Speaker
Description
Abstract: Pulse tube (PT) cryocoolers are versatile systems which can be used, among other applications, for cooling sensors down to very low temperatures in order to increase their sensitivity through the strong reduction of the thermal background noise of measurements. Therefore, PT cryocoolers must be miniaturized and operate without bringing vibrations into the total system. Thus, the mechanical pump usually used in these systems as the compressor stage, could be replaced by a Knudsen pump whose principle is based on the thermal transpiration obtained by applying exclusively a tangential temperature gradient along a surface, without the action of any moving part or external pressure gradient. However, as rarefaction conditions are needed in the gas flow for the thermal transpiration effect to be efficient, limited pressure levels can be obtained at the pump outlet.
To develop such a PT cryocooler, numerical studies have shown their importance in predicting the influential parameters on flow inside the pulse tube. The main objective of this work is thus to use CFD methods to examine the cooling performance at low charging pressure and optimize the design parameters of miniaturized PT cryocoolers. The operating pressure has been set to 2 bar with a pressure amplitude ranging between 1 and 2 bar. The numerical studies were performed using two-dimensional axisymmetric analysis of an inertance pulse tube cryocooler (IPTCC) with the help of the commercial CFD tool ANSYS FLUENT. As a fundamental case, the geometrical set-up investigated by [1] is considered. After achieving periodic steady state, numerical results have been compared. The numerical studies at low pressure have shown that cooling performance can be improved by increasing the pressure ratio. In addition, it was demonstrated that the recirculation flow pattern observed near the cold end of the pulse tube was due to the scaling down of individual part components of the IPTCC, their aspect ratio (length to diameter ratio) being kept similar. This recirculation zone increases the flow velocity near the cold end and reduces the cooling performance. In this study, the design parameters (such as inner diameter, length) of part components have been carefully modified to develop uniform flow with the aim to improve the cooling efficiency of the device.
References:
[1] T.R. Ashwin, G.S.V.L. Narasimham, and Subhash Jacob. CFD analysis of high frequency miniature pulse tube refrigerators for space applications with thermal non-equilibrium model. Applied Thermal Engineering, 30(2):152–166, 2010
| Submitters Country | Germany |
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