A performance evaluation method and system for gas distribution valves used in low-frequency refrigerators

Abstract

The present invention discloses a performance evaluation method for a gas distribution valve for a low-frequency refrigerator, comprising: (1) installing a gas distribution valve to be tested at a corresponding position on an evaluation platform; the gas distribution valve to be tested includes at least one inlet valve and at least one outlet valve; (2) collecting pressure data according to a set sampling rate to obtain the pressure difference at both ends of the corresponding valve and the gas reservoir pressure; (3) obtaining the working fluid flow of the corresponding valve based on the relationship between the pressure difference at both ends of the valve and the valve working fluid flow, and obtaining the gas reservoir side mass flow using the gas reservoir pressure; (4) obtaining the flow resistance loss and leakage loss of the gas distribution valve to be tested based on the relationship between the gas reservoir side mass flow and the flow resistance loss, and the relationship between the leakage flow and the leakage loss. By using the evaluation method of the present invention, the performance test of the existing low-frequency refrigerator gas distribution valve can be quickly realized, and the internal loss distribution of the gas distribution valve can be further clarified, which plays a guiding role in the optimization of the gas distribution valve to be tested.

Description

Technical Field

[0001] The present invention belongs to the field of low-temperature refrigeration, and in particular relates to a performance evaluation method and system for an air distribution valve for a low-frequency refrigerator. Background Art

[0002] In recent years, modern scientific application technologies such as space technology, superconducting technology, cryogenic vacuum technology, infrared technology, and atomic energy technology have developed rapidly. Some key instruments and technologies need to operate more stably, faster, and more sensitively in a low-temperature environment. Therefore, there is more demand for small-sized and stable cryogenic refrigerators. This has also led to the vigorous development of small-scale cryogenic refrigerator technology, including GM refrigerators, driven by demand.

[0003] A valved low-frequency refrigerator consists of three main components: a compressor, a gas distribution valve, and a cold head. The compressor provides a high-purity working fluid (containing a small amount of oil), while the gas distribution valve converts the DC working fluid into a low-frequency alternating flow working fluid to drive the refrigerator through special structures such as the gas distribution valve, flat valve, or solenoid valve.

[0004] The analysis of the energy loss of the entire refrigerator shows that the energy loss of the system is mainly concentrated in the compressor, gas distribution valve and regenerator. Figure 1 The statistical analysis of the energy loss of the whole machine shows that the The isothermal compression loss of the compressor in the refrigerator accounts for up to 68%, followed by the loss of the gas valve, which accounts for about 22% of the total loss. The loss of the regenerator gradually increases as the refrigeration temperature decreases. When the refrigeration temperature is 22.2K, the loss of the regenerator accounts for 1% of the total loss of the whole machine. Loss of 11%.

[0005] Compared to Stirling-type high-frequency refrigerators, the regenerator in valved low-frequency refrigerators is extremely efficient, and internal refrigerator losses are primarily concentrated in the compressor and gas distribution valve. Therefore, optimizing the compressor and gas distribution valve structures in GM refrigerators can significantly improve overall refrigerator performance. Currently, there is a lack of a system for evaluating gas distribution valve performance. Summary of the Invention

[0006] The present invention provides a performance evaluation method for a gas distribution valve for a low-frequency refrigerator. This method can quickly realize the gas flow, flow resistance loss, and leakage loss of the gas distribution valve to be tested, and can play a good guiding role in the optimization of the gas distribution valve, thereby further optimizing and improving the performance of the entire refrigerator.

[0007] A performance evaluation method for a gas distribution valve for a low-frequency refrigerator comprises:

[0008] (1) Installing the gas distribution valve to be tested at a corresponding position on the evaluation platform; the gas distribution valve to be tested includes at least one inlet valve and at least one outlet valve;

[0009] (2) Collect pressure data at the set sampling rate to obtain the pressure difference at both ends of the corresponding valve and the gas reservoir pressure;

[0010] (3) According to the relationship between the pressure difference between the two ends of the valve and the working fluid flow rate of the valve, the working fluid flow rate of the corresponding valve is obtained, and the mass flow rate on the gas reservoir side is obtained using the gas reservoir pressure;

[0011] (4) According to the relationship between the mass flow rate and the flow resistance loss on the gas reservoir side, and the relationship between the leakage flow rate and the leakage loss, the flow resistance loss and leakage loss of the gas distribution valve to be tested are obtained respectively.

[0012] The gas distribution valve is a key component that connects the compressor and the expander. It is a special mechanical design that can convert DC working fluid into low-frequency alternating flow working fluid. The gas distribution valve has a variety of structures and can complete the conversion from DC to alternating flow through a variety of structures, mainly including flat rotary valves, solenoid valves and other forms of timing valves. Preferably, the gas distribution valve includes an inlet valve and an outlet valve; at a certain moment, the leakage flow rate is the smaller of the absolute values ​​of the inlet valve working fluid flow rate and the outlet valve working fluid flow rate at that moment. The inlet valve and outlet valve in the gas distribution valve can be an integrated structure or two separate valve structures.

[0013] Preferably, the relationship between the pressure difference across the valve and the valve working fluid flow rate is as follows:

[0014]

[0015] Among them is is the working fluid flow rate, K is a constant related to the valve, A0 / A h is the cross-sectional area of ​​the valve opening and the cross-sectional area of ​​the flow channel (usually taken as 0.01); ρ e is the local fluid density; △P is the pressure difference across the valve. Generally, the inner diameters of the pipes connected to the valve are the same.

[0016] Preferably, the K is obtained by the following method:

[0017] Install the inlet valve or outlet valve between the high and low pressure gas sources respectively, close the valve, detect the working fluid flow rate of the flow channel connected to the valve, and detect the pressure difference at both ends of the valve at the same time. Use formula (I) to calculate the K of the inlet valve or outlet valve d1 , K d2 , where the minimum value is taken as the K.

[0018] Preferably, K=C p A0.C pis the flow coefficient (or leakage coefficient) of the valve, and A0 is the cross-sectional area of ​​the valve opening.

[0019] Preferably, the gas reservoir side mass flow is calculated using the following formula:

[0020]

[0021] is the mass flow rate at the gas reservoir side, is the pressure change rate of the gas reservoir over time, V is the volume of the gas reservoir, R g is the gas constant, and T is the reservoir temperature. The reservoir pressure P can be used to determine the reservoir side mass flow rate.

[0022] Preferably, the relationship between the mass flow rate and the flow resistance loss on the gas reservoir side is as follows:

[0023] When the intake valve opens, the flow resistance The loss is:

[0024] when

[0025] When the outlet valve is opened, the working fluid flows through the outlet valve. The loss is:

[0026] when

[0027] Where Ntnode is the number of time nodes in one cycle of the gas distribution valve operation. is the mass flow rate on the gas reservoir side, G1 is the Gibbs free energy corresponding to a certain state of the working fluid on the high-pressure side of the gas distribution valve, G2 is the Gibbs free energy corresponding to a certain state of the working fluid on the low-pressure side of the gas distribution valve, and G3 is the Gibbs free energy corresponding to a certain state of the working fluid on the load side.

[0028] Preferably, the relationship between the leakage flow and the leakage loss is as follows:

[0029]

[0030] in, is the mass flow rate of the intake valve inlet pipeline, is the mass flow rate of the outlet pipeline of the gas outlet valve; G1 is the Gibbs free energy corresponding to a certain state of the working fluid on the high-pressure side of the gas distribution valve, and G2 is the Gibbs free energy corresponding to a certain state of the working fluid on the low-pressure side of the gas distribution valve.

[0031] A performance evaluation system for a gas distribution valve for a low-frequency refrigerator, comprising:

[0032] High-pressure side pipeline connected to the high-pressure gas source;

[0033] A low-pressure side pipeline connected to a low-pressure gas source;

[0034] The other ends of the high-pressure side pipeline and the low-pressure side pipeline of the air inlet valve and the air outlet valve are connected;

[0035] A load-side pipeline connected to the other end of the inlet valve and the outlet valve, the pipeline is provided with a valve, and the other end of the pipeline is provided with a gas reservoir;

[0036] A timing controller that controls the working cycles of the inlet and outlet valves;

[0037] At the same time, pressure sensors are provided for detecting the pressure of the high-pressure side pipeline, the low-pressure side pipeline, the load side pipeline and the gas reservoir respectively.

[0038] Preferably, the high-pressure gas source and the low-pressure gas source are provided by a gas tank or a compressor respectively, that is, during detection, the high-pressure side pipeline and the low-pressure side pipeline are directly connected to the outlet and inlet of the compressor respectively.

[0039] Principle analysis:

[0040] The gas distribution valve, a key component connecting the compressor and expander, utilizes a unique mechanical design to convert direct current (DC) fluid into a low-frequency alternating flow. These valves offer a variety of structures, including flat rotary valves, solenoid valves, and other timing valves. Due to the presence of dynamic seals, high- and low-pressure cross-flow is unavoidable, leading to leakage losses. Figure 2 This is a model diagram of the gas distribution valve. The subscripts 1, 2, and 3 refer to the pressure waves and mass flow in the high-pressure chamber, low-pressure chamber, and expander, respectively. Here is defined The flow direction is positive, The flow direction is negative.

[0041] Figure 3 It is the change of the opening coefficient (FRestrict) defined by the gas distribution valve during the intake period (Intake period), exhaust period (Exhaust period) and calm period (Peace period). During the intake period, the intake valve is open and the outlet valve is closed. The working fluid leaks from the high pressure side and the refrigerator side to the low pressure side. for:

[0042]

[0043] Here the symbol “||” means taking the absolute value.

[0044] During the exhaust phase, the inlet valve is closed, the outlet valve is opened, and the working fluid leaks from the high-pressure side to the cold head and low-pressure side. for:

[0045]

[0046] When the refrigerator is in a quiet period, the inlet and outlet valves are closed. At this time, the leakage of the gas distribution valve is approximately:

[0047]

[0048] From the combined formulas (1) to (3), it can be seen that no matter what working state the gas distribution valve is in, the leakage flow between the high and low pressure in the gas distribution valve is:

[0049]

[0050] The inlet valve and outlet valve in the gas distribution valve can be treated as nozzles. When the fluid flows through the nozzle, due to the existence of nonlinear flow resistance, the inlet and outlet pressure difference ΔP and the flow rate are nonlinear, which can be expressed by the following formula:

[0051]

[0052] Among them C d is the flow coefficient, A o / A h is the ratio of the nozzle to the flow channel cross-sectional area (generally taken as 0.01), ρ e is the local fluid density.

[0053] Theoretically, A0 can be 0, but in practice, due to manufacturing processes, it is difficult to achieve 0 when closed, and there is leakage, which in turn causes leakage loss. In actual calculations, C d A o Treat it as a constant K and directly calculate the size of K.

[0054] For the valve to be tested, K is a constant that can be obtained by Figure 4 That is, the valve to be tested (inlet valve and outlet valve) is installed between the high and low pressure gas sources, the valve is closed, and the pressure difference △P on both sides of the valve and the leakage flow rate can be obtained through the small range flow meter MFM and the differential pressure meter. According to formula (5), K when the valve to be tested is closed can be calculated d1 (intake valve) and K d2 (Outlet valve), select the smaller one as the K value. After K is obtained, in formula (5), only the pressure difference and the working fluid flow rate are unknown quantities, and the working fluid flow rate can be obtained from the pressure difference.

[0055] The schematic diagram of the gas distribution valve performance evaluation platform is shown in Figure 5The air inlet end (inlet valve) and the exhaust end (outlet valve) of the air distribution valve are connected to the high and low pressure gas sources through the high pressure side pipeline and the low pressure side pipeline respectively. The gas source can be provided by a compressor or a gas tank. The other end of the air distribution valve is connected to a pipeline with a valve R with an adjustable opening, which serves as the load section side pipeline. The other end of the pipeline is connected to a certain capacity empty volume gas reservoir C. The valve and the gas reservoir form an RC load system. By adjusting the valve opening, different load conditions can be obtained. Three high-frequency pressure sensors P1, P2, and P3 are used to monitor the pressure before and after the air distribution valve. At the same time, a high-frequency pressure sensor P4 is used to monitor the pressure of the gas reservoir C. The ideal gas state equation can be used to calculate the mass flow rate on the gas reservoir side.

[0056]

[0057] in is the time rate of change of P4 of the pressure sensor, V is the volume of the gas reservoir, R g is the gas constant, and T is the reservoir temperature.

[0058] When the intake valve opens, the flow resistance The loss is:

[0059]

[0060] Where Ntnode refers to the number of time nodes in one cycle of the valve operation. The loss is:

[0061]

[0062] The flow resistance generated when the inlet valve and outlet valve are opened during a complete operating cycle of the gas distribution valve The loss is:

[0063] Ex fric =Ex fric,1 +Ex fric, 2 (9)

[0064] Through high and low pressure gas Leakage caused Loss Ex leak for:

[0065]

[0066] The total amount of working fluid generated by the gas distribution valve Loss Ex rotary for:

[0067] ΔEx rotary =Ex leak +Exfric (11)

[0068] At this point, the theoretical model of gas flow, flow resistance loss, and leakage loss through the gas distribution valve has been completed.

[0069] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0070] By adopting the evaluation method and evaluation system of the present invention, the performance test of the existing low-frequency refrigerator gas distribution valve can be quickly realized, and the internal loss distribution of the gas distribution valve can be further clarified, which plays a guiding role in the optimization of the gas distribution valve to be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 The present invention has a valve inside the low-frequency refrigerator at different refrigeration temperatures. Loss distribution.

[0072] Figure 2 The invention discloses a gas distribution valve model for a performance evaluation method of a gas distribution valve for a low-frequency refrigerator.

[0073] Figure 3 The present invention discloses a gas distribution valve timing sequence for a method for evaluating the performance of a gas distribution valve for a low-frequency refrigerator.

[0074] Figure 4 This is the principle diagram of the test of the leakage coefficient of the valve to be tested of the present invention

[0075] Figure 5 This is a schematic diagram of the performance evaluation principle of a gas distribution valve for a low-frequency refrigerator according to the present invention.

[0076] Figure 6 This invention discloses a method for evaluating the performance of a gas distribution valve for a low-frequency refrigerator, and describes pressure fluctuations at the gas distribution valve interface.

[0077] Figure 7 The present invention provides a method for evaluating the performance of an air distribution valve for a low-frequency refrigerator and describes the flow conditions on the high- and low-pressure sides of the air distribution valve. DETAILED DESCRIPTION

[0078] like Figure 5As shown, a performance evaluation system for an air distribution valve for a low-frequency refrigerator comprises: a high-pressure side pipeline connected to the compressor outlet, the other end of the high-pressure side pipeline being connected to an air inlet valve to be tested; a low-pressure side pipeline connected to the compressor inlet, the other end of the low-pressure side pipeline being connected to an air outlet valve to be tested; the high-pressure side pipeline is connected to the other end of the low-pressure side pipeline (or is integrally arranged); a load-side pipeline connected to both the air inlet valve and the other end of the air outlet valve, a needle valve R being provided on the pipeline; an air reservoir C connected to the other end of the load-side pipeline; a timing controller for controlling the air inlet valve and the air outlet valve to close and open according to a specified timing; and pressure sensors P1 to P4 for respectively detecting the pressure of the high-pressure side pipeline at the inlet valve inlet, the low-pressure side pipeline at the outlet of the air outlet valve, the load-side pipeline, and the air reservoir.

[0079] For a gas distribution valve to be tested, the compressor of a GM refrigerator can be used as a pressure wave generator, or a gas tank can be used to provide high-pressure and low-pressure gas sources. The gas distribution valve is driven by a corresponding timing controller, and the intake and exhaust cycles are determined by the manufacturing process of the gas distribution valve and the timing controller. According to the different loads of the GM refrigerator, the volume of the gas reservoir C can be selected in the range of 1 to 10L. The needle valve R can be selected with different Cv values ​​and orifices according to different flow rates. Figure 5 As shown, at least three high-frequency pressure sensors, P1, P2, and P3, are installed at the gas distribution valve interface to monitor high-pressure, low-pressure, and load-side pressures. In addition, a high-frequency pressure sensor P4 is required to monitor pressure fluctuations within the gas reservoir.

[0080] This paper takes a remote rotary valve manufactured by the German cryo.TransMIT company as an example to evaluate the performance of the gas distribution valve.

[0081] 1. Before the experiment begins, you need to pass Figure 4 The leakage coefficient test platform shown is used to test the leakage coefficient C when the gas distribution valve is fully closed. d Conduct the test. The specific steps are as follows:

[0082] Through the gas distribution valve timing controller, the gas distribution valve is completely closed. At this time, the intake valve and exhaust valve in the gas distribution are in the cut-off state. Connect one side of the intake valve to the high-pressure gas source and the other side to the Figure 4 The flowmeter MFM shown in the figure has the exhaust valve completely blocked with a plug. Open the high-pressure gas source and measure the pressure difference ΔP and leakage flow on both sides of the valve. According to formula (5) (where A o / A h Take 0.01) to calculate the leakage coefficient C of the intake valve d1 ;

[0083]

[0084] Use a plug cap to block the intake valve in the gas distribution valve, and the exhaust valve Figure 4 Between the high-pressure gas source and the flow meter MFM, open the high-pressure gas source and repeat the above steps to obtain the leakage coefficient C of the exhaust valve. d2 The leakage coefficient of the gas distribution valve is min(C d1 , C d2 ).

[0085] 2. Connect the gas distribution valve Figure 5 The performance evaluation platform shown in the figure first turns on the timing controller to ensure that the gas distribution valve works normally according to the timing. Then the compressor is turned on. When the system pressure fluctuates stably, the pressure fluctuations at points P1, P2, P3, and P4 are recorded.

[0086] The leakage flow rate of the gas distribution valve is mainly related to P1 and P2, which can be obtained according to formula (5) and the C d A0 is calculated, that is

[0087]

[0088] For the mass flow rate at the outlet P3 of the gas distribution valve It is calculated according to formula (6).

[0089]

[0090] Figure 6 Display the pressure fluctuation of each interface of the gas distribution valve under test under a certain working condition. Figure 7 The figure shows the working medium flow through the high-pressure side and low-pressure side of the distribution valve during an operation cycle. As can be seen from the figure, the high-pressure flow is larger when the intake valve is open. After the distribution valve is closed, there is a large leakage mass flow due to the dynamic seal. Similarly, there is also a large leakage flow when the exhaust valve is closed. During the entire operation cycle, no matter the intake stage, exhaust stage or quiet period, there is inevitably leakage flow in the rotary valve. This part of the leakage flow causes the rotary valve to The loss increases, affecting the efficiency of the GM refrigerator.

[0091] 3. Combining formulas (7) to (11), it can be calculated that the flow resistance loss in the rotary valve to be tested is 762W, the leakage loss is 573W, and the total loss of the rotary valve is 1335W. The test results are basically consistent with the overall loss of the gas distribution valve of 1310W given by the simulation software Sage, which proves that the accuracy of this test method is relatively high. However, the Sage software cannot give the distribution of leakage loss and flow resistance loss inside the gas distribution valve. This method further clarifies the distribution of internal losses of the gas distribution valve. For the remoterotary valve, the leakage loss accounts for 42.9%, which is quite considerable. Therefore, it is very necessary to improve the dynamic sealing process of the gas distribution valve.

Claims

1. A performance evaluation method for a gas distribution valve for a low-frequency refrigerator, characterized in that: include: (1) Install the gas distribution valve to be tested at the corresponding position on the evaluation platform; The gas distribution valve to be tested includes an air inlet valve and an air outlet valve; (2) Collect pressure data according to the set sampling rate to obtain the pressure difference at both ends of the corresponding valve and the gas reservoir pressure; (3) According to the relationship between the pressure difference at both ends of the valve and the working fluid flow rate of the valve, the working fluid flow rate of the corresponding valve is obtained, and the mass flow rate on the gas reservoir side is obtained using the gas reservoir pressure; (4) Based on the relationship between the mass flow rate and the flow resistance loss on the gas reservoir side, and the relationship between the leakage flow rate and the leakage loss, the flow resistance loss and leakage loss of the gas distribution valve to be tested are obtained respectively; The leakage flow rate is the smaller of the absolute values ​​of the inlet valve working fluid flow rate and the outlet valve working fluid flow rate; The relationship between the mass flow rate and flow resistance loss on the gas reservoir side is as follows: When the intake valve is open, the exergy loss caused by its flow resistance is: ; When the outlet valve is open, the exergy loss caused by the working fluid flowing through the outlet valve is: ; Where Ntnode is the number of time nodes in one cycle of the gas distribution valve operation. is the mass flow rate at the gas reservoir side, is the Gibbs free energy corresponding to a certain state of the working fluid on the high-pressure side of the valve, is the Gibbs free energy corresponding to a certain state of the working fluid on the low-pressure side of the valve, is the Gibbs free energy corresponding to a certain state of the working fluid on the load side; The relationship between the leakage flow rate and the leakage loss is as follows: ; in, is the mass flow rate of the intake valve inlet pipeline, is the mass flow rate of the outlet pipeline of the gas outlet valve; is the Gibbs free energy corresponding to a certain state of the working fluid on the high-pressure side of the valve, is the Gibbs free energy corresponding to a certain state of the working fluid on the low-pressure side of the distribution valve.

2. The performance evaluation method for a gas distribution valve for a low-frequency refrigerator according to claim 1, characterized in that: The relationship between the pressure difference at both ends of the valve and the valve working fluid flow rate is as follows: （I） Among them is is the working fluid flow rate, K is a constant related to the valve, A0 / A h is the valve opening cross-sectional area and the flow channel cross-sectional area; ρ e is the local fluid density; △P is the pressure difference across the valve.

3. The performance evaluation method for a gas distribution valve for a low-frequency refrigerator according to claim 2, characterized in that: The K is obtained by the following method: Install the inlet valve or outlet valve between the high-pressure and low-pressure gas sources respectively, close the valve, detect the working fluid flow rate in the flow channel connected to the valve, and detect the pressure difference at both ends of the valve at the same time. Use formula (I) to calculate the K of the inlet valve or outlet valve d1 , K d2 , where K d1 , K d2 The smaller value is used as the K.

4. The performance evaluation method for a gas distribution valve for a low-frequency refrigerator according to claim 1, characterized in that: The mass flow rate on the gas reservoir side is calculated using the following formula: ， is the mass flow rate at the gas reservoir side, is the pressure change rate of the gas reservoir over time, V is the volume of the gas reservoir, R g is the gas constant, and T is the reservoir temperature.

Images