Theoretical And Experimental Research On The Influence Of Compressor Driving Mode On The Performance Of 2-stage Pulse Tube Refrigerator Operating At 20 K

Usually,the multi-stage cryogenic for infrared detectors in the low-temperature range from 150 K to near absolute zero is required.In recent years,with increasing detection accuracy and wavelengths,the operating temperature of the detection system has been gradually reduced.Without moving parts at low temperatures,the two-stage stirling-type pulse tube cooler has the advantages of long life and high reliability.The two-stage pulse tube refrigerator can provide the precooling of the front stage and the refrigeration of the liquid hydrogen temperature zone,which makes it the best choice as a part of the multi-stage cooling system for cooling from room temperature to the liquid hydrogen temperature zone.The driving mode of the thermal coupled two-stage pulse tube refrigerator can be a single compressor or double compressors.The structure of the double compressor is complex,the weight and volume are large.The refrigeration performance of a single compressor is reduced due to the same operation parameters of 2 cold fingers working at different temperatures.The cooling capacity of the two stages cannot be flexibly adjusted.However,the advantages of lower weight and volume make the two-stage pulse tube refrigerator driven by a single compressor more valuable for space application.The structure parameters of the two-stage cold finger have been designed by our group,which is driven by double compressors.To improve the refrigeration performance of a two-stage pulse tube refrigerator driven by a single compressor,with the designed structure parameters,the following work is carried out in this paper:1)The operating parameters of the 1st-stage cold finger driven by double compressors are 3.2 MPa,50 Hz,and the operating parameters of the 2nd-stage cold finger are 2 MPa,40 Hz.The influence of operating parameters on the refrigeration performance of the two-stage cold finger was studied.The performance of the first stage and the second stage cold finger at the operating parameters of 35 Hz,40 Hz,45 Hz and 2.4 MPa,2.8 MPa,3.2 MPa were tested under the double compressors.The1st-stage refrigeration efficiency is better under higher pressure and higher frequency,while the 2nd-stage refrigeration efficiency is better under lower pressure and lower frequency,which shows the performance trend is opposite at 2 different cooling temperatures.Considering the compressor scavenging volume limitation and refrigeration performance at different operating paraments,the operation parament of40 Hz and 2.8 MPa is the chooser.The refrigeration performance of 6.7 W @ 80 K and 0.37 W @ 20 K can be obtained at 400 W input power.2)The compressor connects two cold fingers through a three-way branch pipe.To optimize the structure of the branch pipe and reduce the acoustic power loss,the calculation results of the impedance,the acoustic power loss,and the acoustic power distribution of the three-way branch pipe are corrected by fluent numerical simulation of a three-dimensional model,which is consistent with the experimental results.The acoustic power loss of Y-type branch pipe with branch pipe angles of 30 °,45 ° and90 ° is calculated.The acoustic power loss is reduced when the branch pipe angle is smaller,which is consistent with the experimental results.When the input electric power is 400 W,changing the structure of the branch pipe from the original T-type to30 ° Y-type,the acoustic power loss at the tee joint is optimized from 44 w to 24 W.The refrigeration performance of 11.9 W @ 80 K and 0.57 W @ 20 K is achieved,with the input electric work of 400 W,and rCOP is 9.64%.The refrigeration performance of 0.4 W @ 20 K and 9 W @ 80 K is achieved under the input electric work of 320 W,and the rCOP is 8.99%.The rCOP is higher than that driven by double compressors of the same cooling capacity after optimizing the operation parameters,inlet connection,and phase modulation parameters.3)Based on the thermoacoustic impedance model,the influence of the length of the 1st-stage inertance tube,the stroke,and the phase of the 2nd-stage phasor piston on the impedance are studied.The experimental results show that the impedance and acoustic power distribution of the cold finger can be adjusted by changing the phasor parameters of each stage.When the input electric power of the compressor is 320 W,the first stage loses 1.5 W cold capacity at 80 K,and the second stage increases 0.015 W cold capacity at 20 K,while the length of the first inertia tube of the first stage cold finger is increased by 0.4 m from the optimal value.The acoustic power distribution of the two cold fingers can be adjusted,with the cost of the large reduction of refrigeration performance.The cooling capacity of each temperature region should be considered when designing a two-stage pulse tube refrigerator driven by a single compressor.The acoustic power distribution and cooling capacity distribution of the cold finger can be adjusted by optimizing the structural parameters of two cold fingers.