Device and method for testing oil content performance of carbon dioxide heat exchanger based on air conditioning system

Abstract

The present invention belongs to the technical field of refrigeration and air conditioning technology for carbon dioxide working fluid, and specifically relates to a device and method for testing the oil content performance of a carbon dioxide heat exchanger based on an air conditioning system. The present invention includes a compressor and an oil separator, the refrigerant outlet of the oil separator is connected to the refrigerant pipeline, and the oil outlet is connected to the oil outlet pipeline; the refrigerant enters the compressor inlet after passing through a pressure differential valve, a flow regulating valve, a gas cooler, a liquid storage tank, a subcooler, a first flow meter, a throttling expansion valve, an evaporator, and a superheater in sequence; the refrigerant pipeline also includes a test branch and an intermediate heat exchanger; at the same time, an oil measurement branch for measuring the oil content by a load-bearing method is also provided; the oil outlet pipeline includes an oil reservoir, and two branch oil circuits are arranged at the outlet of the oil reservoir. The present invention can accurately measure the heat exchange of the heat exchanger at different oil contents in an air conditioning system of carbon dioxide working fluid, and ultimately provide an accurate basis for the one-to-one matching of the heat exchange and oil content of the heat exchanger.

Description

Technical Field

[0001] The present invention belongs to the technical field of refrigeration and air conditioning using carbon dioxide as a working medium, and in particular relates to a device and method for testing the oil content performance of a carbon dioxide heat exchanger based on an air conditioning system. Background Art

[0002] The automotive air conditioning system is an organic whole composed of heat exchangers, compressors, valves and other components and refrigerants. It is an essential hardware to meet the comfort of passengers in new energy vehicles and ensure driving safety. The HFC-134a refrigerant currently used in new energy vehicles has a GWP of 1300, a high global warming potential, and a prominent problem of high greenhouse effect. Carbon dioxide (CO2) is a natural working fluid with a GWP of only 1 and is harmless to the environment. It has the advantages of good heat transfer performance, low flow resistance, large cooling capacity per unit volume and good economy when used in air conditioning, and has received widespread attention from the automotive air conditioning industry in various countries around the world.

[0003] In the air conditioning system using carbon dioxide as the working fluid, the compressor is a high-speed rotating component, and lubricating oil is indispensable. However, on the one hand, when the air conditioning system is operating normally, part of the lubricating oil is brought out from the compressor along with the refrigerant gas, and will enter and remain in other components of the air conditioning system such as the heat exchanger, which not only causes the oil content of the refrigerant in the carbon dioxide system to be higher than that of the ordinary refrigerant system, thereby greatly affecting the heat exchange effect of the heat exchanger; at the same time, the above situation will also cause the compressor of the air conditioning system to have difficulty in returning oil when the vehicle conditions are harsh, and even induce compressor failure and shutdown. On the other hand, in the above air conditioning system, since there is no phase change in the gas cooler, that is, the high-pressure side heat exchanger, the temperature changes greatly during the heat exchange process, and the properties of the mixture of CO2 and lubricating oil change significantly; at this time, the density and viscosity of CO2 in the supercritical state also change greatly, and the change occurs in the second half of the gas cooler close to the critical point, which often causes the accumulation of lubricating oil there, and also significantly weakens the heat exchange performance of the gas cooler. At present, although the Chinese machinery industry standard JB / T12326-2015 "Heat Exchanger for CO2 Refrigeration System" provides a performance test method for CO2 heat exchangers for heat pumps and refrigeration equipment in an oil-free state, there is still a blank in the performance evaluation of CO2 gas coolers in air-conditioning systems with internal oil, such as new energy vehicle air-conditioning systems. In view of this, how to provide a carbon dioxide heat exchanger oil content performance test system based on air-conditioning systems, so as to solve the problem of measuring and verifying the heat exchange capacity of heat exchangers at different oil contents in air-conditioning systems with carbon dioxide working fluids, and then provide a basic basis for ensuring the accurate matching of the heat exchange capacity and oil content of heat exchangers in air-conditioning systems with internal oil, such as new energy vehicle air-conditioning systems, is a technical problem that needs to be solved in recent years in this field. Summary of the invention

[0004] One of the objects of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide a carbon dioxide heat exchanger oil content performance testing device based on an air-conditioning system, which can accurately measure the heat exchange rate of the heat exchanger at different oil contents in the air-conditioning system with carbon dioxide as the working fluid, and ultimately provide an accurate basis for the one-to-one matching of the heat exchange rate and the oil content of the heat exchanger; another object of the present invention is to provide a method based on the above-mentioned testing device, so as to further facilitate the measurement and calibration process thereof.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A device for testing the oil content performance of a carbon dioxide heat exchanger based on an air conditioning system, characterized in that it comprises a compressor and an oil separator connected to the compressor outlet, the refrigerant outlet of the oil separator is connected to the refrigerant pipeline, and the oil outlet is connected to the oil outlet pipeline; wherein:

[0007] The refrigerant in the refrigerant pipeline enters the compressor inlet after passing through the differential pressure valve PV, the flow regulating valve LV, the gas cooler, the liquid storage tank, the subcooler, the first flow meter L1, the throttling expansion valve TXV, the evaporator, and the superheater in sequence; the refrigerant pipeline also includes a test branch, the inlet end of the test branch is located on a section of the pipeline between the differential pressure valve PV and the flow regulating valve LV, and the outlet end of the test branch is located on a section of the pipeline between the gas cooler and the liquid storage tank. The test branch includes a second flow meter L2 and a carbon dioxide heat exchanger to be tested, which are arranged in sequence from the inlet end to the outlet end. The first temperature and pressure measuring point and the second temperature and pressure measuring point with temperature and pressure monitoring functions are arranged at both ends of the carbon dioxide heat exchanger to be tested respectively; an intermediate heat exchanger for heat exchange on the refrigerant side of the carbon dioxide heat exchanger to be tested is also provided on the refrigerant pipeline, and an inlet water temperature measuring point and an outlet water temperature measuring point are arranged at both ends of the intermediate heat exchanger, and a third flow meter L3 is arranged at the inlet water temperature measuring point;

[0008] An oil measuring branch for measuring the oil content by a weight-bearing method is arranged in parallel on a section of the pipeline between the subcooler and the first flow meter L1. The oil measuring branch includes a first switch valve V1, a sampling tank and a second switch valve V2 which are arranged in sequence along the refrigerant flow direction.

[0009] The oil outlet pipeline includes an oil reservoir connected to the oil outlet; two branch oil circuits are arranged at the outlet of the oil reservoir, one of which is connected to the outlet end of the second flowmeter L2 after passing through the third switch valve V3, the third temperature and pressure measuring point with temperature and pressure monitoring functions, the fourth flowmeter L4 and the oil quantity regulating valve RV in sequence; the other branch oil circuit is connected to the compressor inlet after passing through the fourth switch valve V4 and the fifth flowmeter L5 in sequence.

[0010] Preferably, the intermediate heat exchanger is a water-air heat exchanger, and the intermediate heat exchanger and the measured carbon dioxide heat exchanger are located in the same heat exchange box.

[0011] Preferably, the refrigerant pipeline further includes a fifth switch valve V5 for opening and closing the inlet end of the test branch and a sixth switch valve V6 for opening and closing the outlet end of the test pipeline.

[0012] Preferably, the refrigerant pipeline also includes a seventh switch valve V7 arranged in parallel with the oil measuring branch.

[0013] Preferably, each switch valve is a ball valve.

[0014] Preferably, the superheater is an electric superheater, and the evaporator is an electric evaporator; a fourth temperature and pressure measuring point is arranged at the outlet of the superheater.

[0015] Preferably, a method for using the carbon dioxide heat exchanger oil content performance test device based on an air conditioning system is characterized by comprising the following steps:

[0016] 1) Check the heat transfer capacity of the CO2 heat exchanger on the main and auxiliary sides:

[0017] 1.1) The intermediate heat exchanger and the tested carbon dioxide heat exchanger are fully exchanged, and the water side heat exchange capacity of the tested carbon dioxide heat exchanger is obtained by the following formula:

[0018] q=W w ·C pw (t w2 -t w1 )

[0019] in:

[0020] q is the water-side heat transfer capacity of the measured carbon dioxide heat exchanger, in W;

[0021] W w is the water flow rate measured by the third flow meter L3, in kg / s;

[0022] C pw is the specific heat of water, in J / kg℃;

[0023] t w2 is the temperature of the outlet water temperature measuring point, in °C;

[0024] t w1 is the temperature of the inlet water temperature measuring point, in °C;

[0025] 1.2) The heat transfer capacity of the refrigerant side of the tested carbon dioxide heat exchanger is obtained by the following formula:

[0026] q tco =W z ·(h1-h2)

[0027] in:

[0028] qtco is the heat transfer of the refrigerant side of the tested carbon dioxide heat exchanger, in kW;

[0029] W z is the mass flow rate of the refrigerant measured by the second flow meter L2, in kg / s;

[0030] h2 is the refrigerant enthalpy corresponding to the outlet temperature and pressure of the measured carbon dioxide heat exchanger, which can be obtained by looking up the value measured at the second temperature and pressure measuring point, and the unit is kJ / kg;

[0031] h1 is the refrigerant enthalpy corresponding to the inlet temperature and pressure of the measured carbon dioxide heat exchanger, which can be obtained by the value measured at the first temperature and pressure measuring point, and the unit is kJ / kg;

[0032] 1.3) Check the heat transfer capacity of the CO2 heat exchanger on the main and auxiliary sides:

[0033] The water side heat exchange q and the refrigerant side heat exchange q tco Take the arithmetic mean q2 and set the calibration threshold A:

[0034] When (qq tho )*100% / q2≤A, the test result is considered accurate and the data can be used; when (qq tho )*100% / q2≥A, the test result is considered inaccurate, and the leak is rechecked and the above heat transfer calculation and verification steps are repeated;

[0035] 2) Check the oil content of the CO2 heat exchanger on the main and auxiliary sides:

[0036] 2.1) The oil content Vm of the tested carbon dioxide heat exchanger is obtained by the following formula:

[0037] Vm=mo1·100% / (mo1+mf1)

[0038] in:

[0039] mo1 is the mass of oil measured by the fourth flow meter L4;

[0040] mf1 is the mass of the refrigerant measured by the second flow meter L2;

[0041] 2.2) Measure the oil content of the heat exchanger by weighing method:

[0042] Evacuate the sampling tank and weigh it to obtain the net weight mp of the sampling tank;

[0043] The sampling tank is connected to the refrigerant pipeline through the first switch valve V1 and the second switch valve V2. The two valves are opened, and the circulating working fluid formed by the mixture of oil and refrigerant in the refrigerant pipeline enters the sampling tank through the pressure difference.

[0044] Remove the sampling tank and weigh it, and get the weight of the circulating medium in the sampling tank as mpz;

[0045] Leave the sampling tank still and wait for the refrigerant in it to evaporate naturally. The oil will not evaporate and will remain in the sampling tank. Re-weigh the empty refrigerant sampling tank, and the mass is mpo.

[0046] Calculate the weight of oil as: mo2 = mpo-mp;

[0047] The oil content Vc measured by the load-bearing method is: Vc = mo2·100% / (mpz-mp);

[0048] 2.3) Check the oil content of the CO2 heat exchanger on the main and auxiliary sides:

[0049] Take the arithmetic mean Vp of the oil content Vm of the tested carbon dioxide heat exchanger and the oil content Vc measured by the load-bearing method. When (Vm-Vc)*100% / Vp≤A, the test result is considered accurate and the data can be used. When (Vm-Vc)*100% / Vp≥A, the test result is considered inaccurate, recheck for leaks and repeat the above oil content calculation and verification steps.

[0050] Preferably, the calibration threshold A is ±4%.

[0051] The beneficial effects of the present invention are:

[0052] 1) The present invention can measure the heat exchange of the carbon dioxide heat exchanger at different oil contents, thereby solving the problem of measuring the heat exchange of the carbon dioxide system heat exchanger at different oil contents. At the same time, during actual measurement, the water-air heat exchange component and its supporting measurement unit can realize the calibration function of the above heat exchange; through the oil measurement branch where the sampling tank is located, the purpose of calibrating the oil content can be achieved, and finally provide an accurate basis for the one-to-one matching of the heat exchange and oil content of the heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a schematic diagram of pipeline installation of the present invention.

[0054] The actual correspondence between the reference numerals and component names of the present invention is as follows:

[0055] a-CO2 heat exchanger under test

[0056] 10- compressor 20- oil separator 30- gas cooler 40- liquid storage tank

[0057] 50-subcooler 61-evaporator 62-superheater 70-intermediate heat exchanger

[0058] 80-sampling tank 90-oil storage 100-heat exchange box DETAILED DESCRIPTION

[0059] For ease of understanding, here we combine Figure 1 The specific structure and working mode of the present invention are further described as follows:

[0060] The specific structure of the present invention is as follows Figure 1 As shown, when the compressor 10 is working, the exhaust port, that is, the outlet, is connected to the oil separator 20. After the refrigerant of the compressor 10 passes through the oil separator 20, the oil content is theoretically less than 0.1%, and the effect of this oil content on the heat exchange can be ignored. At this time, the refrigerant outlet of the oil separator 20 is connected to the refrigerant pipeline, and the oil outlet is connected to the oil outlet pipeline; wherein:

[0061] In the refrigerant pipeline, after being regulated by the differential pressure valve PV, one refrigerant flows through the flow regulating valve LV and enters the gas cooler 30. The other refrigerant at the outlet of the differential pressure valve PV flows through the inlet ball valve as the fifth switch valve V5 and flows through the second flow meter L2 to measure the flow of the refrigerant at the test branch. Then the refrigerant flows into the first temperature and pressure measuring point, enters the refrigerant side of the tested carbon dioxide heat exchanger a and flows out, and then passes through the measurement of the second temperature and pressure measuring point, and then passes through the outlet ball valve as the sixth switch valve V6 and merges with the refrigerant at the outlet of the gas cooler 30, and flows into the liquid storage tank 40. The refrigerant at the outlet of the liquid storage tank 40 sequentially enters the subcooler 50, the liquid pipe ball valve as the seventh switch valve V7, the total pipeline flow meter as the first flow meter L1, the throttling expansion valve TXV, the evaporator 61, the superheater 62, the fourth temperature and pressure measuring point, and then enters the inlet of the compressor 10 to complete the entire refrigerant cycle.

[0062] The refrigerant flowing out of the second flowmeter L2 is pure refrigerant and does not contain oil. The oil outlet pipeline flows with pure refrigeration oil. This oil flows through the third switch valve V3 constituting the oil ball valve and flows into the third temperature and pressure measuring point, then flows through the fourth flowmeter L4, and then passes through the oil quantity regulating valve RV, and is fully mixed with the refrigerant at the outlet of the second flowmeter L2 and enters the refrigerant side of the measured carbon dioxide heat exchanger a. The other oil in the oil outlet pipeline passes through the fourth switch valve V4 and the fifth flowmeter L5, returns to the air intake port of the compressor 10, that is, the inlet, and returns to the refrigerant cycle again. Since the power of the oil flowing through the fourth flowmeter L4 comes from the pressure of the oil separator 20, and the power of the refrigerant flow flowing through the second flowmeter L2 also comes from the pressure inside the oil separator 20, under normal circumstances, the values ​​of the oil outlet of the oil separator 20 and the refrigerant outlet are the same, which leads to poor oil circulation or loss of power to adjust the flow. The present invention can make the oil outlet pressure of the oil separator 20 higher than the refrigerant outlet pressure by setting a differential pressure valve PV and adjusting the differential pressure valve PV. In this case, the oil flowing through the fourth flow meter L4 can flow more smoothly into the refrigerant pipeline after the second flow meter L2 and mix with it, and is more accurately controlled by the oil circuit regulating valve RV. In combination with the oil storage device 90 with oil storage function, it can ensure that the oil content of the carbon dioxide heat exchanger under test can be accurately adjusted from 1% to 10%. The flow regulating valve LV is used to accurately adjust the resistance ratio of the refrigerant entering the gas cooler 30 and the refrigerant entering the carbon dioxide heat exchanger under test to control the flow of the refrigerant.

[0063] The present invention also provides an intermediate heat exchanger 70, which is used to form the water side of the carbon dioxide heat exchanger a to be tested, so that the heat exchanged at the refrigerant side thereof can be taken away by water; and an inlet water temperature measuring point and an outlet water temperature measuring point with temperature monitoring function and a third flow meter L3 are provided at the same time. The intermediate heat exchanger 70 and the carbon dioxide heat exchanger a to be tested are both placed in the same heat exchange box 100, ensuring that the heat exchange amount is not lost into the environment as much as possible.

[0064] The present invention also provides a pipeline and components for measuring the oil content by the load-bearing method, namely, an oil measuring branch; the oil measuring branch includes a first switch valve V1, a sampling tank 80 and a second switch valve V2 arranged in sequence along the refrigerant flow direction. The sampling tank 80 is connected in parallel to the refrigerant pipeline through the first switch valve V1 and the second switch valve V2.

[0065] Furthermore, the calculation and verification steps of the present invention are specifically described as follows:

[0066] 1) Check the heat transfer capacity of the tested carbon dioxide heat exchanger a on the main and auxiliary sides:

[0067] 1.1) The intermediate heat exchanger 70 and the carbon dioxide heat exchanger a to be tested are fully exchanged with each other, and the water-side heat exchange capacity of the carbon dioxide heat exchanger a to be tested is obtained by the following formula:

[0068] q=W w ●C pw (t w2 -t w1 )

[0069] in:

[0070] q is the water-side heat transfer capacity of the CO2 heat exchanger a under test, in W;

[0071] W w is the water flow rate measured by the third flow meter L3, in kg / s;

[0072] C pw is the specific heat of water, in J / kg℃;

[0073] t w2 is the temperature of the outlet water temperature measuring point, in °C;

[0074] t w1 is the temperature of the inlet water temperature measuring point, in °C;

[0075] 1.2) The heat transfer of the refrigerant side of the tested carbon dioxide heat exchanger a is obtained by the following formula:

[0076] q tco =W z ·(h1-h2)

[0077] in:

[0078] q tco is the heat transfer rate on the refrigerant side of the CO2 heat exchanger a under test, in kW;

[0079] W z is the mass flow rate of the refrigerant measured by the second flow meter L2, in kg / s;

[0080] h2 is the refrigerant enthalpy corresponding to the outlet temperature and pressure of the measured carbon dioxide heat exchanger a, which can be obtained by looking up the value measured at the second temperature and pressure measuring point, and the unit is kJ / kg;

[0081] h1 is the refrigerant enthalpy corresponding to the inlet temperature and pressure of the measured carbon dioxide heat exchanger a, which can be obtained by the value measured at the first temperature and pressure measuring point, and the unit is kJ / kg;

[0082] 1.3) Check the heat transfer capacity of the tested carbon dioxide heat exchanger a on the main and auxiliary sides:

[0083] The water side heat exchange q and the refrigerant side heat exchange q tco Take the arithmetic mean value q2 and set the calibration threshold value A = ±4%:

[0084] When (qqtho )*100% / q2≤±4%, the test result is considered accurate and the data can be used; when (qq tho )*100% / q2≥±4%, the test result is considered inaccurate, and there may be other errors, such as excessive cooling leakage, inaccurate measurement of measuring points, etc. After finding the cause and correcting it, continue to repeat the above heat transfer calculation and verification steps;

[0085] 2) Check the oil content of the tested carbon dioxide heat exchanger a on the main and auxiliary sides:

[0086] 2.1) The oil content Vm of the measured carbon dioxide heat exchanger a is obtained by the following formula:

[0087] Vm=mo1·100% / (mo1+mf1)

[0088] in:

[0089] mo1 is the mass of oil measured by the fourth flow meter L4;

[0090] mf1 is the mass of the refrigerant measured by the second flow meter L2;

[0091] 2.2) Measure the oil content of the heat exchanger by weighing method:

[0092] The sampling tank 80 is evacuated and weighed to obtain the net weight mp of the sampling tank 80;

[0093] The sampling tank 80 is connected to the refrigerant pipeline through the first switch valve V1 and the second switch valve V2. The two valves are opened, and the circulating medium formed by the mixture of oil and refrigerant in the refrigerant pipeline enters the sampling tank 80 through the pressure difference.

[0094] Remove the sampling tank 80 and weigh it, and get the weight of the circulating medium in the sampling tank 80 as mpz;

[0095] Install a cotton plug on the mouth of the sampling tank 80, open it to the atmosphere, and wait for the refrigerant in it to evaporate naturally. The oil will not evaporate and will remain in the sampling tank 80. Re-weigh the sampling tank 80 that has been emptied of refrigerant, and the mass is mpo;

[0096] Calculate the weight of oil as: mo2 = mpo-mp;

[0097] The oil content Vc measured by the load-bearing method is: Vc = mo2●100% / (mpz-mp);

[0098] 2.3) Check the main and auxiliary sides of the oil content of the CO2 heat exchanger under test:

[0099] Take the arithmetic mean value Vp of the oil content Vm of the tested carbon dioxide heat exchanger a and the oil content Vc measured by the load-bearing method. When (Vm-Vc)*100% / Vp≤±4%, it is considered that the test result is accurate and the data can be used. When (Vm-Vc)*100% / Vp≥±4%, it is considered that there may be other errors in this test conducted by this device, such as refrigerant in the oil circuit, or poor oil separation effect, etc., and it is necessary to continue to find the cause, and then repeat the above oil content calculation and verification steps after correction.

[0100] To facilitate further understanding of the present invention, Table 1 provides a parameter table of one embodiment of the present invention, as follows:

[0101] Table 1

[0102]

[0103] The calculation example formed from Table 1 above is as follows; for ease of description, the unit system is not written: 1) Water side heat transfer of the tested carbon dioxide heat exchanger a:

[0104] q=W w ·C pw (t w2 -t w1 )

[0105] 9.09468 = 0.401 * 4200 * (25.1 - 19.7)

[0106] 2) The heat transfer capacity of the refrigerant side of the tested carbon dioxide heat exchanger a is obtained by the following formula:

[0107] q tco =W z ·(h1-h2)

[0108] 8.974237=0.033217*(478.49-208.32)

[0109] 3) Check the heat transfer capacity of the tested carbon dioxide heat exchanger a on the main and auxiliary sides:

[0110] The water side heat exchange q and the refrigerant side heat exchange q tco The arithmetic mean value q2 is taken, and the calibration threshold value A=±4% is set: the value of ±4% refers to the main and auxiliary deviation requirements of the national standard GB / T5773-2016 for performance testing of refrigerant compressors.

[0111] Check the oil content of the tested carbon dioxide heat exchanger a on the main and auxiliary sides:

[0112] 1) The oil content Vm of the measured carbon dioxide heat exchanger a is obtained by the following formula:

[0113] Vm=mo1●100% / (mo1+mf1)

[0114] 1.37% = 0.46 * 100% / (0.46 + 33.217)

[0115] 2) Measure the oil content of the heat exchanger by weighing method:

[0116] The sampling tank 80 is evacuated and weighed to obtain the net weight mp of the sampling tank 80;

[0117] The sampling tank 80 is connected to the refrigerant pipeline through the first switch valve V1 and the second switch valve V2. The two valves are opened, and the circulating medium formed by the mixture of oil and refrigerant in the refrigerant pipeline enters the sampling tank 80 through the pressure difference.

[0118] Remove the sampling tank 80 and weigh it, and get the weight of the circulating medium in the sampling tank 80 as mpz;

[0119] Install a cotton plug on the mouth of the sampling tank 80, open it to the atmosphere, and wait for the refrigerant in it to evaporate naturally. The oil will not evaporate and will remain in the sampling tank 80. Re-weigh the sampling tank 80 that has been emptied of refrigerant, and the mass is mpo;

[0120] Calculate the weight of oil as: mo2 = mpo-mp;

[0121] 4 = 209-205

[0122] The oil content Vc measured by the load-bearing method is: Vc = mo2●100% / (mpz-mp);

[0123] 1.37 = 4 * 100% / (285-205)

[0124] 2.3) Check the main and auxiliary sides of the oil content of the CO2 heat exchanger under test:

[0125] Take the arithmetic mean value Vp of the oil content Vm of the tested carbon dioxide heat exchanger a and the oil content Vc measured by the load-bearing method. When (Vm-Vc)*100% / Vp≤±4%, it is considered that the test result is accurate and the data can be used. When (Vm-Vc)*100% / Vp≥±4%, it is considered that there may be other errors in this test conducted by this device, such as refrigerant in the oil circuit, or poor oil separation effect, etc., and it is necessary to continue to find the cause, and then repeat the above oil content calculation and verification steps after correction.

[0126] Of course, it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, but also includes the same or similar structures that can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any reference numerals in the claims should not be regarded as limiting the claims involved.

[0127] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0128] The techniques, shapes, and structural parts not described in detail in the present invention are all well-known techniques.

Claims

1. A device for testing the oil content performance of a carbon dioxide heat exchanger based on an air conditioning system, characterized in that: It comprises a compressor (10) and an oil separator (20) connected to the outlet of the compressor (10), the refrigerant outlet of the oil separator (20) being connected to the refrigerant pipeline, and the oil outlet being connected to the oil outlet pipeline; wherein: The refrigerant in the refrigerant pipeline passes through the pressure differential valve PV, the flow regulating valve LV, the gas cooler (30), the liquid storage tank (40), the subcooler (50), the first flow meter L1, the throttling expansion valve TXV, the evaporator (61), and the superheater (62) in sequence before entering the inlet of the compressor (10); the refrigerant pipeline also includes a test branch, the inlet end of the test branch is located on a section of the pipeline between the pressure differential valve PV and the flow regulating valve LV, and the outlet end of the test branch is located on a section of the pipeline between the gas cooler (30) and the liquid storage tank (40). The test branch comprises a second flow meter L2 and a carbon dioxide heat exchanger (a) to be tested, which are arranged in sequence from the inlet end to the outlet end, and a first temperature and pressure measuring point and a second temperature and pressure measuring point with temperature and pressure monitoring functions are arranged at both ends of the carbon dioxide heat exchanger (a) to be tested; an intermediate heat exchanger (70) for performing heat exchange on the refrigerant side of the carbon dioxide heat exchanger (a) to be tested is also arranged on the refrigerant pipeline, and an inlet water temperature measuring point and an outlet water temperature measuring point are arranged at both ends of the intermediate heat exchanger (70), and a third flow meter L3 is arranged at the inlet water temperature measuring point; An oil measuring branch for measuring the oil content by a weight-bearing method is arranged in parallel on a section of the pipeline between the subcooler (50) and the first flow meter L1, and the oil measuring branch comprises a first switch valve V1, a sampling tank (80) and a second switch valve V2 which are arranged in sequence along the flow direction of the refrigerant; The oil outlet pipeline comprises an oil reservoir (90) connected to the oil outlet; two branch oil lines are arranged at the outlet of the oil reservoir (90), one of which is connected to the outlet end of the second flow meter L2 after passing through the third switch valve V3, the third temperature and pressure measuring point with temperature and pressure monitoring functions, the fourth flow meter L4 and the oil quantity regulating valve RV in sequence; the other branch oil line is connected to the inlet of the compressor (10) after passing through the fourth switch valve V4 and the fifth flow meter L5 in sequence.

2. The oil content performance testing device for a carbon dioxide heat exchanger based on an air conditioning system according to claim 1, characterized in that: The intermediate heat exchanger (70) is a water-air heat exchanger, and the intermediate heat exchanger (70) and the carbon dioxide heat exchanger (a) to be tested are located in the same heat exchange box (100).

3. A device for testing oil content in a carbon dioxide heat exchanger based on an air conditioning system according to claim 1 or 2, characterized in that: The refrigerant pipeline also includes a fifth switch valve V5 for opening and closing the inlet end of the test branch and a sixth switch valve V6 for opening and closing the outlet end of the test pipeline.

4. The oil content performance testing device for a carbon dioxide heat exchanger based on an air conditioning system according to claim 3 is characterized in that: The refrigerant pipeline also includes a seventh switch valve V7 arranged in parallel with the oil measuring branch.

5. The oil content performance testing device for a carbon dioxide heat exchanger based on an air conditioning system according to claim 4, characterized in that: Each switch valve is a ball valve.

6. A device for testing oil content in a carbon dioxide heat exchanger based on an air conditioning system according to claim 1 or 2, characterized in that: The superheater (62) is an electric superheater, and the evaporator (61) is an electric evaporator; a fourth temperature and pressure measuring point is arranged at the outlet of the superheater (62).

7. A method for using the oil content performance testing device for a carbon dioxide heat exchanger based on an air conditioning system as claimed in claim 1, characterized in that The following steps are involved: 1) Check the heat transfer capacity of the CO2 heat exchanger (a) on the main and auxiliary sides: 1.1) The intermediate heat exchanger (70) and the carbon dioxide heat exchanger (a) to be tested are fully heat exchanged, and the water-side heat exchange capacity of the carbon dioxide heat exchanger (a) to be tested is obtained by the following formula: q=W w ·C pw (t w2 -t w1 ) in: q is the water-side heat transfer capacity of the measured carbon dioxide heat exchanger (a), in W; W w is the water flow rate measured by the third flow meter L3, in kg / s; C pw is the specific heat of water, in J / kg℃; t w2 is the temperature of the outlet water temperature measuring point, in °C; t w1 is the temperature of the inlet water temperature measuring point, in °C; 1.2) The heat transfer of the refrigerant side of the tested carbon dioxide heat exchanger (a) is obtained by the following formula: q tco =W z ·(h1-h2) in: q tco is the heat transfer capacity on the refrigerant side of the CO2 heat exchanger (a) under test, in kW; W z is the mass flow rate of the refrigerant measured by the second flow meter L2, in kg / s; h2 is the refrigerant enthalpy corresponding to the outlet temperature and pressure of the measured carbon dioxide heat exchanger (a), which can be obtained by the value measured at the second temperature and pressure measuring point, and the unit is kJ / kg; h1 is the refrigerant enthalpy corresponding to the inlet temperature and pressure of the measured carbon dioxide heat exchanger (a), which can be obtained by the value measured at the first temperature and pressure measuring point, and the unit is kJ / kg; 1.3) Check the heat transfer capacity of the CO2 heat exchanger (a) on the main and auxiliary sides: The water side heat exchange q and the refrigerant side heat exchange q tco Take the arithmetic mean q2 and set the calibration threshold A: When (qq tho )*100% / q2≤A, the test result is considered accurate and the data can be used; when (qq tho )*100% / q2≥A, the test result is considered inaccurate, and the leak is rechecked and the above heat transfer calculation and verification steps are repeated; 2) Check the oil content of the tested carbon dioxide heat exchanger (a) on the main and auxiliary sides: 2.1) The oil content Vm of the tested carbon dioxide heat exchanger (a) is obtained by the following formula: Vm=mo1·100% / (mo1+mf1) in: mo1 is the mass of oil measured by the fourth flow meter L4; mf1 is the mass of the refrigerant measured by the second flow meter L2; 2.2) Measure the oil content of the heat exchanger by weighing method: The sampling tank (80) is evacuated and weighed to obtain the net weight mp of the sampling tank (80); The sampling tank (80) is connected to the refrigerant pipeline via a first switch valve V1 and a second switch valve V2, and the two valves are opened so that a circulating medium formed by a mixture of oil and refrigerant in the refrigerant pipeline enters the sampling tank (80) through a pressure difference; The sampling tank (80) is removed and weighed, and the weight of the circulating medium in the sampling tank (80) is obtained as mpz; The sampling tank (80) is left to stand, and the refrigerant therein is allowed to evaporate naturally, while the oil will not evaporate and will remain in the sampling tank (80); the sampling tank (80) from which the refrigerant has been emptied is weighed again, and the mass is mpo; Calculate the weight of oil as: mo2 = mpo-mp; The oil content Vc measured by the load-bearing method is: Vc = mo2·100% / (mpz-mp); 2.3) Check the oil content of the tested carbon dioxide heat exchanger (a) on the main and auxiliary sides: Take the arithmetic mean value Vp of the oil content Vm of the tested carbon dioxide heat exchanger (a) and the oil content Vc measured by the load-bearing method. When (Vm-Vc)*100% / Vp≤A, the test result is considered accurate and the data can be used. When (Vm-Vc)*100% / Vp≥A, the test result is considered inaccurate, and the leak should be rechecked and the above oil content calculation and verification steps should be repeated.

8. The method for testing the oil content performance of a carbon dioxide heat exchanger based on an air conditioning system according to claim 7, characterized in that: The calibration threshold A is ±4%.

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