Comparative Numerical Study of Pulse Tube Refrigerators

The focus of this work is the modeling and performance comparison of different models of pulse tube refrigerators, namely, the Orifice Pulse Tube Refrigerator (OPTR) and the Inertancetube Pulse Tube Refrigerator (IPTR) with both in-line as well as coaxial configurations. A detailed analysis of the flow and heat transfer in various components of the above mentioned models under oscillating flow conditions is carried out using FLUENT. Parametric studies are also performed with different length-to-diameter ratios of the IPTR in-line design, in order to determine the optimum geometry for attaining the lowest temperature in the cold heat exchanger under no-load condition. The components of the OPTR are the compressor, transfer line, after cooler, regenerator, cold heat exchanger, pulse tube, hot heat exchanger, orifice valve (usually a needle valve to control the mass flow rate) and the buffer. The modeling of IPTR requires the modeling of inertance tube (a long narrow tube) instead of orifice. The mathematical model consists of the full set of compressible conservation equations with the assumption of axi-symmetry. The regenerator and other heat exchangers are modeled using porous approximation both with thermal equilibrium and thermal non-equilibrium assumption. The effect of axial conduction on performance of pulse tube refrigerator is also analyzed by introducing the wall thickness. The results show that the no-load temperature reached in the cold heat exchanger of IPTR in-line configuration is lower compared to other models. It can also be seen that the interaction of the pulse tube wall and the oscillating flow is an important factor, and that the simplified models tend to over-predict the cold heat exchanger temperature. The thermal non-equilibrium analysis yields a lower cold heat exchanger temperature.