closing after 2 min; through the automatic adjustment, if the system still does not reach the target temperature, the temperature difference of the heat exchange in the condensation evaporator is small, the supercooling degree of the low-temperature-level sub-refrigeration system is large, and the superheat degree of the high-temperature-level sub-refrigeration system is highSmall in size: (T)cL-TeH)-0.5ΔTL+0.082ΔTHAnd (5) judging the device to be in other faults.
Further, after a user initiates a shutdown instruction, firstly, the low-temperature compressor and the high-temperature compressor are respectively closed, the condensing fan is closed, then, in order to ensure that the double-stage expansion tank-stop valve mechanism is restored to the initial state before operation, the first-stage stop valve and the second-stage stop valve are opened, the first-stage electric heating and the second-stage electric heating are started, the electric heating is firstly closed after 10min, and then, the stop valves are closed.
Compared with the prior art, the invention has the following beneficial effects:
the double-stage stop valve-expansion tank structure can automatically adjust the refrigerant circulation volume of the low-temperature refrigeration subsystem in the cooling process of the low-temperature refrigerator in a conventional range, the device can accurately adjust the refrigerant circulation volume in the low-temperature subsystem in the cooling process by monitoring the cooling speed, the heat exchange temperature difference at the condensation evaporator, the supercooling degree of the low-temperature subsystem and the superheat degree of the high-temperature subsystem, the refrigerant circulation volume can be increased in the early stage of cooling, the evaporation pressure is effectively reduced to a reasonable range in the later stage of cooling, the cooling speed of the system is greatly increased, and the common problems of the low-temperature refrigerator in a low-temperature environment, such as inaccurate calculation of theoretical refrigerants or over-high evaporation pressure caused by inaccurate filling process, can.
Under the special condition that the charging quantity exceeds the control range or cannot reach the target temperature due to the reason of non-charging quantity, the device can send out an alarm signal, so that the problem of the refrigeration system can be solved conveniently and efficiently.
And after the low-temperature refrigerator sends a shutdown instruction, the low-temperature stage compressor, the high-temperature stage compressor and the condensing fan are respectively closed, the two stop valves are simultaneously opened and the electric heating device is started, the electric heating device is closed after 10min, the stop valves are closed, and the shutdown process is finished. The electric heating device can enable refrigerant in the expansion tank to enter the system to the maximum extent, so that the expansion tank is restored to the original state, and the normal use of the expansion tank in the next cooling process is ensured.
The double-stage stop valve-expansion tank structure has low cost and small and compact structure, and is suitable for a low-temperature refrigerator refrigerating system with compact structure.
Adopt gasbag formula expansion tank structure, prevent effectively that nitrogen gas from getting into refrigerating system and influencing refrigeration effect. The invention provides an expansion tank volume design formula when a refrigerant is in a two-phase state, and the volume of a two-stage expansion tank is designed and calculated through the formula, so that a low-temperature stage refrigeration subsystem can reduce a certain condensation pressure by opening the expansion tank when the refrigerant filling amount is overlarge, and further reduce a certain condensation temperature.
Drawings
FIG. 1 is a schematic diagram of a self-adaptive control system for the filling amount in the cooling process of an ultra-low temperature refrigerator adopting a double-stage expansion tank-stop valve mechanism;
FIG. 2 is a block diagram of the expansion tank of the present invention;
FIG. 3 is a flow chart of a refrigerant circulation self-regulation control method of the present invention;
FIG. 4 is a flow chart of the expansion tank-stop valve mechanism resetting of the invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Under the condition of small refrigerant filling amount, the refrigerant circulation amount in the low-temperature system is small, the refrigerating capacity is small, the system is slowly cooled, but the refrigerant circulation amount of the low-temperature subsystem is small, the heat exchange area of the condensing evaporator is enough, and the heat exchange temperature difference of the condensing evaporator is small; when the refrigerant filling amount is large, the refrigerant circulation amount in the low-temperature-level subsystem is large, the refrigerating capacity is large, the early-stage cooling speed of the system is high, but the temperature is reduced to about 85% of the target temperature, the system is cooled very slowly, the main reason is that the system pressure is increased due to the fact that the refrigerant filling amount is too large, the cold energy generated by the high-temperature-level subsystem in the condensation evaporator is not enough to condense the low-temperature-level refrigerant to a saturated liquid state, the low-temperature-level subsystem basically has no supercooling degree, the superheat degree of the high-temperature-level subsystem is too large, the heat exchange effect in the condensation evaporator is poor, the heat exchange temperature difference is large, the condensation pressure of the low-temperature-level subsystem is further increased, the comprehensive effect of the system is too high, the evaporation temperature; when the charging amount of the system is in a reasonable range, the cooling speed of the system is still higher after the temperature is reduced to 80% of the target temperature, and at the moment, the heat exchange temperature difference at the condensing evaporator reaches a reasonable range of about 5 ℃, the low-temperature subsystem has a certain supercooling degree, and the superheat degree of the high-temperature subsystem is also in a reasonable range. In conclusion, under the condition that the components of the refrigeration system of the low-temperature refrigerator are reasonably designed, the cooling speed of the system, the heat exchange temperature difference at the condensing evaporator, the supercooling degree of the low-temperature subsystem and the superheat degree of the high-temperature subsystem are main criteria for judging whether the charge quantity is proper or not.
In the cooling process of the cascade ultralow temperature refrigerator, along with the continuous reduction of the temperature in the refrigerator, the working condition of a refrigeration system is continuously changed, if the target temperature is efficiently reached, the circulation amount of a low-temperature refrigerant needs to be properly increased in the early stage of cooling, the refrigeration amount of the system is increased, and the cooling speed is greatly increased; and in the later stage of temperature reduction, the refrigerant is properly reduced, and lower evaporation pressure is obtained, so that the target low-temperature environment is ensured to be obtained smoothly.
A double-stage stop valve-expansion tank mechanism is added between the traditional cascade circulation low-temperature stage capillary tube and the condensing evaporator. An electric heating device is arranged outside the expansion tank. Through monitoring the cooling speed of the low-temperature refrigerator and the opening and closing of the heat exchange temperature difference control stop valve and the electric heating device at the condensation evaporator of the system, the refrigerant filling amount in the low-temperature refrigeration subsystem is automatically adjusted within a certain range, and when the refrigerant filling amount exceeds the adjusting range or causes the problem of slow cooling due to the non-filling amount, the system can send corresponding signals, so that the refrigeration system can be further adjusted manually. The device can effectively reduce the cooling time of the low-temperature refrigerator, improve the system operation efficiency and improve the fault maintenance efficiency.
Referring to fig. 1, the present invention provides a self-adaptive charge control system for cooling process of ultra-low temperature refrigerator, which comprises a low temperature stage refrigeration subsystem and a high temperature stage refrigeration subsystem, wherein the two refrigeration subsystems are connected by a condensing evaporator 4.
The low-temperature stage refrigeration subsystem comprises an evaporator 1 in a box body, a low-temperature stage compressor 2, a heat regenerator 3, a first-stage stop valve 5, a first-stage expansion tank 6, a second-stage stop valve 7, a second-stage expansion tank 8, a low-temperature stage throttling capillary tube 9, an expansion tank capillary tube 14, a safe expansion tank 15, a first-stage electric heater 16 and a second-stage electric heater 17.
The outlet of the evaporator 1 in the box body is connected with the inlet of the expansion tank capillary pipeline 14 and the inlet of the first channel of the heat regenerator 3, and the outlet of the first channel of the heat regenerator 3 is connected with the inlet of the evaporator 1 in the box body through the low-temperature stage compressor 2, the second channel of the heat regenerator 3, the first channel of the condensing evaporator 4 and the low-temperature stage throttling capillary tube 9 which are connected in sequence. The outlet of the expansion tank capillary line 14 is connected to a safety expansion tank 15. The pipeline between the second channel outlet of the condensing evaporator 4 and the inlet of the low-temperature stage throttling capillary tube 9 is communicated with a first-stage expansion tank 6 and a second-stage expansion tank 8, and the outlets of the first-stage expansion tank 6 and the second-stage expansion tank 8 are respectively provided with a first-stage stop valve 5 and a second-stage stop valve 7. The peripheries of the first-stage expansion tank 6 and the second-stage expansion tank 8 are respectively provided with a first-stage electric heater 16 and a second-stage electric heater 17.
The high temperature stage refrigeration subsystem includes a high temperature stage compressor 10, a condenser 11, a condensing fan 12, and a high temperature stage throttling capillary tube 13. The outlet of the high-temperature stage compressor 10 is sequentially connected with the condenser 11, the high-temperature stage throttling capillary tube 13, the second channel of the condensing evaporator 4 and the inlet of the high-temperature stage compressor 10. The outside of the condenser 11 is provided with a condensing fan 12.
Two stop valve-expansion tank structures are arranged between the condensing evaporator 4 and the low-temperature stage throttling capillary tube 9, and the primary stop valve 5 and the secondary stop valve 7 respectively control the connection and disconnection of the primary expansion tank 6 and the secondary expansion tank 8 with the system; the expansion tank outside is equipped with electric heater unit, and its effect has two: when the low-temperature-level refrigerant is insufficient, the refrigerant liquid in the expansion tank is heated, so that the pressure of the refrigerant in the tank is increased, and a refrigerating system is supplemented; and secondly, after the system is shut down, the stop valve is opened and the electric heating is started, and after 10min, the stop valve and the electric heating are closed, so that the expansion tank is kept in a low-pressure state as far as possible to ensure the self-regulating function of the refrigerant charging amount in the next cooling process.
Fig. 2 is a schematic diagram showing the structures of the primary expansion tank 6 and the secondary expansion tank 7. The double-pole expansion tank adopts an air bag type expansion tank structure, and comprises a tank body 18, an air bag 19 and an air transmission port 20. The air bag 19 is placed in the tank 18, the gas transmission port 20 is connected to the air bag 19, and the refrigerant is introduced into the air bag through the gas transmission port 20. And nitrogen is filled between the air bag and the tank body, when the pressure in the refrigeration system rises, the refrigeration working medium is extruded into the air bag to expand the air bag, the nitrogen in the tank body is compressed, and the nitrogen pressure rises until the system pressure and the nitrogen pressure reach balance. The expansion tank structure can effectively prevent nitrogen from leaking into the refrigeration system and influencing the normal operation of the refrigeration system.
One-level expansion tank, second grade expansion tank adopt gasbag formula expansion tank structure, and the volume design formula of expansion tank is as follows:
Figure BDA0002374997720000091
wherein: vtank-expansion tank volume;
alpha-low temperature refrigerant volume expansion coefficient;
delta T is the reduction degree of the heat exchange temperature difference in the condensation evaporator after one expansion tank is opened; the delta T for opening the primary expansion tank is 5-6 ℃; the secondary expansion tank takes values according to the heat exchange temperature difference of the maximum condensation evaporator which a user wants to adjust;
Vtot-total volume of the low temperature stage refrigeration subsystem;
x-at design cryogenic refrigeration System condensation temperature TeHAnd on the basis of designing the refrigerating capacity of the high-temperature refrigerating system, TeHThe dryness of the low-temperature refrigerant at the outlet of the condensing evaporator is higher than the saturation pressure corresponding to the + delta T;
m is the theoretical charge of the low-temperature stage refrigeration subsystem;
rho is the density value of the low temperature refrigerant at 0 ℃ under the preset pressure of the safe expansion tank.
In order to make the improved two-stage expansion tank-stop valve cascade refrigeration cycle system operate efficiently and stably under a set working condition and achieve an ideal function, the control of the operation stage and the shutdown stage of the cooling process is explained as follows:
as shown in FIG. 3, with T0Indicating a target temperature, T, set by the usercLIndicating low temperature stage condensationTemperature, Δ TLIndicating the degree of subcooling, T, of the refrigerant at the low temperature stageeHIndicating the high-temperature stage evaporation temperature, Δ THIndicating the degree of superheat, T, of the high-temperature-stage refrigerant1Indicates the temperature in the box at the present time, T2Is shown at T1And on the basis, the temperature in the box is 30min after the system normally operates.
User-set target temperature T0And then, the system starts to work, the first-stage stop valve 5 and the second-stage stop valve 7 are both in a closed state at the moment, the electric heating device does not work, and the temperature in the box continuously drops. When the system detects that the temperature in the box is too slow within 30min, namely T1-T2≤0.025(-T0) Time, system to low temperature stage condensation temperature TcLSupercooling degree delta T of low-temperature refrigerantLHigh-temperature stage evaporation temperature TeHHigh-temperature refrigerant superheat degree delta THDetecting if (T)cL-TeH)-0.5ΔTL+0.082ΔTHThe temperature is less than or equal to 5 ℃, which indicates that under the filling condition, the cold quantity generated by the high-temperature refrigeration subsystem is enough to absorb the condensation heat of the low-temperature refrigeration subsystem, at the moment, the temperature reduction speed is too slow, because the flow of the low-temperature refrigerant is too small, the evaporation pressure and the condensation pressure of the low-temperature refrigeration subsystem are both lower than normal levels, the refrigerant filling of the low-temperature refrigeration subsystem is carried out in time, and the device sends out the alarm prompt of 'insufficient filling of the system refrigerant'; if (T)cL-TeH)-0.5ΔTL+0.082ΔTHNot less than 10 ℃, which indicates that the heat exchange effect of the refrigerant on two sides in the condensation evaporator is poor at the moment, the low-temperature-level refrigerant is still in a gas-liquid two-phase state at the outlet of the condensation evaporator, the dryness is high, the low-temperature-level evaporation pressure is high, the target low-temperature environment cannot be obtained, the low-temperature-level refrigerant is excessively filled, the first-level stop valve and the second-level stop valve of the system are opened at the same time, the system is closed at the same time after 10scLThe gas-liquid two-phase low-temperature refrigerant enters the first-stage expansion tank and the second-stage expansion tank, the refrigerant circulation amount in the low-temperature subsystem is reduced, the system continues to run stably, if the temperature reduction is detected slowly, and the heat exchange temperature difference in the condensation evaporator is large, the excessive degree of the refrigerant filling of the system is over the adjusting range, manual adjustment is needed, and the deviceIssuing a warning of "system refrigerant overfill"; if 5 ℃ < (T)cL-TeH)-0.5ΔTL+0.082ΔTHThe temperature is less than 10 ℃, which indicates that the heat exchange effect of the high-temperature-level refrigerant and the low-temperature-level refrigerant in the condensation evaporator 4 is poor, the low-temperature-level refrigerant is still a gas-liquid two-phase mixture which is not cooled to a saturated liquid state at the outlet of the condensation evaporator, the low-temperature-level refrigerant has a light-weight overcharge condition, the low-temperature-level charge amount is adjusted, the first-level stop valve of the system is opened for 10s and then closed, and the pressure is PcLThe gas-liquid two-phase low-temperature-level refrigerant enters the first-level expansion tank, the refrigerant in the low-temperature-level subsystem is reduced in light weight, the system continues to operate stably, and the temperature in the tank continues to be monitored.
After the expansion tank opening task is executed, if the temperature rise condition in the tank indicates that the circulation volume of the refrigerant is reduced too much, at the moment, if the system only starts the first-stage expansion tank when the heat exchange temperature difference of the condensation evaporator is monitored for the first time, the first-stage stop valve is opened at the moment, the electric heating is started, and the system is closed after 2 min; if the system starts the two-stage expansion tank when monitoring the heat exchange temperature difference of the condensation evaporator for the first time, the first-stage stop valve and the second-stage stop valve are opened simultaneously, the electric heating is started, and the system is closed after 2 min. After the adjustment of the filling amount, the system runs stably for a period of time, and the low-temperature level condensation pressure PcLAnd when the pressure in the expansion tank is slightly lower than the pressure in the expansion tank at the moment, the stop valve is opened to supplement part of the refrigerant into the system, but the supplement capacity is limited, the pressure in the expansion tank can be further increased by starting the electric heating for 2min, but only the part of the refrigerant in the tank can be supplemented into the refrigeration system due to short heating time, and the stop valve is closed at the moment to enable the system to continue to normally operate.
By the above automatic adjustment, if the system has not reached the target temperature, but (T)cL-TeH)-0.5ΔTL+0.082ΔTHAnd the temperature is less than or equal to 5 ℃, and the device judges that other faults occur in the system, so that the system can be conveniently checked manually, and other problems except improper refrigerant filling amount can be solved.
The system shutdown process flow chart is as shown in fig. 4, after a shutdown instruction is initiated by a user, the low-temperature stage compressor and the high-temperature stage compressor are respectively closed, the condensing fan is closed, then the first-stage stop valve and the second-stage stop valve are opened to ensure that the double-stage expansion tank-stop valve mechanism is restored to the initial state before operation, the first-stage electric heating and the second-stage electric heating are started, the electric heating is closed after 10min, and then the stop valves are closed. When the system is just shut down, the temperature in the system is low, the pressure in the low-temperature stage refrigeration subsystem is low, the low-temperature refrigerant belongs to a high-pressure refrigerant, when the electric heating is started to heat the refrigerant in the tank, the pressure rise range of the refrigerant in the tank is large, so that the pressure difference between the inside and the outside of the tank is more obvious, the refrigerant in the tank can enter the refrigeration system to the maximum extent, and the cyclic use of the two-stage expansion tank-stop valve mechanism is ensured.
The improved cascade type low-temperature refrigerator refrigerating system can ensure the cooling speed of the system in the early stage of the cooling process, and accurately reduce the evaporation temperature of the system through the opening and closing of the two-stage stop valve-expansion tank mechanism in the later stage of cooling, thereby realizing the rapid and strengthened cooling effect; moreover, the mechanism can automatically adjust the refrigerant circulation volume of the system under the condition of excessive refrigerant filling, and ensure that the cooling process reaches the standard efficiently. In addition, whether modified cascade low temperature refrigerator refrigerating system accessible monitoring system cooling speed, condensation evaporator heat transfer difference in temperature, low temperature level subsystem subcooling degree and high temperature level subsystem superheat degree fill the refrigerant in right amount and judge, fill the refrigerant and fill and exceed control range or fill the problem because of non-refrigerant and lead to the system cooling too slow and send corresponding alarm, be convenient for the manual work to further adjust refrigerating system, the high-efficient problem of solving.
It will be appreciated by those skilled in the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed above are therefore to be considered in all respects as illustrative and not restrictive. All changes which come within the scope of or equivalence to the invention are intended to be embraced therein.

Claims (7)

1. The self-adaptive filling amount adjusting system for the cooling process of the ultra-low temperature refrigerator is characterized by comprising a low-temperature refrigeration subsystem and a high-temperature refrigeration subsystem, wherein the two refrigeration subsystems are connected through a condensation evaporator (4);
in the low-temperature stage refrigeration subsystem, an outlet of an evaporator (1) in a box body is connected with an inlet of an expansion tank capillary pipeline (14) and an inlet of a first channel of a heat regenerator (3), and an outlet of the first channel of the heat regenerator (3) is connected with an inlet of the evaporator (1) in the box body through a low-temperature stage compressor (2), a second channel of the heat regenerator (3), a first channel of a condensing evaporator (4) and a low-temperature stage throttling capillary tube (9) which are connected in sequence; the outlet of the expansion tank capillary pipeline (14) is connected with a safe expansion tank (15); two stop valve-expansion tank structures are arranged on a pipeline between the outlet of the first channel of the condensing evaporator (4) and the inlet of the low-temperature throttling capillary tube (9);
in the high-temperature-stage refrigeration subsystem, the outlet of a high-temperature-stage compressor (10) is sequentially connected with a condenser (11), a high-temperature-stage throttling capillary tube (13), a second channel of a condensing evaporator (4) and the inlet of the high-temperature-stage compressor (10).
2. The self-adaptive adjusting system for the filling amount in the cooling process of the ultra-low temperature refrigerator as claimed in claim 1, wherein the two stop valve-expansion tank structures comprise a primary expansion tank (6) and a secondary expansion tank (8), and the primary stop valve (5) and the secondary stop valve (7) are respectively arranged at the outlets of the primary expansion tank (6) and the secondary expansion tank (8).
3. The self-adaptive charge control system for the cooling process of the ultra-low temperature refrigerator as claimed in claim 2, wherein the primary electric heater (16) and the secondary electric heater (17) are respectively arranged on the peripheries of the primary expansion tank (6) and the secondary expansion tank (8).
4. The self-adaptive adjusting system for the filling amount in the cooling process of the ultra-low temperature refrigerator as claimed in claim 2, wherein the primary expansion tank (6) and the secondary expansion tank (8) have the same structure; the double-stage expansion tank adopts an air bag type expansion tank structure and comprises a tank body (18), an air bag (19) and an air transmission port (20); the air bag (19) is arranged in the tank body (18), the air transmission port (20) is connected with the air bag (19), and the refrigerant enters the air bag through the air transmission port (20); and nitrogen is filled between the air bag and the tank body, when the pressure in the refrigeration system rises, the refrigeration working medium is extruded into the air bag to expand the air bag, the nitrogen in the tank body is compressed, and the nitrogen pressure rises until the system pressure and the nitrogen pressure reach balance.
5. The self-adaptive adjusting system for the filling amount in the cooling process of the ultra-low temperature refrigerator as claimed in claim 4, wherein the primary expansion tank (6) and the secondary expansion tank (8) adopt an air bag type expansion tank structure, and the volume design formula of the expansion tanks is as follows:
Figure FDA0002663216570000021
wherein: vtank-expansion tank volume;
alpha-low temperature refrigerant volume expansion coefficient;
delta T is the reduction degree of the heat exchange temperature difference in the condensation evaporator after one expansion tank is opened; the delta T for opening the primary expansion tank is 5-6 ℃; the secondary expansion tank takes values according to the heat exchange temperature difference of the maximum condensation evaporator which a user wants to adjust;
Vtot-total volume of the low temperature stage refrigeration subsystem;
x-at design cryogenic refrigeration System condensation temperature TeHAnd on the basis of designing the refrigerating capacity of the high-temperature refrigerating system, TeHThe dryness of the low-temperature refrigerant at the outlet of the condensing evaporator (4) is higher than the saturation pressure corresponding to + delta T;
m is the theoretical charge of the low-temperature stage refrigeration subsystem;
rho-the density value of the cryogenic refrigerant at 0 ℃ at a preset pressure of the safety expansion tank (15).
6. The adaptive control system for the filling amount in the cooling process of the ultra-low temperature refrigerator as claimed in claim 1, wherein a condensing fan (12) is disposed opposite to the outside of the condenser (11).
7. The method for controlling the self-adaptive filling amount adjusting system in the cooling process of the ultra-low temperature refrigerator as claimed in claim 1, wherein: in thatIn the process of cooling the low-temperature refrigerator, the heat exchange temperature difference at the condensing evaporator (4), the supercooling degree of the low-temperature refrigerant at the outlet of the condensing evaporator (4) and the superheat degree of the high-temperature refrigerant at the outlet of the condensing evaporator (4) are signs of whether the filling amount of the system refrigerant reaches the optimal matching state; t is0Indicating a target temperature, T, set by the usercLDenotes the low-temperature stage condensation temperature, PcLDenotes the low-temperature stage condensation pressure,. DELTA.TLIndicating the degree of subcooling, T, of the refrigerant at the low temperature stageeHIndicating the high-temperature stage evaporation temperature, Δ THIndicating the degree of superheat, T, of the high-temperature-stage refrigerant1Indicates the temperature in the box at the present time, T2Is shown at T1On the basis, the temperature in the box is 30min after the system normally operates; the control method in the cooling process comprises the following steps:
user-set target temperature T0Then, the system starts to work, the first-stage stop valve and the second-stage stop valve of the two stop valve-expansion tank structures are both in a closed state, the electric heating device does not work, and the temperature in the refrigerator continuously drops; when the system detects that the temperature is within 30min, the temperature in the refrigerator is reduced by T1-T2≤0.025(-T0) Time, system to low temperature stage condensation temperature TcLSupercooling degree delta T of low-temperature refrigerantLHigh-temperature stage evaporation temperature TeHHigh-temperature refrigerant superheat degree delta THDetecting if (T)cL-TeH)-0.5ΔTL+0.082ΔTHThe temperature is less than or equal to 5 ℃, and the system sends out an alarm prompt of 'insufficient filling of system refrigerant'; if (T)cL-TeH)-0.5ΔTL+0.082ΔTHThe temperature is more than or equal to 10 ℃, the first-stage stop valve and the second-stage stop valve of the system are opened simultaneously and closed simultaneously after 10s, and the pressure is PcLThe gas-liquid two-phase low-temperature refrigerant enters a first-stage expansion tank and a second-stage expansion tank, the circulating amount of the refrigerant in the low-temperature subsystem is reduced, the system continues to operate stably, if the slow cooling is detected, and the temperature is reduced (T)cL-TeH)-0.5ΔTL+0.082ΔTHIf the temperature is more than or equal to 5 ℃, the excessive filling degree of the system refrigerant is more than the adjusting range, manual adjustment is needed, and the system sends out an alarm prompt of 'excessive filling of the system refrigerant'; if 5 ℃ < (T)cL-TeH)-0.5ΔTL+0.082ΔTHIf the temperature is less than 10 ℃, the condition that the low-temperature-level refrigerant is light and overcharged is shown, the first-level stop valve of the system is closed after being opened for 10s, and the light weight of the refrigerant in the low-temperature-level subsystem is reduced; after the expansion tank opening task is executed, if the temperature rise condition in the refrigerator shows that the circulation volume of the refrigerant is reduced too much, at the moment, if the system only starts the first-stage expansion tank when the heat exchange temperature difference of the condensation evaporator is monitored for the first time, the first-stage stop valve is opened at the moment, the electric heating is started, and the system is closed after 2 min; if the system starts the two-stage expansion tank when monitoring the heat exchange temperature difference of the condensing evaporator for the first time, simultaneously starting the first-stage stop valve and the second-stage stop valve, starting electric heating, and closing after 2 min; through above-mentioned automatically regulated, if the system still does not reach the target temperature, and the inside heat transfer difference in temperature of condensation evaporator is less, and low temperature level sub-refrigeration system subcooling degree is on the large side, and high temperature level sub-refrigeration system superheat degree is on the small side: (T)cL-TeH)-0.5ΔTL+0.082ΔTHAnd (5) judging the device to be in other faults.
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