Theoretical And Experimental Investigations On The Working Mechanisms Of The Three-stage Stirling-type Pulse Tube Cryocooler

In recent years,the cryocooler working below 10 K has been widely used in the very long wave infrared detection,the THz wave detection,the millimeter wave detection,the X-ray detection and the low-Tc superconducting applications,etc.The multi-stage Stirling-type pulse tube cryocooler(SPTC)has shown strong appeal to these missions due to its advantages of low vibration,high reliability,high stability,high efficiency and long operation life.The study on this area has already been mature in some foreign countries,but it has still been faulty in China.In this way,this paper introduces the theoretical and experimental investigations on the three-stage SPTC,and the primary coverage can be concluded as follows:(1)Investigation on the dynamic characteristics of the three-stage SPTC.First,compared with the conventional electrical circuit analogy(ECA)model,the non-ideal properties of gas and the dynamic temperature are taken into consideration in this paper to establ ish a new ECA model.The distributions of the dynamic pressure and the volume flow rate in different components of SPTC are analyzed in details by a specific example.Second,the temperature profiles in regenerators are calculated quantitatively.For a three-stage gas-coupled SPTC,the simulating results indicate that the temperature profile in the first regenerator in almost linear,while in the second stage regenerator,the curve becomes non-linear at the hot end.However,in the third regenerator,the t emperature profile shows strong non-linearity,especially at the cold end.Third,the dynamic temperatures of the gas and the matrix are worked out quantitatively based on the energy conservation equations,including their amplitudes and phase angles.The simulating results display that the effect of the dynamic temperature on the ECA model in negligible when the temperature is above 70 K.And in the temperature range of 70 K-25 K,the evident difference can be observed when the dynamic temperature is ignor ed or not.However,when the temperature is below 25 K,the influence of the dynamic temperature becomes important and non-negligible.(2)Establishment of the entropy analyses model of the three-stage SPTC.The irreversible losses caused by the axial conduction,the pressure drop and the irreversible heat exchanger between gas and matrix are introduced in details,and the entropy generations produced by these three kinds of losses are calculated quantitatively.A specific example aiming at 10 K is given to provide elaborate explanations about the influences of the cooling temperature,the charging pressure,the pressure ratio,the operating frequency and the input acoustic power on the performance of the three-stage SPTC.(3)Investigation on the J-T cryocooler used to couple with the SPTC.First,a model of the J-T cryocooler precooled by a three-stage SPTC is established.The working mechanisms of the compressor,the heat exchangers,the heat sinks,the throttling device and the evaporator are discussed.Second,a pulse tube/J-T hybrid cryocooler capable of fast cool down is introduced.The structure is presented,and a dimensionless equation about the initial pressure,the exhausted pressure,the cool down time and the heat load is worked out.A specific example is used to explain the relationships between the above-mentioned parameters in details.(4)Optimizations of the three-stage thermally-coupled SPTC.Operating parameters such as the cooling temperature,the precooling temperature,the frequency,the charging pressure and the dimension parameters of the components such as the regenerator,the pulse tube,the inertance tube,the reservoir are optimized,respectively.The optimal values of the above-mentioned parameters are acquired.The simulating results indicate that the first stage SPTC can obtain a gross cooling capacity of 7.80 W/80 K when the input acoustic power is 122.24 W,where 5.02 W is used to precool the second stage SPTC and 2.75 W is used to precool the third stage SPTC.The second stage SPTC can obtain a gross cooling capacity of 1.18 W/30 K under the precooling of the first stage SPTC,when the second stage input acoustic power is 227.12 W.Under the precooling of both the first and the second stage SPTCs,the third stage SPTC can achieve a cooling capacity of 108.5 mW/10 K when the third stage input acoustic power is 51.08 W,and the no-load cooling temperature turns out to be 8.1 K.(5)Experimental investigation on the three-stage thermally-coupled SPTC.First,the experimental installation is introduced,including the vacuum insulation system,the temperature measurement system,the cooling capacity and power measurement system,the pressure measurement system and so on.Second,some key components of the three-stage SPTC is presented,such as the compressor,the aftercooler,the hot flange,the regenerator,the pulse tube,the reservoir,etc.Third,the performance of the three-stage thermally-coupled SPTC is measured,and the experimental results indicate that the single stage SPTC can obtain a gross cooling capacity of 15.66 W/80 K,when the input power is 350 W.The two-stage SPTC can obtain a gross cooling capacity of 1.43 W/30 K,when the total input power is 590 W,and the no-load cooling temperature is 17.4 K.The three-stage SPTC can obtain a cooling capacity of 38.2 mW/10 K when the total input power is 680 W,and the no-load cooling temperature turns out to be 8.9 K.The experimental results are close to the simulating ones,which turns out that the theoretical model is correct enough for use.