Experimental discussion on the new Stirling cooling facility

Therefore, in order to achieve the requirements of the full temperature zone index, not only accurate design and precision machining and assembly are required, but also a large number of commissioning tests are needed to explore the operating parameters and supplement and modify the design to finally achieve the performance requirements.

2 test content and test device

2. The influence of inflation pressure on the performance of the chiller The inflation pressure is an important operating parameter of the split Stirling chiller. As a thermodynamic parameter, it affects the input of PV power and theoretical cooling power of the chiller, and also affects the aerodynamic force as a dynamic parameter. And gas damping, changing the resonance state of the whole machine operation. So we are on 1.

The suitable inflation pressure range of the 5W Stirling refrigerator has been tested and tested, which will have a certain guiding role for the mass production and commissioning of the refrigerator.

During the test, the inflator was not removed. When the refrigerator was cooled to 80K, a fixed heat load of 1.48W was input while maintaining the input power and operating frequency. Only the inflation pressure was changed, and the refrigerator was tested under the corresponding inflation pressure. The cooling temperature, by changing the influence of the inflation pressure on the cooling temperature test, find the appropriate inflation pressure range of the 1. 5W Stirling refrigerator.

When the inflation pressure is 1. 7M Pa, the compressor compressor hits the cylinder and starts the test from 1. 8M Pa.

It can be seen that when the inflation pressure is higher than 2.25M Pa, the refrigerator will not be able to maintain the required 80K refrigeration temperature. Theoretical analysis shows that as the inflation pressure increases, the gas damping gradually increases, and the damping is dissipated. The energy, it converts part of the input work into heat, and increases the temperature rise of the chiller, which is not beneficial to the chiller. In addition, the test is performed under the above setting conditions. When the inflation pressure is lower than 1. 8 MPa, the damping of the chiller system is reduced. 8MPa 2. 25M Pa. The gas pressure of the refrigerator is 1. 8MPa 2. 25M Pa.

2. 2 Cold finger spring stiffness on the performance of the chiller In order to obtain better cooling effect of the cold finger, the phase relationship between the ejector displacement and the pressure wave at the compressor outlet must be guaranteed. In the case where other parameters are fixed, the natural frequency of the ejector is the main factor affecting the phase, so the natural frequency is changed by changing the mechanical spring stiffness while ensuring the working volume of the cold chamber and the mass of the ejector, thereby achieving the resonance state. To achieve the highest refrigeration efficiency. It can be seen that when the various parameters of the compressor and other working parameters are fixed, the reasonable spring stiffness of the refrigerator ejector assembly is 3. 3N / mm 3. 7N / mm, when the spring stiffness is larger or In hours, the actual phase angle is kept away from the theoretical value, so that the cooling output value of the refrigerator is not optimal.

2. 3 The influence of operating frequency on refrigeration performance It is known that the natural frequency of the compressor is greatly affected by the gas spring force, and different inflation pressures correspond to different natural frequencies of the compressor.

When the inflation pressure is constant, the natural frequency of the compressor is constant. If the working frequency of the compressor is close to the natural frequency, the system will resonate. At this time, the displacement of the compressor mover is the largest, the current is the smallest, and the motor efficiency is high. To this end we use the current minimum method to find the proper operating frequency of the compressor. Thereby determining the operating frequency range of the refrigerator.

Select one of the compressors to fix other parameters, use the adjustable range of the driving power supply frequency, change the working frequency one by one from 45H z 60Hz, record the response current value, and find the minimum value that is the resonant frequency of the compressor.

2. The choice of 4 compressor vibrator mass and cold finger spring stiffness In the test, we found that the natural frequency changes with the different mass of the compressor mover. For this reason, the spring stiffness of the cold finger must be adjusted to match. In order to meet the requirements of the chiller performance.

3 refrigerator test results

After the above commissioning test, we determined the parameters of the inflation pressure, the mover mass, the ejector mass, the spring stiffness, the displacement, the friction pair fit clearance, and the operating frequency of the 1. 5W Stirling refrigerator. Satisfactory test results were obtained by repeating the test with these parameters. Of course, there are still many factors that affect the performance of the chiller. The above parameters are only the reference range, and some minor adjustments are still needed for each chiller to get the best results.

3. 1 cooling time

The cold head of the chiller with a heat load of 850J has a minimum time of 4 minutes and 47 seconds from normal temperature to 80K, and the longest time is 5 minutes and 30 seconds. In the case of high temperature 70, the time required for the refrigerator to drop to 80K is 7 minutes 40 seconds to 8 minutes 10 seconds under the condition that the compressor and the cold finger heat are sufficiently dissipated.

3. 2 cooling power and input power

Generally, under the same input power, the cooling power decreases with the extension of the cooling time. For example, when the cooling time exceeds 6 minutes at normal temperature, the cooling power cannot meet the index requirement. At a high temperature of 70, when the cooling time exceeds 9 minutes, the cooling capacity is difficult to meet the requirements. When the chiller is within a certain power range, the cooling power increases as the input power increases, but beyond this range, the power increase does not increase the cooling power, but increases the heat loss. Sometimes it causes a mechanical collision.

3. 3 cooling power and ambient temperature

1. 5W Stirling refrigerator requires high temperature 70 environment, with 1. 0W / 80K cooling power, foreign similar model cooling power is 0.

85W / 80K, so to achieve the cooling requirements at high temperatures, in addition to a series of measures to improve the cooling efficiency, but also good heat dissipation of the cold finger hot end.

3. 4 reliability test results

The failure mode study of the split-type Stirling refrigerator in the long-term use process at home and abroad shows that under normal conditions, the spring and motor lead inside the chiller system are fatigued, and the piston and cylinder are worn due to wear. Seal failure, working fluid pollution and working fluid leakage are the root causes of chiller failure; spring fatigue, working fluid pollution and working fluid leakage have been solved through various design and process measures. The test has also verified that these measures are completely Can guarantee the reliability requirements of the refrigerator. Therefore, in the case of a cylindrical spring-supported tactical Stirling refrigerator, the wear between the piston and the cylinder, especially between the compression piston and the compression cylinder, is the most important factor limiting reliability. The piston-cylinder motion pair can only be in the form of dry friction. The relative motion speed can be as high as the above simulation results. (1) The pressure rise of the eighth process does not depend entirely on the early opening of the intake valve. The early closing of the gas valve causes the residual low temperature working medium in the cold chamber to enter the hot chamber, which also causes the pressure to rise. The increase in the quality of the system shown in the middle can reflect the problem; (2) the effect on the indicator diagram can be seen The early closing of the exhaust valve at the low pressure and the early opening of the intake valve are far more significant than the early closing of the intake valve at the high pressure and the early opening of the exhaust valve, so the phase selection, control and optimization of this process are Especially worthy of attention.

4 Conclusion

In this paper, the movement control law of the valve-controlled regenerator and the shifting piston in the G-M refrigerator is considered. Considering the case of opening and closing the valve in advance, a research method of step-by-step modeling and simulation is proposed. It is concluded that the early closing of the exhaust valve and the early opening phase of the intake valve should be the research focus of the gas distribution scheme. Further, the above simulation can be used to study different gas distribution schemes, and the relationship between the opening and closing phase angles of the valves and the piston motion law can be effectively optimized by combining actual experience and experiments.

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