Measurements of Thermal Performance of the Regenerator of a Cryocooler with a high Number of Transfer Units Value

Abstract

Hundreds of stacked wire screens are used in the regenerator matrix of a common cryocooler. The number of transfer units of such a matrix (denoted as NTU_m) may well exceed 60. However, most of the earlier studies reported are limited to studies of regenerators with NTU_m values less than 60, as the single-blow method was employed to measure the NTU_m value of the regenerator matrix. Furthermore, in these earlier studies, the effect of heat transfer from the working fluid to the external tube and the Joule-Thomson effect were neglected.

In the present study, three regenerators having high NTU_m values have been constructed and a transient single-blow technique has been employed to measure the friction factor and the heat transfer performance of these regenerators. In addition, an improved model has been adopted to correct the shortcomings of the earlier studies.

Empirical correlations have been provided for the relation between the friction factor and Reynolds number and between the Nusselt number and Reynolds number. The correlation with smaller NTU_m values agreed well with those reported in earlier studies.

Keywords

heat transfer measurement cryocooler regenerator

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