Home > Proceedings of the 14th International Cryocooler Conference > Spoor

Abstract

One of the chief advantages of Joule-Thomson or GiffordMcMahon cooling systems over the more recently developed acoustic Stirling variety (e.g. high-frequency “pulse-tube� coolers) is the large separation distance between the compressor and coldhead. Long, flexible transfer lines typically connect the two components. This permits insertion of the coldhead into locations where the complete system would never fit, and isolates the coldhead from the vibrations of the compressor. High-frequency “split� Stirling and acoustic Stirling systems are not uncommon, but the separation distance is usually quite small, with a significant penalty on system efficiency. The usual approach has been to minimize the “dead volume� in the transfer line, making it relatively short and very small diameter. Recently, we have explored a different approach, using a fairly large transfer line diameter to lower the flow velocity (and hence the viscous loss), and increasing the length to over 1meter, to allow these coolers to be used in the same applications as J-Ts and GMs. For small systems, this means using slightly larger compressor pistons to create the extra volume flow. The increase in compressor power required is small, because while there are losses in the transfer line, a long transfer line acts like an acoustic transformer, lowering the dynamic pressure at the compressor pistons for a given dynamic pressure at the coldhead. This lowers the seal loss in the compressor, which at least partially cancels the losses in the transfer line. In large systems, the increase in power is proportionally less, because the surface-to-volume ratio of the transfer lines is lower, and seal loss is a bigger fraction of the total input power. We will present simulations for various size systems, and data for one or two prototype systems, comparing capacity and efficiency with and without a long transfer line.