Theoretical And Experimental Research On The Thermodynamic Characteristics Of Stirling/Pulse Tube Hybrid Cryocooler Operating At 30K

As a novel cryocooler proposed in the early 21^st century,Stirling/pulse tube hybrid cryocooler shows great potential in deep low temperature space detection applications due to its numerous advantages of high efficiency,high reliability,compact structure and inter-stage cooling capacity active allocation.Stirling/pulse tube hybrid cryocooler is composed of a Stirling cryocooler as the first stage and a pulse tube cryocooler as the second stage.The hybrid cryocooler combines the advantages of high efficiency and compact structure of Stirling cryocooler and high reliability of pulse tube cryocooler,and makes both stages operate in their respective appropriate conditions through reasonable structural and thermodynamic design.Thus,the hybrid cryocooler makes the high efficiency no longer contradicts with the long life.Moreover,the cooling capacity of both stages in the hybrid cryocooler can be shifted through the active shifting of the displacer,which makes the hybrid cryocooler suitable for the environment where external load changes.However,the research related to the theoretical model and thermodynamic characteristics of the hybrid cryocooler is hardly found in the open articles,which restricts the development,promotion and application of the hybrid cryocooler seriously.Based on the analysis above,this thesis attempts to analyze the thermodynamic characteristics of the hybrid cryocooler deeply through establishing a theoretical model,and research the relationship among the thermodynamic parameters,structural dimensions and operating conditions.The theoretical model and related analysis results are verified numerically and experimentally.The details of the research are shown as follows:1)Establish the theoretical model of Stirling/pulse tube hybrid cryocooler.The theoretical model of Stirling/pulse tube hybrid cryocooler is established according to the linear thermoacoustic theory and the thermodynamic process relations.The theoretical model divides the hybrid cryocooler into two types of control volume.According to the type of control volume,thermoacoustic equations and thermodynamic process relations are respectively adopted to give the analytical expressions of pressure wave and volume flow in various control volumes.Then,the relationship among the cooling performance,structural dimensions and operating conditions can be presented explicitly with the energy flow analysis.In the model,the combined effect of the acoustic inertance,acoustic compliance,viscous resistance and axial temperature gradient of the regenerators and the turbulence condition of the inertance tube is taken into consideration,which leads to that the theoretical model can describe the realistic situation relative accurately as well as express the analytical relationship among various parameters of the hybrid cryocooler.2)Research the thermodynamic characteristics of Stirling/pulse tube hybrid cryocooler based on the theoretical model,and verify the theoretical model by the comparison with the numerical model.With the help of the theoretical model,the distribution of energy flow and phase difference is analyzed,the thermodynamic characteristics in the hybrid cryocooler is researched and explained from the perspective of the phase distribution.The numerical model of the hybrid cryocooler is established using several thermodynamic design software and the initial value calculated by the theoretical model.Then,the changing situation of the distribution of the gas temperature,wall temperature,acoustic power,phase difference,pressure wave and volume flow with respect to the displacer phase is studied,and the principle of the inter-stage cooling capacity allocation is analyzed.The theoretical model and the numerical model play an important role in the subsequent development of the experimental prototype.3)Design a prototype of Stirling/pulse tube hybrid cryocooler,and verify the theoretical model experimentally.The hybrid cryocooler can obtain 1.16W at 35K plus 7.25W at 85K with 234.6W input electric power and 315K heat rejection temperature,and its relative Carnot efficiency is 12.32%(calculated according to electric power).Meanwhile,it can obtain1W at 30K plus 6.5W at 80K with 262.5W input electric power(including 240W compressor input power and 22.5W displacer input power)and 315K heat rejection temperature,and its relative Carnot efficiency is 10.89%,which reach the demand of the project.The comparison among the experimental results and several high efficient two-stage cryocooler operating at 35K/85K indicates that the cooling efficiency of this hybrid cryocooler has reached the international leading level.The experimental results reveal the phenomenon that Stirling/pulse tube hybrid cryocooler allocates the cooling capacity of both stages by shifting the displacer phase,and verify that there exists a critical phase of the displacer and the inter-stage cooling capacity allocation loses efficacy when the displacer phase exceeds the critical phase.In addition,the cooling performance test experiments are carried out,and the relevant results verify the reliability of the theoretical model.