DEVELOPMENT OF HIGH EFFICIENCY 4 K TWO-STAGE PULSE TUBE CRYOCOOLERS WITH SPLIT VALVE UNIT

SHI has been continuously improving the efficiency and reducing the vibration of a 4 K pulse tube cryocooler. A high-efficiency 4 K pulse tube cryocooler with a split or a remote valve unit has been developed. The valve unit of the cryocooler is split from the cold head by one flexible gas line and two stainless pipes. The experimental data of a high-efficiency pulse tube cryocooler with a split or a remote valve unit is reported in this paper. The diameter of the gas lines between the valve unit and the cold head is optimized. The wall thickness of the tubes on the cylinder is optimized for low vibration with minimum impact on cooling performance. the typical vibration displacement is +/- 10.3 mu m at the first stage and +/- 14.6 mu m at the second stage when the compressor is operated at 50 Hz. When the valve unit is split with 1 m lines, the cooling capacity is reduced because of increased pressure drop and dead volume. The minimum temperature of a prototype unit is 23.0 K at the first stage and 2.30 K at the second stage when the compressor is operated at 50 Hz, and 22.3 K and 2.39 K when the compressor is operated at 60 Hz. A typical cooling capacity of the prototype unit is 35 W at 41.8 K on the first stage and 0.9 W at 4.05 K on the second stage when the compressor is operated at 50 Hz and 35 W at 41.8 K on the first stage and 0.9 W at 4.07 K when the compressor is operated at 60 Hz.