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Description
Free-piston Stirling crycooler, featuring its elimination of the motor that drives the displacer, has extensive applications in various areas for its simplicity in structure and decrease in mass. However, the elimination of the motor has not only added to the complexity of its analysis and design, but also made it differ from Stirling cryocoolers with displacer driving mechanism, such as the integral type and Oxford type, in thermodynamic characteristic. Therefore, an idealized mathematical model has been established and an attempt has been made to analyze the thermodynamic characteristic of free-piston Stirling cryocooler in an analytical approach with this model. To certify the mathematical model, comparison has been made between the results obtained by the model and by a commercial software, which indicates that the two results tend to get closer and closer as more complicating factors are removed from the model in the commercial software. This mathematical model reveals that due to the displacer damping which is necessary to the production of cooling capacity, the COP of free-piston Stirling crycooler base on various idealized assumptions is always lower than that of Stirling cycle, or Carnot cycle. Also, conditions that maximize the cooling capacity are studied in detail with the mathematical model, which reveals the characteristics of an optimized free-piston Stirling crycooler. By excluding all the complicating factors, the idealized mathematical model sheds light on the thermodynamic nature of free-piston Stirling crycooler, and provides an essential reference for its design and optimization.