Kouki Naka

Thermofluid Analysis of Shuttle Loss on Regenerative Cryocoolers

Shuttle loss is one of major losses of regenerative cryocoolers. In order to improve the efficiency of the cryocoolers, we have to estimate the shuttle loss precisely and reduce it. However, it has been difficult to calculate shuttle loss precisely because the hydrodynamic behavior of the working fluid has not been considered in the analyses and the temperature gradient of the working fluid was given as linear. Therefore, using a general purpose thermofluid analysis software STAR-CD1, we made a model in which the hydrodynamic behavior of the working fluid was considered. By using this model we did a thermofluid analysis which calculated the movement of the working fluid and the temperature change. From this, we calculated the shuttle loss. As a result of these calculations, the preciseness of the calculation model was confirmed by comparing with previous analyses. This means that acceptable analysis is possible with general purpose software, and various models. This paper reports on the analysis model and the results.

Effects of Thermal Conductance in the Cooling Stage of a 4K-GM Refrigerator on Refrigeration Capacity

This paper describes the effects of thermal conductance in the cooling stage of a 4K-GM refrigerator on its refrigeration capacity. Calculation of the temperature difference between the gas and cooling stage in the expansion space of a 4K-GM refrigerator has shown that the thermal conductance between the gas and cooling stage is inadequate, and the heat transfer loss is too large to be ignored. Hence, we have made improvements in the shape and material of the cooling stage to increase thermal conductance, and have been successful in increasing refrigeration capacity at 4.2 K from 2.2 W to 3.0 W.