Liang Jingtao

Research of pulse tube refrigerator with high and low temperature double-inlet

Through analyzing phase relation between pressures and flow characteristics of double-inlet and multi-bypass, mechanism of double-inlet to lower the temperature of pulse tube refrigerator is proposed. Then another proposal is put forward to replace the low temperature multi-bypass valve, which is another double-inlet valve at room temperature and a small tube prolonging to the low temperature part of pulse tube. Through experiment, this multi-double-inlet version proves effective to lower the refrigeration temperature. Test acquires a lowest temperature of 37 K with two double inlet valves and 50 K with one double inlet valve. The concept of low temperature double-inlet is proposed here for the first time.

Analytical study of the performance of pulse tube refrigerator with symmetry-nozzle

This paper analyzes the mechanism of the symmetry-nozzle instead of needle valve or orifice to improve the performance of pulse tube refrigerator in experiments. Their identifications are to result in a similar reciprocal movement in the hot end of the pulse tube; their differences are that their flow coefficients have different characteristics. The flow coefficient of the symmetry-nozzle has a positive feedback to flow rate while the orifice has little relation to flow rate generally. Further analysis shows that this feature results in large refrigeration when the pressure ratio and mass flow amount are same, which explains the reason for even lower temperature and a larger refrigeration amount when using the symmetry-nozzle.

Optimization of the tube in tube counter-flow heat exchanger in a 4.5 K hybrid J-T cryocooler to be used in space

Hybrid J-T cryocooler is commonly employed in space detective missions requiring liquid helium temperature. In fact, nearly all the space applications of mechanical cryocoolers working at 4.5 K, having been launched or under development are hybrid J-T cryocoolers. For instance, mechanical cryocoolers used in Planck, JWST, SMILES, SPICA and so on, are all J-T cryocoolers precooled by adsorption cryocooler, Stirling cooler or pulse tube cooler. But there is hard any research on space hybrid 4.5 K J-T cryocooler in China. Key Laboratory of Space Energy Conversion Technologies in Technical Institute of Physics and Chemistry has developed a 4.5 K J-T cooler precooled by three stages of pulse tube cryocooler. Base on this cryocooler, design optimization is carried out on the tube-in-tube counter flow heat exchanger to improve its performance. Counter flow heat exchanger is one of the key components of the 4.5 K hybrid J-T cryocooler. Spiral tube-in-tube heat exchanger is widely used in 4 K class hybrid J-T cryocooler because of its advantages of light weight and small size. The impact of tube-in-tube heat exchanger on J-T cycle is analyzed. And J-T cycle is able to provide more cooling capacity and needs less precooling power as the efficiency of the counter flow heat exchanger increases. Then, for the purpose of improving heat transfer efficiency of the counter flow heat exchanger, design optimization is carried out on the basis of theoretical analysis. The main heat transfer resistance of the counter flow heat exchanger is the convection heat transfer between return gas and the outer wall of inner tube. Thus, smaller tube is used to decrease the main heat transfer resistance. Besides, the centrifugal force of the moving helium flow in the spiral pipe brings about secondary flow. The development of secondary flow results in enhancement of heat transfer of the counter-flow heat exchanger. So heat transfer coefficient of the heat exchanger increases with decreasing diameters of the tubes and the spiral diameter. On the other hand, when the efficiency of the counter flow heat exchanger rises, the high pressure flow will be precooled much more fully, which means less precooling power from the precooling cooler will be consumed. As a result, the power consumption of the whole hybrid J-T cooler will decrease and its efficiency will be improved. Then, experimental research is conducted and the experimental results agree well with theoretical analysis. The temperature before throttling decreases as the efficiency of the counter flow heat exchanger increases. At the same time, the cooling capacity increases while the precooling power decreases. However, the cooling capacity and precooling power are smaller than theoretical analysis which attributes to the mass flow rate of calculation is much larger than measured one. Consequently, the benefit of improving heat transfer efficiency is verified. As the efficiency of the counter-flow heat exchanger increases, the cooling capacity of the J-T cooler is improved while the precooling power is cut down. Eventually, the cooling capacity of the hybrid J-T refrigerator at 4.7 K is improved from 15 to 32 mW.