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A double-inlet pulse tube cryocooler, intended for cooling the receivers of a large radio telescope, is currently undergoing testing. The pulse tube and regenerator are arranged in a U-tube configuration, and split from the crank pressure generator currently used, which allows testing at a range of speeds. The bypass results in a substantial performance improvement, and inverting the bypass valve results in noticeable changes, indicating that the valve design is far from symmetrical, hence a nonzero DC flow. An analysis is presented, focusing upon the significant pressure drop in the regenerator, and the relationship between this pressure drop, the associated phase shift, DC flow, and global performance. Finally, results from the analysis are compared with measurements. [ABSTRACT FROM AUTHOR]

Significant pressure drops are typical in the regenerator, and their impact on performance can be significant. It is clear that irreversibilities associated with viscous friction lower efficiency. But in the pulse-tube, this is perhaps not the most crucial issue. Indeed, by virtue of having only one driven element (the compressor), the pulse-tube is a fairly inflexible device from a design standpoint. Pressure and velocity amplitude and phase determine energy fluxes. Impedances depend upon volume distribution, orifice resistances, and viscous friction in the regenerator. While the combined effect of volume distribution and orifice impedance is relatively easy to analyze, the role of the resistance in the regenerator is harder to deal with. An analysis is presented of the regenerator as an arbitrary porous medium, assuming large pressure gradients. Results are readily incorporated within a small amplitude, harmonic, model of the overall device, including the bypass, if any. For simple assumptions with respect to the temperature profile, such as linear and exponential temperature profiles, closed form solutions are obtained. Results from the model are compared with experiments and their relevance is discussed. [ABSTRACT FROM AUTHOR]