CN106257054B - The model building method and detection device of GM refrigerator compressor units - Google Patents

Abstract

The invention discloses a method for constructing a model of a compressor unit of a GM refrigerator, comprising: testing the mass flow rate and the suction and discharge pressure of the compressor unit of a GM refrigerator to be detected under different suction and discharge pressures of the compressor unit of a GM refrigerator and power consumption, to obtain the functional relationship between the volumetric flow rate and the pressure ratio of the compressor unit of the GM refrigerator, and the functional relationship between the efficiency and the pressure ratio; obtain the high-pressure volume and low-pressure volume of the compressor unit of the GM refrigerator, and complete the GM Determination of model parameters for a refrigerator compressor unit. The present invention will analyze and fit the flow rate, efficiency and volume distribution of the compressor based on the actually measured data of the compressor to form a compressor model for simulating the performance of the compressor under different working conditions; Based on the model of the compressor, the cold head of the GM refrigerator can be optimally designed, and the model constructed can better reflect the performance of the actual refrigerator.

Description

Model building method and detection device for GM refrigerator compressor unit

technical field

The invention belongs to the field of low-temperature refrigeration, and in particular relates to a model building method and a detection device for a compressor unit of a GM refrigerator.

Background technique

With the rapid development of cryogenic vacuum, small helium liquefier and low temperature superconducting technologies, the demand for small cryogenic refrigerators is increasing day by day. In these industries, the low-temperature refrigerators that have been applied in large quantities are currently only GM refrigerators. Compared with GM refrigerators, GM type pulse tube refrigerators have outstanding advantages such as no moving parts at low temperature, simple structure, high reliability, low mechanical vibration and electromagnetic noise, etc. In applications requiring extremely low vibration, It can be an alternative model of GM refrigerator. GM type pulse tube refrigerator and GM refrigerator (hereinafter collectively referred to as GM type refrigerator) use the same compressor, and the cold head and compressor are connected by high and low pressure switching valves. The gas alternating frequency of the cold head is usually 1-2Hz. Compared with the Stirling type refrigerator whose operating frequency is tens or even hundreds of Hz, the GM type refrigerator can obtain a higher pressure ratio, and the heat exchange between the gas working medium and the regenerative packing in the regenerator is more sufficient. , so that it is easier to obtain a lower refrigeration temperature. Although GM refrigerators have been commercialized, their cooling efficiency still needs to be improved.

Radebaugh (RADEBAUGH R. Stirling and Gifford McMahon Cryocoolers [R]. Hangzhou: Institute of Refrigeration and Cryogenics, Zhejiang University, 2015) pointed out that the efficiency of the compressor used in GM refrigerators (GM compressor for short) is usually 50% about. For an actual compressor, its efficiency often changes with the change of suction and discharge pressure conditions.

When a compressor is used in a cryogenic refrigerator system, the amount of gas contained in the compressor will decrease as the temperature of the cold head decreases. The reason is that after the temperature of the cold head drops, the gas density increases, and the gas in the whole system will enrich the cold head. Therefore, when the GM type refrigerator is cooling at different temperatures, the working conditions of its compressor will also change, which will have a great impact on its efficiency. For such applications, there is currently no method for simulating the performance of this type of compressor under various operating conditions.

Compared with the previous method, some people have tested the compressor and used it as a reference to design the refrigerator, but failed to summarize the flow and efficiency characteristics of the compressor (independent of the charging pressure), and did not take into account the impact of the internal volume distribution of the compressor on The effect of the refrigerator as a whole. For the simulation design of the refrigerator, the previous research methods did not consider the influence of the performance change of the compressor, and always assumed that the high and low pressures were fixed, or the pressure wave input to the cold head of the refrigerator was fixed, or even simplified as A piecewise linear function, as shown in Figure 1. Therefore, these simulation methods can only simulate the results within a small range of operating conditions, and cannot reflect the performance of the refrigerator in different operating environments.

Contents of the invention

The present invention provides a model building method for the compressor unit of a GM refrigerator, which fully considers the structural characteristics and working performance characteristics of the compressor unit of the GM refrigerator, and constructs a compressor model that changes dynamically with the system, which can accurately simulate the operation of the refrigerator. Overall machine performance at different cooling temperatures.

The present invention also provides a model parameter detection device for the compressor unit of the GM refrigerator. With the device, the dynamic model parameters for constructing the compressor unit of the GM refrigerator can be quickly detected, and a model more in line with the actual operating conditions of the refrigerator can be constructed. .

A method for building a model of a compressor unit of a GM refrigerator, comprising:

Under different suction and discharge pressures of the compressor unit of the GM refrigerator, test the mass flow rate, suction and discharge pressure, and power consumption of the compressor unit of the GM refrigerator to be tested, and then proceed as follows:

(a) Obtain the volume flow, efficiency and pressure ratio corresponding to each suction and exhaust pressure, and fit the functional relationship between the volume flow and pressure ratio of the compressor unit of the GM refrigerator, as well as the functional relationship between efficiency and pressure ratio Mode;

(b) Fit the suction pressure data or the discharge pressure data with the pressure difference data between the two, calculate the high-pressure volume and low-pressure volume of the compressor unit of the GM refrigerator, and complete the model parameters of the compressor unit of the GM refrigerator ok.

During the model building process of the present invention, the compressor can be measured under different initial inflation pressure states to obtain multiple sets of data, so that the fitting result or volume calculation result is more accurate. The selection of the initial charging pressure state can be selected near the initial charging pressure state required by the refrigerator system, which can be greater than, equal to or less than this value. For example, if the inflation pressure of the refrigerator system is 1.7MPa, 1.7MPa, 1.6MPa, etc. 1.5MPa can be selected.

The model constructed by the present invention includes three main characteristic relationships: (1) the relationship between volumetric flow and pressure ratio; (2) the relationship between efficiency and pressure ratio; (3) and the high pressure volume and low pressure of the GM refrigerator compressor unit Volume and other parameters. Based on these three characteristics, the compressor model can be obtained through programming or with the help of third-party software applications, such as Sage, to simulate its performance under different working conditions to determine its parameters such as flow, pressure and efficiency.

The present invention also provides a model parameter detection device for a compressor unit of a GM refrigerator, comprising:

The regulating valve used to adjust the suction and discharge pressure of the compressor unit of the GM refrigerator;

Mass flow meters for measuring the mass flow of GM refrigerator compressor units;

A power meter for measuring the electrical power consumed by the compressor unit of the GM refrigerator;

And two pressure gauges for detecting the suction and discharge pressure of the compressor unit of the GM refrigerator;

The regulating valve and the mass flowmeter form a loop with the suction and exhaust port of the GM refrigerator compressor unit through the pipeline, the regulating valve is set close to the air outlet of the compressor unit, and the mass flowmeter is set close to the suction port of the compressor unit; of course , the order of the mass flowmeter and the regulating valve does not have to be arranged in the above way, and the positions can be exchanged, depending on the calibration range of the flowmeter.

Preferably, the suction and exhaust ports of the compressor unit of the GM refrigerator are respectively connected to a mass flow meter or a regulating valve through a metal hose. For the setting of the pressure gauge, it is better that the pressure gauge can directly detect the pressure of the compressor intake and exhaust, and try to minimize the influence of the connecting pipeline when arranging, that is, it should be respectively arranged at the exhaust port of the high-pressure metal hose, and the inlet of the low-pressure metal hose. Preferably, according to the gas flow direction, two pressure gauges are respectively placed on the pipeline connected to the suction port of the regulating valve and on the pipeline where the gas outlet of the flowmeter is located.

Preferably, the volume flow rate is calculated from the mass flow rate and the gas density in an inhalation state. As a positive displacement compressor, its suction volume flow should have nothing to do with the charging pressure in theory, because the suction flow is mainly determined by the suction volume of the compressor. Its inspiratory flow is defined as the ratio of the mass flow to the gas density in the inspiratory state:

in, Is the mass flow rate, T _l and p _l represent the gas temperature and pressure in the inspiratory (or inspiratory) state, respectively.

COP is an important performance index of a refrigerator. If a model is to be used to simulate the COP of a refrigerator under different operating conditions, it is necessary to first simulate the efficiency of the compressor under different operating conditions. Because it is found in actual experiments that the suction and discharge temperatures of the compressor are almost the same as the room temperature, the three are assumed to be the same in the model. According to the first and second laws of thermodynamics, the output of the compressor can be defined as:

is the mass flow rate, h(p, T) is the enthalpy value of helium corresponding to pressure p and temperature T, s(p, T) is the corresponding entropy value of helium, subscript h indicates high pressure (compressor discharge pressure ) state, l represents the low pressure (compressor suction pressure) state, and 0 represents the ambient state.

Efficiency (i.e. compressor efficiency) can be expressed as the compressor output and its input power (power consumption ) ratio:

Through the analysis and processing of the measured data, the relationship between the compressor suction flow rate or efficiency and the pressure ratio can be obtained. The relationship between the suction volume flow rate and the pressure ratio is almost independent of the inflation pressure when the compressor is working stably. Polynomial fitting obtains the relationship between volume flow or efficiency and pressure ratio, as follows:

f(x)＝C ₀ +C ₁ x+C ₂ x ² +…+C _n x ⁿ (4)

The value of n can be reasonably selected according to the data processing results, and the values of C ₀ , C ₁ ... C _n can be obtained by fitting, so as to determine the relationship between volume flow and pressure ratio. This relation has nothing to do with the charging pressure. When the compressor model is used in the simulation of the refrigerator, this formula is also applicable, because it will not be affected by the change of the compressor working condition caused by the temperature drop of the cold head, and it can also predict the temperature of the refrigerator under different cooling conditions. performance at temperature.

Preferably, for the pressure gauge for measuring the exhaust pressure, the relationship between the pressure data and the pressure difference is a first-order function, and its slope is:

k _h =V _l /(V _l +V _h ) (A1)

For the pressure gauge measuring the suction pressure, the relationship between the pressure data and the pressure difference is a first-order function, and its slope is:

k _l ＝-V _h /(V _l +V _h ) (A2)

According to formula (A1) or formula (A2), combined with the total volume of the compressor unit of the GM refrigerator, the internal high-pressure volume V _h and low-pressure volume V _l of the compressor unit of the GM refrigerator are obtained.

For the current GM-type pulse tube refrigerator, the compressor unit packaging mainly contains components such as pressure packs, water-cooled heat exchangers, oil separators, and adsorbers. These components all have a certain volume that cannot be ignored, but they cannot be completely Find out the exact value. However, the models constructed in the prior art generally do not consider these components, resulting in very low model accuracy. According to the present invention, these volumes can be simplified into two parts, namely high pressure volume and low pressure volume, and the volume distribution in the compressor can be determined by analyzing the pressure parameters.

The total volume of the compressor can be calculated by filling a certain amount of gas working fluid into the compressor and calculating it according to the pressure change before and after filling. To simplify the analysis, the following assumptions are made:

1. Helium is an ideal gas;

2. The internal pressure and temperature of the high and low pressure volumes are uniform, and the temperature is the same as the room temperature;

3. Hulu compression chamber volume.

According to the ideal gas state equation,

p _h V _h = n _h RT ₀ (5)

p _l V _l = n _l RT ₀ (6)

p _f (V _h +V _l )＝(n _h +n _l )RT ₀ (7)

where V is the volume, n is the molecular weight, R is the gas constant, and the subscript f indicates the gas-filled state at the same temperature as the environment. Through the above three formulas, the high and low pressure can be expressed as a function of pressure difference:

Δp=p _h -p _l (10)

It can be seen that there is a linear relationship between the high and low pressure and the pressure difference, which is consistent with the experimental data. Each set of experimental data can be fitted to obtain the slope, and the average value can be calculated, and the volume distribution in the compressor can be calculated according to the expression of the slope in formula (8) or formula (9). In the test system, V _h and V _l each include the volume of the metal hose, which are the sum of the high-pressure volume in the compressor and the high-pressure metal hose and the sum of the low-pressure volume in the compressor and the low-pressure metal hose, as follows:

V _h =V _hb +V _hl (11)

V _l =V _lb +V _ll (12)

The sum of the high pressure volume and low pressure volume in the compressor is the total volume of the compressor as follows

V _hb + V _lb = V _com (13)

Among them, the metal hose can be approximated as a smooth straight pipe to calculate its volume (with known pipe length and inner diameter). From this, it can be obtained that the volume distribution inside the compressor unit can be determined. The clarification of this characteristic can make the overall simulation of the refrigerator closer to the actual performance of the refrigerator, because it can accurately simulate the operation of the refrigerator. The mass of helium working fluid contained in it.

The present invention will analyze and fit the flow rate, efficiency and volume distribution of the compressor based on the actually measured data of the compressor to form a compressor model for simulating the performance of the compressor under different working conditions; Based on the model of the compressor, the cold head of the GM refrigerator can be optimally designed, and the model constructed can better reflect the performance of the actual refrigerator.

Description of drawings

Figure 1 shows the pressure waveform design of an existing refrigerator.

Fig. 2 is a schematic structural diagram of a model parameter detection device for a compressor unit of a GM refrigerator according to the present invention.

Fig. 3 is a graph showing the relationship between the inspiratory volumetric flow rate and the pressure ratio obtained in the examples.

Fig. 4 is the relationship diagram of the efficiency and the pressure ratio obtained in the embodiment part.

Fig. 5 is a diagram showing the variation of pressure with pressure difference obtained in the embodiment part.

Fig. 6 is a comparison (32.9K, 2.3Hz) diagram of the pressure waveform calculation result obtained in the embodiment part and the experimental result.

Fig. 7 is a comparison (76.5K, 2.3Hz) diagram of the pressure waveform calculation results obtained in the embodiment part and the experimental results.

Fig. 8 is a comparison diagram of the simulation and experiment of the variation of cooling capacity obtained in the embodiment part.

Fig. 9 is a comparison diagram of the simulation and experiment of the temperature change of COP refrigeration obtained in the embodiment part.

Fig. 10 is a structural schematic diagram of the refrigerator used in the experiment of the embodiment part.

Detailed ways

Example 1

Taking the compressor RW2 as an example, its packaging contains components such as a pressure bag, a water-cooled heat exchanger, an oil separator, and an adsorber. The compressor is selected for testing, and the inflation pressure of the pulse tube refrigerator driven by it is generally 1.7MPa. Accordingly, three groups of inflation pressures of 1.7MPa, 1.6MPa and 1.5MPa were selected for testing. Set up the test system as shown in Figure 2. The RW2 compressor unit is connected with the metal hose 2, the regulating valve 4, the mass flow meter 5 and the metal hose 2 through the air circuit in sequence to form a loop. The suction and discharge pressure of the compressor is adjusted through the regulating valve 4, the mass flow meter 5 measures the mass flow rate, the power consumption of the compressor is measured by the power meter 6, and the suction and discharge pressure is measured by two pressure gauges (respectively pressure gauge 3a and pressure gauge 3b, the pressure gauge 3a is used to measure the discharge pressure of the compressor, and the pressure gauge 3b is used to measure the suction pressure of the compressor), which are respectively placed before the regulating valve and after the flowmeter. From this, the mass flow rate within a certain pressure difference range and the corresponding electric work consumed by the compressor are measured.

According to formula (1), the suction temperature is taken as 300K, and the volume flow rate corresponding to each mass flow rate is calculated, as shown in Figure 3. It can be seen that the inspiratory volume flow has nothing to do with the inflation pressure, and has almost a linear relationship with the pressure ratio. Thus, according to (4), select n=1, and fit the curve in Fig. 3 to obtain the relationship diagram between the inspiratory volume flow rate and the pressure ratio:

According to formulas (2) and (3) to process the data, the relationship between efficiency and pressure ratio can be obtained as shown in Figure 4. For this image, choose n=3, and the relationship between the fitting efficiency and the pressure ratio is:

η _ex,r ＝-1.575+3.201P _r -1.712P _r ² +0.288P _r ³ (15)

During the process of controlling the regulating valve, the change of the pressure condition can be recorded, as shown in the middle point of Figure 5. The slopes of the high pressures can be obtained by linear fitting of the pressure of the high pressure group, which are 0.552, 0.536 and 0.507, respectively. Take the average of the three and combine Equation (8) (slope), Equations (11) and (13), and the total compressor volume (9.57 liters), metal hose length (4.5 meters) and diameter (0.012 meters) , it can be calculated that the high-pressure volume and low-pressure volume in the compressor are 4.45 and 5.12 liters respectively.

Based on the above three characteristics ((1) the relationship between suction volume flow and pressure ratio; (2) the relationship between efficiency and pressure ratio; (3) high pressure volume and low pressure volume), with the help of the third-party commercial software, Sage, the compressor can be and the complete refrigeration machine for simulation.

The obtained results can accurately simulate the change of the pressure waveform with the cooling temperature, as shown in Figure 6 and Figure 7, which shows that when the temperature of the cold head changes, the overall average pressure of the system increases, the impedance of the cold head increases, and the compressor pressure ratio increases.

It can also accurately simulate the cooling capacity and the COP of the whole machine (as shown in Figure 10), that is, the cooling capacity divided by the input power, as shown in Figure 8 and Figure 9, can accurately simulate the cooling capacity of the whole machine at different cooling temperatures The performance also reflects the reliability of the compressor simulation. As the cooling temperature increases, it can be seen that the cooling capacity and COP do not show an absolute linear change with the temperature. This is also because the pressure ratio increases and the mass flow rate decreases as the cooling temperature increases. At the same time, the slope also gradually decreases.

The present invention has carried out experimental test to RW2 compressor, obtains following main conclusion according to the data analysis that measures:

1. The compressor can be simplified as a model composed of three characteristics: flow rate, efficiency and volume distribution;

2. Inspiratory volume flow and Efficiency can be fitted as a function of pressure ratio, independent of inflation pressure;

3. The volume distribution in the compressor has a great influence on the pressure working condition of the system. The method for estimating the volume distribution is proposed in the present invention and verified.

Based on the model of the compressor, the cold head of the GM type refrigerator can be optimally designed, and the obtained results will better reflect the performance of the actual refrigerator.

Claims (7)

1. A method of model building a GM refrigerator compressor unit, comprising:

testing the mass flow, the air suction and exhaust pressure and the electric power consumption of the GM refrigerator compressor unit to be detected under the air suction and exhaust pressure of different GM refrigerator compressor units, and then carrying out the following processing:

(a) solving the corresponding volume flow, efficiency and pressure ratio under each air suction and exhaust pressure, and fitting to obtain a functional relation of the volume flow and the pressure ratio of the GM refrigerator compressor unit and a functional relation of the efficiency and the pressure ratio;

(b) fitting the air suction pressure data or the exhaust pressure data with the pressure difference data of the air suction pressure data and the exhaust pressure data to obtain the high-pressure volume and the low-pressure volume of the GM refrigerator compressor unit so as to complete the determination of the model parameters of the GM refrigerator compressor unit.

2. The method of modeling a GM refrigerator compressor unit of claim 1, wherein the volumetric flow rate is calculated from the mass flow rate and the gas density in the suction state.

3. The method of model building for a GM refrigerator compressor unit of claim 1 wherein the efficiency is given by the formula:

wherein:

for mass flow, h (p, T) is the enthalpy of the helium gas corresponding to the pressure p and temperature T, s (p, T) is the entropy of the corresponding helium gas, subscript h represents the discharge state of the GM refrigerator compressor unit, l represents the suction state of the GM refrigerator compressor unit, 0 represents the ambient state;to consume electrical power;for output of compressor

4. The method of modeling a GM refrigerator compressor unit of claim 1 wherein the pressure data and differential pressure are first order functional relationships with respect to suction or discharge pressure, and the absolute values of the slopes are:

slope k for exhaust pressure_hSatisfies the following conditions:

|k_h|＝V_l/(V_l+V_h)

slope k for inspiratory pressure_lSatisfies the following conditions:

|k_l|＝V_h/(V_l+V_h)

wherein V_lIs a low pressure volume, V_hA high pressure volume;

according to the above formula, the high pressure volume and the low pressure volume of the GM refrigerator compressor unit are obtained by simultaneously combining the total volume of the GM refrigerator compressor unit.

5. The method of model building for a GM refrigerator compressor unit of claim 1 wherein the GM refrigerator compressor unit is measured at different initial inflation pressure conditions to obtain multiple sets of data for fitting.

6. A model parameter detection device for a GM refrigerator compressor unit, comprising:

a regulating valve for regulating the suction and exhaust pressure of the GM refrigerator compressor unit;

the mass flow meter is used for measuring the mass flow of the GM refrigerator compressor unit;

a power meter for measuring the power consumed by the GM refrigerator compressor unit;

two pressure gauges for detecting the suction and exhaust pressures of the GM refrigerator compressor unit;

and the regulating valve and the mass flow meter form a loop with a suction and exhaust port of a GM refrigerator compressor unit through a pipeline.

7. The GM refrigerator compressor unit model parameter detection apparatus of claim 6, where the GM refrigerator compressor unit suction and exhaust ports are connected to a mass flow meter or a regulating valve through metal hoses, respectively.