Abstract
Abstract CFD models are used to study the performance of circular and annular pulse tubes working at 77â300 K. The oscillating flow and heat transfer characteristics are investigated. In terms of pulse tube impedance, simulation results indicate that the annular shape has negligible influence when the length and flow area are kept the same as circular pulse tube. However, compared with the circular pulse tube, the thermal performance of annular pulse tube apparently deteriorates which is mainly due to the increased thermal losses caused by heat transfer between the internal gas and two cylindrical tube walls (instead of one in the case of circular pulse tube). The expansion efficiency (defined as the enthalpy flow divided by acoustic power at the cold end) of annular pulse tube is lower by about 14% compared with that of circular pulse tube. Among the influencing factors, hydraulic diameter of annular pulse tube has a significant influence on the performance, and smaller hydraulic diameter leads to a reduced expansion efficiency. The effects of tube wall thermal conductivity are also discussed. This study provides a better understanding on the mechanism of annular pulse tube which sets the basis for optimizing a compact low temperature cryocooler for future applications.
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