Investigation about basic heat transfer law in the micro pulse tube

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Pulse tube is one of the main parts of the pulse tube cryocooler. Ideally, the pulse tube works under adiabatic environment without heat transfer loss. But in real case, entropy is generated in the pulse tube itself from heat exchanged with the walls, turbulent mixing of the hot and cold gas segments, circulation of the gas within the tube, and end effect losses from the adiabatic to isothermal transition in the cycle. All these processes reduce the enthalpy flow in the pulse tube from the ideal acoustic power. However, no 1D model can sufficiently simulate these effects in the past. Also, most of the 1D models about the pulse tube part with a heat transfer coefficient is far from accurate, especially for micro pulse tube in which the heat transfer is more obvious. This work revealed that the basic heat transfer changes instantaneously and shows different tendencies in different time of one cycle, and no suitable law or explanation could fare well the phenomenon eventually. The phase angle changes from negative to positive that results in the relatively heat flux along the pulse tube becomes smaller, that could help the pulse tube to make a good performance.