Effect of Pressure Wave Form on Pulse Tube Refrigerator Performance

Abstract

We have constructed a pulse tube refrigerator (PTR) test apparatus that can be operated in different modes: as basic, orifice-, or double-inlet-type PTR. A special motor driven multi channel rotary valve in combination with needle valves serves to control the Helium gas flow between compressor and refrigerator inlets. With dynamic pressure and temperature sensors at various positions and a calibrated heat input at the cold end the cooling performance of the refrigerator was studied systematically under various working conditions, such as frequency and amplitude of the pressure wave and the settings of the orifice and second inlet flow. Keeping constant the average mass flow through the rotary valve, particular attention has been directed towards a possible effect of the shape of the pressure wave. A minimum temperature of 42 K has thus far been achieved with double inlet configuration using a frequency of 2.1 Hz, an average pressure of 21 bar, a high to low pressure ratio of 1.32, an average mass flow rate through the rotary valve of 1.0 g/s, and an approximately trapezoidal wave form. Under these conditions, the net cooling power at 80 K is Q = 2.5 W. With a higher pressure ratio of 1.5, corresponding to an average mass flow of 1.56 g/s, Q = 4 W at 80 K is obtained at the expense of a higher no-load temperature of 52 K. In all three modes of operation the net cooling power varies linearly with cold end temperature. For orifice and double-inlet configuration the measured slopes dQ/dT are in qualitative agreement with the enthalpy flow theory of Radebaugh et al.. A significant effect of the pressure wave form on the minimum temperature and the temperature profile along the pulse tube has been observed. While holding all other parameters constant, the minimum temperature increases markedly when the dwell times at high or low pressure are reduced. Regarding high cooling power, the optimum wave form is characterized by a long dwell time at high pressure, which may be ascribed to an increased heat transfer to the hot heat exchanger.