Mingyao Xu

Numerical simulation of the second stage regenerator in a 4K GM cryocooler

In a 4K Gifford-McMahon (GM) cryocooler, the performance of the second stage is strongly dependent on the efficiency of the second stage regenerator. In order to improve the efficiency of the second stage regenerator, the internal dynamic parameters are analyzed by numerical simulation. It is found that the performance of a 4K GM cryocooler can be improved by shifting the temperature profile in the second stage regenerator to a higher level. The temperature profile in the second stage regenerator with an artificially reduced heat capacity of the regenerator material at the warm end is analyzed. Based on the simulation results, a novel and simple way, which is to replace the regenerator material at the warm end with a material having a lower heat capacity, is proposed. By reducing the heat capacity to 20 % of lead, the PV power is increased by 7.9 W at the first stage and 1.8 W at the second stage. Correspondingly, the cooling capacity is increased by 9.0 W at the first stage and 0.13 W at the second stage...

Recent development status of compact 2 K GM cryocoolers

To meet the growing demand for a compact cooling solution for superconducting electronic devices, we developed a two-stage 2 K GM cryocooler and a cryostat system, which can reach 46.3 K / 2.2 K on the first and second stages under no-load conditions. Nevertheless, with several innovative technologies applied, the total length of the expander cylinder is reduced to under 70% of the smallest conventional 4 K GM cryocooler. In this paper we will present the design method, including material selection and structure design with detailed explanation, which has been confirmed by both simulation and experiment.

Study of low vibration 4 K pulse tube cryocoolers

Sumitomo Heavy Industries, Ltd. (SHI) has been continuously improving the efficiency and reducing the vibration of a 4 K pulse tube cryocooler. One advantage of a pulse tube cryocooler over a GM cryocooler is low vibration. In order to reduce vibration, both the displacement and the acceleration have to be reduced. The vibration acceleration can be reduced by splitting the valve unit from the cold head. One simple way to reduce vibration displacement is to increase the wall thickness of the tubes on the cylinder. However, heat conduction loss increases while the wall thickness increases. To overcome this dilemma, a novel concept, a tube with non-uniform wall thickness, is proposed. Theoretical analysis of this concept, and the measured vibration results of an SHI lowvibration pulse tube cryocooler, will be introduced in this paper.

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 highefficiency 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 im at the first stage and ±14.6 im 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 sec...