Research On A Single Stage Stirling Pulse Tube Cryocooler Precooled By Liquid Nitrogen

Cryocoolers have been widely required in fields like aerospace,military,superconducting electronics and medical treatment for their characteristics of simple structure,stable operation,flexible control and so on,which make them become the research hotspot of refrigeration and cryogenics.Among them,stirling pulse tube cryocoolers gradually become the ideal cryocooler in fields of military and space probe for their compactness,high reliability and long lifetime.However,due to the problems like serious loss of regenerator and pulse tube at high frequency and low temperature,the complexity of cold inertance tube phase shifting and so on,the cooling performance of stirling pulse tube cryocooler in low temperature zone below 20 K is still poor,which restricts its scope of application.In this paper,based on the inadequate researches of stirling pulse tube cryocooler around 20 K,works are carried out as follows:1.LA liquid nitrogen precooled single stage stirling pulse tube cryocooler without upper stage of regenerator is proposed and theoretically analysed its cooling performanceA liquid nitrogen precooled single stage stirling pulse tube cryocooler without upper stage of regenerator is proposed.The cryocooler is driven at low temperature by a linear compressor through a transmission tube with temperature gradient.The theoretical advantages of the precooling form are analyzed from the aspects of overall thermodynamics and energy flow in regenerator,which is promising to make the cryocooler achieve a lower refrigeration temperature and a higher cooling efficiency.Through overall simulation and optimization,a no load refrigeration temperature of 8.98 K is reached with a precooling temperature of 80 K,a charge pressure of 0.65 MPa,a working frequency of 28 Hz and an input acoustic power of 45 W.In addition,the influence of transfer tube with temperature gradient on input acoustic power and enthalpy flow is analyzed separately.The simulation indicates that the opimal cold end swept volume ratio is 15,and the optimal length to diameter ratio is 8.2.The experimental platform of the liquid nitrogen precooled single stage stirling pulse tube cryocooler was designed and built.A no load refrigeration temperature of 19.6 K was reached through experimental researches.Based on the overall simulation and optimization results,a single stage stirling pulse tube cryocooler precooled by liquid nitrogen was designed and built.The corresponding experimental investigation is carried out.By improving the thermal boundary of the transfer tube with temperature gradient and adding a water-cooled exchanger at its hot end,the problem of unstable refrigeration temperature was solved.After optimizing the operating parameters,a no load refrigeration temperature of 19.6 K was obtained with a charge pressure of 0.35 MPa,a working frequency of 28 Hz,and an input electrical power of 150 W.And it was analyzed and indicated that improving heat transfer efficiency of the precooling heat exchanger is the key for next optimization.3.The characteristics of multi-parameter coupling of cold inertance tube phase shifting are studied systematically.Preliminary experimental measurements and accuracy analysis were carried out.Based on previous studies on cold inertance tubes and simplified turbulent thermoacoustic theory,the phase shifting characristics of multi-parameter coupling in cold inertance tube are further explored.The research shows that the phase shift of cold inertance tube changes periodically along tube length,and the temperature and frequency can affect the span and peak of the cycle.There is a coupling relationship between them.Proper matching improves the phase shifting,rather than simply lowering the temperature or raising the frequency.With the same phase shifting requirement,high frequency or low temperature can make the structure more compact.When designing the inertance tube,the optimal coupling length should be determined first,then the diameter should be adjusted,which can narrow the selection range.When the structure dimension is certain,the phase shift is more sensitive at low temperature and high frequency,which requires a more precise match between operating parameters and structural parameters.So the theoretical model for designing cold inertance tubes should be as accurate as possible.In addition,the measurement system of cold inertance tube was built based on RC load method.Then the precision analysis of the measurement system is carried out,which points out the improvement direction of precise measurement for phase shift of cold inertance tubes.