阅读说明：本技术 一种应用于复叠制冷或热泵系统的循环系统及过冷方法 (Circulating system applied to cascade refrigeration or heat pump system and supercooling method ) 是由 杨启超 陈晓楠 迟卫凯 刘利 李连生 赵远扬 刘广彬 于 2021-09-18 设计创作，主要内容包括：本发明属于冷冻冷藏及制冷技术领域,具体涉及一种应用于复叠制冷或热泵系统的循环系统及过冷方法,包括闪蒸罐,闪蒸罐分别连接第二膨胀阀和第三膨胀阀,第二膨胀阀依次连接冷凝蒸发器和高温级压缩机,第三膨胀阀依次连接过冷器和高温级压缩机,高温压缩机依次连接冷凝器、第一膨胀阀后接入闪蒸罐；还包括辅助压缩机,第三膨胀阀依次连接过冷器、辅助压缩机后接入高温级压缩机。本发明在传统复叠制冷系统的基础上,在高温级构建过冷支路,为低温级冷凝器冷凝后的液体提供过冷,从而提高系统性能,提高循环效率,同时,在保证系统性能基础上,简化了系统,提高了安全性。(The invention belongs to the technical field of freezing, refrigeration and refrigeration, and particularly relates to a circulating system and a supercooling method applied to a cascade refrigeration or heat pump system, which comprise a flash tank, wherein the flash tank is respectively connected with a second expansion valve and a third expansion valve, the second expansion valve is sequentially connected with a condensation evaporator and a high-temperature compressor, the third expansion valve is sequentially connected with a subcooler and the high-temperature compressor, and the high-temperature compressor is sequentially connected with a condenser and a first expansion valve and then is connected into the flash tank; the third expansion valve is connected with the subcooler and the auxiliary compressor in sequence and then is connected with the high-temperature compressor. On the basis of the traditional cascade refrigeration system, the invention constructs a supercooling branch at a high-temperature level to provide supercooling for liquid condensed by a low-temperature level condenser, thereby improving the system performance and the cycle efficiency, and simultaneously, on the basis of ensuring the system performance, the invention simplifies the system and improves the safety.)

1. The utility model provides a be applied to cascade refrigeration or heat pump system's circulation system, its characterized in that includes the flash tank, the flash tank connects second expansion valve and third expansion valve respectively, second expansion valve connects gradually condensation evaporator and high temperature stage compressor, the third expansion valve connects gradually subcooler and high temperature stage compressor, the high temperature compressor inserts the flash tank after connecting gradually condenser, first expansion valve.

2. The circulation system of claim 1, further comprising an auxiliary compressor, wherein the flash tank is connected to a second expansion valve and a third expansion valve, respectively, the second expansion valve is connected to the condensing evaporator and the high-temperature stage compressor in sequence, the third expansion valve is connected to the high-temperature stage compressor after being connected to the subcooler and the auxiliary compressor in sequence, and the high-temperature stage compressor is connected to the flash tank after being connected to the condenser and the first expansion valve in sequence.

3. The circulation system of any one of claims 1 or 2, wherein an outlet of the subcooler is connected to the low-temperature stage expansion valve, the evaporator, the low-temperature stage compressor, and the condensing evaporator in sequence, and then connected to an inlet of the subcooler to form a circulation.

4. The circulation system of any one of claims 1 or 2, wherein the outlet of the condenser is connected with a first expansion valve, a flash tank and then connected with a high-temperature stage compressor, and the high-temperature stage compressor is communicated with the condenser.

5. A supercooling method of a circulation system according to any one of claims 1, 3 and 4, wherein a part of refrigerant liquid from the flash tank enters the condensing evaporator to be evaporated into gas after being throttled by the second expansion valve, and a part of refrigerant liquid enters the subcooler through the third expansion valve, and the refrigerant of the heat absorption high temperature level in the subcooler is evaporated into gas; the two paths of refrigerant gas are mixed and then enter a high-temperature stage compressor to be compressed to complete the refrigeration cycle.

6. A supercooling method of a circulation system according to any one of claims 2 to 4, wherein a part of refrigerant liquid from the flash tank is throttled by the second expansion valve, enters the condensing evaporator to be evaporated into gas, and enters the high temperature stage compressor; one path enters the subcooler through the third expansion valve, the high-temperature-stage refrigerant absorbing heat in the subcooler is evaporated into gas, the gas enters the auxiliary compressor, the gas is mixed with the first path after being compressed to the inlet pressure of the high-temperature-stage compressor, and the gas enters the high-temperature-stage compressor for compression, so that the high-temperature-stage refrigeration cycle is completed.

Technical Field

The invention belongs to the technical field of freezing, refrigerating and refrigerating, and particularly relates to a circulating system and a supercooling method applied to a cascade refrigeration or heat pump system.

Background

Supercooling in a cascade refrigeration cycle system in the prior freezing and refrigerating technology has the function of improving and enhancing the system performance, and related theoretical researches are mainly focused on the aspects of a heat regenerator, an air supply system and the like. In recent years, mechanical supercooling has become one of the hot spots in the refrigeration field, but research has been focused mainly on transcritical CO₂Refrigeration and heat pump circulation are mainly arranged in a way that mechanical supercooling circulation is additionally arranged on single-stage refrigeration circulation, and the supercooling circulation effect in a subcritical region and the application potential and performance evaluation work in a cascade refrigeration system are less. The mechanical supercooling method is that a subcooler is arranged at the outlet of a condenser, and the cold energy of the subcooler is provided by a single refrigeration cycle, such as a conventional vapor compression refrigeration system, an absorption refrigeration system or a thermoelectric refrigeration system, and the like, so that additional components are added, the system is relatively complex, and the leakage of a refrigerant is easily caused, thereby causing safety accidents.

The supercooling technology is one of effective measures for improving the performance of a refrigerating system and a circulating system thereof, and can be realized by arranging a subcooler, a plate economizer, mechanical supercooling level thermoelectric supercooling and the like. The arrangement of the subcooler is realized by increasing the heat exchange area of the condenser on the basis of the condenser, the subcooling effect of the subcooler is influenced by the temperature of a cooling water inlet and is limited by the evaporation temperature of a high-temperature level in a cascade refrigeration system, the refrigerant of the low-temperature level cannot be subcooled to be lower than the evaporation temperature of the high-temperature level through the evaporation condenser, and a heat exchange temperature difference exists in a condensation evaporator, namely the evaporation temperature of the high-temperature level is lower than the condensation temperature of the low-temperature level, so that the subcooling effect is limited.

Disclosure of Invention

The invention aims to solve the problems in the prior art, and provides a circulating system and a supercooling method applied to a cascade refrigeration or heat pump system.

The technical scheme of the invention is as follows:

the utility model provides a be applied to cascade refrigeration or heat pump system's circulation system, includes the flash tank, second expansion valve and third expansion valve are connected respectively to the flash tank, second expansion valve connects gradually condensation evaporator and high temperature stage compressor, third expansion valve connects gradually subcooler and high temperature stage compressor, the high temperature compressor inserts the flash tank after connecting gradually condenser, first expansion valve.

The utility model provides a be applied to cascade refrigeration or heat pump system's circulation system, still includes auxiliary compressor, second expansion valve and third expansion valve are connected respectively to the flash tank, second expansion valve connects gradually condensation evaporator and high-temperature compressor, the third expansion valve inserts high-temperature compressor behind connecting gradually subcooler, the auxiliary compressor, the high-temperature compressor inserts the flash tank behind connecting gradually condenser, first expansion valve.

Furthermore, one outlet of the subcooler is sequentially connected with the low-temperature stage expansion valve, the evaporator, the low-temperature stage compressor and the condensation evaporator, and then is connected into one inlet of the subcooler to form circulation.

Further, the outlet of the condenser is sequentially connected with the first expansion valve and the flash tank and then connected with the high-temperature stage compressor, and the high-temperature stage compressor is communicated with the condenser.

A supercooling method applied to a circulation system of a cascade refrigeration or heat pump system includes two circulation schemes, wherein,

the first scheme is as follows: one path of refrigerant liquid from the flash tank is throttled by a second expansion valve and enters a condensation evaporator to be evaporated into gas, and then enters a high-temperature stage compressor; one path enters the subcooler through the third expansion valve, the high-temperature-stage refrigerant absorbing heat in the subcooler is evaporated into gas, the gas enters the auxiliary compressor, the gas is mixed with the first path after being compressed to the inlet pressure of the high-temperature-stage compressor, and the gas enters the high-temperature-stage compressor for compression, so that the high-temperature-stage refrigeration cycle is completed. (corresponding to FIG. 1)

The second scheme is as follows: one path of refrigerant liquid from the flash tank enters a condensing evaporator after being throttled by a second expansion valve and is evaporated into gas, and the other path of refrigerant liquid enters a subcooler through a third expansion valve and absorbs heat in the subcooler and is evaporated into gas at a high-temperature level; the two paths of refrigerant gas are mixed and then enter a high-temperature stage compressor to be compressed to complete the refrigeration cycle. (corresponding to FIG. 2)

The invention has the beneficial effects that:

the circulating system and the supercooling method provided by the invention comprise two schemes, firstly, on the basis of high-temperature refrigeration circulation, a new loop is arranged, a 2 nd expansion valve, a subcooler and an auxiliary compressor are added to realize supercooling of a low-temperature refrigerant, deep throttling is carried out by using the high-temperature refrigerant with less flow to realize supercooling of a low-temperature level, the unit refrigerating capacity of the low-temperature level refrigerant is improved, and the performance coefficient of the whole cascade system is improved; and secondly, the total power consumption of the system is reduced by increasing the supercooling degree of the low-temperature level and increasing the refrigerating capacity of the low-temperature level refrigerant per unit mass, the COP of the system is improved, meanwhile, an auxiliary compressor on a supercooling branch is omitted on the basis of the scheme 1, a condenser and a compressor are omitted compared with mechanical supercooling overlapping, the system is simplified on the basis of ensuring the performance of the system, and the safety is improved. In addition, the supercooling method provided by the invention can also effectively reduce the exhaust pressure of the high-temperature stage compressor and improve the condition that the exhaust temperature of the high-temperature stage compressor is overhigh.

Drawings

FIG. 1 is a schematic diagram of a low temperature stage subcooling cascade refrigeration cycle scheme according to the present invention;

FIG. 2 is a schematic diagram of a second embodiment of the low temperature stage subcooling cascade refrigeration cycle according to the present invention;

FIG. 3 is a schematic diagram of a mechanical subcooling cascade refrigeration cycle;

FIG. 4 is a pressure-enthalpy diagram of a low-temperature stage subcooling cascade refrigeration cycle;

in each of the above figures, 1, a low-temperature stage compressor; 2. a condensing evaporator; 3. a subcooler; 4. a low-temperature stage expansion valve; 5. an evaporator; 6. a high temperature stage compressor; 7. a condenser; 8. a first expansion valve; 9. a flash tank; 10. a second expansion valve; 11. a third expansion valve; 12. an auxiliary compressor; 13. a high-temperature stage expansion valve; 14. a mechanical super-cooling compressor; 15. a mechanical subcooling condenser; 16. a mechanical subcooling expansion valve.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

For a further understanding of the invention, reference will now be made to the following description taken in conjunction with the accompanying drawings and examples.

Example 1

As shown in fig. 1, the circulation system applied to the cascade refrigeration or heat pump system according to this embodiment includes a flash tank 9 and an auxiliary compressor 12, the flash tank 9 is respectively connected to a second expansion valve 10 and a third expansion valve 11, the second expansion valve 10 is sequentially connected to a condensation evaporator 2 and a high-temperature stage compressor 6, the third expansion valve 11 is sequentially connected to a subcooler 3 and the auxiliary compressor 12 and then connected to the high-temperature stage compressor 6, and the high-temperature compressor is sequentially connected to a condenser 7 and a first expansion valve 8 and then connected to the flash tank 9.

In addition, the circulating system also comprises two paths, namely, one path of outlet of the subcooler 3 is sequentially connected with the low-temperature stage expansion valve 4, the evaporator 5, the low-temperature stage compressor 1 and the condensing evaporator 2, and then is connected into one path of inlet of the subcooler 3 to form circulation. An outlet of the condenser 7 is sequentially connected with a first expansion valve 8 and a flash tank 9 and then connected with a high-temperature stage compressor 6, and the high-temperature stage compressor 6 is communicated with the condenser 7.

The conventional cascade refrigeration system consists of two refrigeration systems, namely a low-temperature stage refrigeration cycle consisting of a low-temperature stage compressor 1, a condensation evaporator 2, a low-temperature stage expansion valve 4 and an evaporator 5 and a high-temperature stage refrigeration cycle consisting of a high-temperature stage compressor 6, a condenser 7, a first expansion valve 8, a flash tank 9, a second expansion valve 10 and a condensation evaporator 2. On the basis, the embodiment provides a method for providing supercooling through a high-temperature stage cycle, so as to cool the refrigerant liquid coming out of the condensation evaporator 2 in the low-temperature stage cycle, improve the supercooling degree, improve the refrigerating capacity of the unit refrigerant flow of the low-temperature stage cycle and improve the total coefficient of performance (COP) of the system.

The supercooling method of the circulating system is that one path of refrigerant liquid from the flash tank 9 enters the condensation evaporator 2 after being throttled by the second expansion valve 10 and is evaporated into gas, and then enters the high-temperature stage compressor 6. And the other path of the refrigerant enters the subcooler 3 through the third expansion valve 11, is evaporated into gas to enter the auxiliary compressor 12, is compressed to the inlet pressure of the high-temperature stage compressor 6, is mixed with the other path of the gas, and then enters the high-temperature stage compressor 6 for compression.

The low-temperature-level refrigerant which is circulated out of the condensing evaporator 2 in the low-temperature level is further cooled by the arrangement of the subcooler 3, namely, the subcooling degree of the low-temperature-level circulation is improved, and the system performance is improved. The pressure after passing through the third expansion valve 11 is lower than the pressure after passing through the second expansion valve 10, that is, for the high-temperature stage cycle, the evaporation temperature after passing through the third expansion valve 11 is lower than the evaporation temperature after passing through the second expansion valve 10, so as to ensure that the low temperature is used for cooling the low-temperature stage refrigerant, so that the refrigerant is subcooled. That is, for the high temperature stage, two-way throttling is performed through the second expansion valve 10 and the third expansion valve 11 to provide different evaporation temperatures, the loop passing through the second expansion valve 10 and the condensing evaporator 2 is mainly used for cooling the low temperature stage refrigerant gas into refrigerant liquid, and functions as the low temperature stage condenser 7, and the loop passing through the third expansion valve 11, the subcooler 3 and the auxiliary compressor 12 is mainly used for providing subcooling for the low temperature stage circulation.

Comparative example 1

The conventional cascade refrigeration system consists of two refrigeration systems, namely a low-temperature stage refrigeration cycle consisting of a low-temperature stage compressor 1, a condensation evaporator 2, a low-temperature stage expansion valve 4 and an evaporator 5 and a high-temperature stage refrigeration cycle consisting of a high-temperature stage compressor 6, a condenser 7, a high-temperature stage expansion valve 13 and a condensation evaporator 2. On the basis, the conventional mechanical supercooling cascade refrigeration cycle adopts a method of additionally arranging circulation besides a low-temperature stage and a high-temperature stage to cool the refrigerant liquid from the condensation evaporator 2 in the low-temperature stage circulation, so that the supercooling degree is improved, the refrigerating capacity of the unit refrigerant flow of the low-temperature stage circulation is improved, and the total coefficient of performance (COP) of the system is improved.

As shown in fig. 3, the supercooling method of the mechanical supercooling cascade refrigeration cycle is that high-pressure refrigerant gas discharged from the outlet of the mechanical supercooling compressor 14 passes through the mechanical supercooling condenser 15, then throttled by the mechanical supercooling expansion valve 16 and enters the subcooler 3, and after absorbing heat, the mechanical supercooling refrigerant is changed into gas and enters the mechanical supercooling compressor 14 for compression.

The mechanical supercooling cycle and the subcooler 3 are arranged to further cool the low-pressure refrigerant which is circulated out of the condensing evaporator 2 in the low-temperature stage, namely, the supercooling degree of the low-temperature stage cycle is improved, and the system performance is improved. The pressure after passing through the mechanical supercooling expansion valve 16 is lower than the pressure after passing through the high-temperature expansion valve 13, that is, for the mechanical supercooling cycle, the temperature after passing through the mechanical supercooling expansion valve 16 is lower than the temperature after passing through the high-temperature expansion valve 13, so as to ensure that the low temperature is used for cooling the low-temperature refrigerant to supercool the low-temperature refrigerant. That is, for the mechanical supercooling cycle and the high-temperature stage, two paths of throttling are performed through the mechanical supercooling expansion valve 16, the subcooler 3, the high-temperature stage expansion valve 13 and the condensing evaporator 2 to provide different evaporation temperatures, a loop passing through the high-temperature stage expansion valve 13 and the condensing evaporator 2 is mainly used for cooling low-temperature stage refrigerant gas into refrigerant liquid and plays a role of the low-temperature stage condenser 7, and a loop passing through the mechanical supercooling expansion valve 16, the subcooler 3 and the mechanical supercooling compressor 14 is mainly used for providing supercooling for the low-temperature stage cycle.

Example 2

As shown in fig. 2, the present embodiment relates to a circulation system applied to a cascade refrigeration or heat pump system, which includes a flash tank 9, the flash tank 9 is respectively connected to a second expansion valve 10 and a third expansion valve 11, the second expansion valve 10 is sequentially connected to a condensation evaporator 2 and a high-temperature stage compressor 6, the third expansion valve 11 is sequentially connected to a subcooler 3 and the high-temperature stage compressor 6, and the high-temperature compressor is sequentially connected to a condenser 7 and a first expansion valve 8 and then is connected to the flash tank 9.

In addition, the circulating system also comprises two paths, namely, one path of outlet of the subcooler 3 is sequentially connected with the low-temperature stage expansion valve 4, the evaporator 5, the low-temperature stage compressor 1 and the condensing evaporator 2, and then is connected into one path of inlet of the subcooler 3 to form circulation. An outlet of the condenser 7 is sequentially connected with a first expansion valve 8 and a flash tank 9 and then connected with a high-temperature stage compressor 6, and the high-temperature stage compressor 6 is communicated with the condenser 7.

The present embodiment proposes a method of omitting the auxiliary compressor 12 from the subcooling circuit in fig. 1 based on embodiment 1, omitting the auxiliary compressor 12 from embodiment 1, and omitting the condenser 7 and the mechanical subcooling compressor 14 from the mechanical subcooling cycle from comparative example 1. The arrangement method is used for cooling the refrigerant liquid from the condensing evaporator 2 in the low-temperature stage circulation to improve the supercooling degree, thereby improving the refrigerating capacity of the unit refrigerant flow of the low-temperature stage circulation, improving the total coefficient of performance (COP) of the system, simultaneously reducing the complexity of the system and improving the arrangement of system components.

The supercooling method of the circulating system comprises the steps that one path of refrigerant liquid from the flash tank 9 enters the condensation evaporator 2 after being throttled by the second expansion valve 10 to be evaporated and absorb heat to be saturated gas, so that the low-temperature-level refrigerant gas is condensed to be saturated liquid; and the other path of refrigerant enters the subcooler 3 through the third expansion valve 11 to be evaporated and absorb heat, the high-temperature-level refrigerant is evaporated and changed into saturated gas, and the two paths of refrigerant gas are mixed and then enter the high-temperature-level compressor 6 to be compressed, so that the refrigeration cycle is completed.

Refrigerant gas from the low-temperature stage compressor 1 is condensed into saturated liquid through the condensation evaporator 2, then is changed into supercooled liquid through the supercooler 3, and then enters the evaporator 5 for evaporation and heat absorption through the isenthalpic throttling of the low-temperature stage expansion valve 4 to become saturated gas, and then enters the compressor for compression, so that the low-temperature stage refrigeration cycle is completed.

As can be seen from fig. 4, the temperature and pressure of the gas evaporated by the condenser-evaporator 2 are higher than those of the gas evaporated by the cooler 3, the mass flow rate of the high-pressure gas is higher than that of the low-pressure gas, the two gases are mixed before entering the high-temperature stage compressor 6, and the pressure of the mixed gas is slightly lower than that of the high-pressure gas, which causes a certain mixing loss at the inlet of the high-temperature stage compressor 6.

Test examples

Theoretical analysis of NH₃/CO₂The working parameters of the cascade system are set as follows: refrigerating capacity Q is 175 kW; low-temperature stage evaporation temperature T in analysis process_evaIs between-55 and-30 ℃; low temperature stage condensation temperature T_mTaking the mixture to be-16-14 ℃; supercooling degree T of low-temperature stage_subTaking the default low-temperature grade evaporation temperature T at 5-15 ℃ under the standard working condition_evaTaking a high-temperature grade condensation temperature T of minus 40 DEG C_condTaking 40 ℃ as a default, and obtaining the supercooling degree T_subTaking 10 ℃, setting the overlapping temperature difference Delta T in the condensation evaporator 2 as 5 ℃, and setting the heat exchange temperature difference Delta T in the subcooler 3_subThe temperature was taken at 2 ℃.

TABLE 1 Low-temperature stage condensation temperature T_mEffect on System COP

To calculate the degree of performance improvement of a low temperature stage subcooling cascade refrigeration system, the performance increase is expressed in normalized form as

Wherein the COP_subCOP for low-temperature level supercooling cascade refrigeration system_nscIs the COP of a conventional cascade refrigeration system.

Table 1 shows the comparison of three different cascade refrigeration systems, namely, a cascade refrigeration cycle with mechanical supercooling, a cascade refrigeration cycle with low-temperature stage supercooling (a supercooling branch does not have a compressor, the system has two compressors of high and low temperature stages), and a cascade refrigeration cycle with auxiliary compressor supercooling (a compressor is arranged at the 12 point of the supercooling branch, and the system has three compressors). The maximum COP of the three systems is 1.457, 1.461 and 1.463 respectively, the difference is not large, considering the system complexity in the maximum COP, the low-temperature stage supercooling cascade refrigeration system is provided with one less compressor than the supercooling circulation with the auxiliary compressor, the maximum COP is reduced by 0.15 percent, compared with the mechanical supercooling cascade refrigeration system, a condenser and an auxiliary compressor at a high-temperature stage are omitted, the maximum COP is increased by 0.25 percent, when the evaporation temperature is-40 ℃ and the condensation temperature is 40 ℃, the maximum COP of the low-temperature stage supercooling cascade refrigeration circulation system is 1.461 and is increased by 4.58 percent compared with the conventional cascade refrigeration system. Therefore, the low-temperature stage supercooling cascade refrigeration circulation in the three circulation systems is relatively ideal in synthesis, and the system is simplified and relatively excellent in economical efficiency.

TABLE 2 supercooling degree T_subEffect on System COP

In table 2 (discussion related to fig. 3), the COP of the low-temperature level supercooled cascade refrigeration system increases in magnitude with the increase of the supercooling degree, and when the supercooling degree increases from 5 ℃ to 15 ℃, the COP of the low-temperature level supercooled cascade refrigeration system increases from 1.434 to 1.480, which indicates that the increase of the supercooling degree has an effect of improving the system performance.

Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that various changes, modifications and substitutions can be made without departing from the spirit and scope of the present invention. Any modification, equivalent replacement, or modification made within the spirit and principle of the present invention should be included in the protection scope of the present invention.