Development of a tube-in-tube heat exchanger for a cryocooler based helium recondensation system

This paper reports design, fabrication and testing of one of the recuperative heat exchangers for a small capacity helium recondensation system. A tube in tube heat exchanger, with multiple tubes in a coiled outer tube, has been designed to operate in the 300 K-100 K range. The key parameters of the heat exchanger are optimized by numerical analysis to obtain highest heat transfer coefficients and lowest pressure drops to meet the design goals. The pressure drop performance of the heat exchanger was tested and it is found that the annular pressure drop increases due to spacer string beyond the design toleration. Pressure drop was also measured after removing the spacer string and the results agree with the correlations available in literature. Spacer pressure drop should be considered in heat exchanger design.