The Role of the Orifice and the Secondary Bypass in a Miniature Pulse Tube Cryocooler

Abstract

This paper focuses on the phase shifting role of the orifice and the secondary bypass in a miniature pulse tube cryocooler. Firstly, the equation of the mass flow rate through the valve is extended into the Fourier series to investigate the phase difference between dynamic pressure in the pulse tube and mass flow rate at the hot end of the pulse tube. The analytical results show that the orifice opening has weak effect on the phase difference between the pressure and the mass flow rate at hot end when the secondary bypass is closed. And the mass flow rate at the hot end of the pulse tube is almost in phase with the dynamic pressure in the pulse tube. The introduction of the secondary bypass will make the pressure in the pulse tube always lead the mass flow rate at the hot end. For the orifice pulse tube cryocooler, the experiments show that with the orifice opening increasing, the phase difference is increasing but less than 3 degree for the opening of the orifice within the range from 0.2 to 2 turns. Based on the optimum orifice opening, the phase difference between the pressure in the pulse tube and the mass flow rate at the hot end increases as the opening of the secondary bypass increases. The experimental result agrees with the analytical result qualitatively.