A study of gas spring heat transfer in reciprocating cryogenic machinery

This thesis is a study of the gas spring heat transfer which occurs in reciprocating machinery and the way it affects the performance of these machines particularly cryogenic reciprocators. In this study, a closed volume piston-cylinder apparatus is used to measure gas spring heat transfer under a variety of conditions at room and cryogenic temperatures. Analytic models are developed to represent the gas spring heat transfer and the interaction between the heat transfer and the thermodynamic behavior of the working gas. Pressure and volume waves for a complete cycle from the experiments and analytic models are represented in the form of Fourier series. This way the data are represented by a relatively small number of parameters and without extensive reduction and can be manipulated mathematically with relative ease. We have found that gas spring heat transfer is primarily affected by the piston cycle frequency and the thermal diffusivity of the working gas and that its effects are potentially detrimental for room temperature reciprocators for reciprocators which operate near 77 K, high cycle frequencies would help reduce gas spring heat transfer losses. For temperatures near 10 K, the effects of gas spring heat transfer are small; this is mostly attributed to the extremely large gas densities which occur at these temperatures. Thesis Supervisor: Professor Joseph L. Smith, JR. Title: Professor of Mechanical Engineering