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In this paper, a type of mutual inductance sensor based on the PCB technology is proposed for cryogenic radial displacement measurement. Firstly, the feasibility of the scheme is analyzed from the aspects of the low temperature usability of materials and components, and the temperature sensitivity of the sensor. Then the experiments at low temperature (77 K) and room temperature are carried out with a simple and effective setup. The experimental results show that the sensitivity has no obvious change from room temperature to low temperature, and the linearity remains at a good level. However, the standard deviation and repeatability of the measurement are affected by external factors. Generally speaking, this paper verifies the feasibility of applying this sensor to micro displacement measurement at low temperature, which lays a foundation for the development of more mature displacement sensor for HTS bearing.

Cold compressors are the core components needed for the development of a facility for large-capacity refrigeration at superfluid helium temperature. The compressor impeller operates at extremely low temperature and low pressure which involves a performance penalty due to heat transfer from the warm side of the machine to the cold side and thus affects the recycle of the cold exergy downstream. To investigate the heat transfer effect on cold compressor performance, a conjugate heat transfer analysis is performed with commercial CFD solver and is then validated with the experimental data tested at different rotation speed. Then a series of configurations of different thermal boundaries are analyzed to investigate the influence of heat transfer on performance. The simulated results show that the external heat transfer has a negative impact on pressure distribution. The helium gas inside the impeller flow domain is more sensitive to external heat leakage comparing with that inside the diffuser flow. More than that, the mass flow leakage through blade tip clearance is highly affected by the external heat transfer, which counts for the performance degradation.

The purpose of this paper is to investigate the stability of oscillation modes in a thermoacoustic Stirling prime mover, which is a combination of looped tube and resonator. Two modes, with oscillation frequencies of 76 and 528 Hz, have been observed, stabilities of which are widely different. The stability of the high frequency mode (HFM) is affected by low frequency mode (LFM) strongly. Once the LFM is excited when the HFM is present, the HFM will be gradually slaved and suppressed by the LFM. The details of the transition from HFM to LFM have been described. The two stability curves of the two modes have been measured. Mean pressure Pm is an important control parameter influencing the mode stability in the tested system.

The work proposes a simple and feasible calculation method––network model method to calculate temperature differences generated in thermo-driven thermoacoustic refrigerator (TAR). The theoretical calculation model is first built. The network model is given and used to make numerical calculations under different conditions including heat-pump stack positions in TAR, different oscillating pressure ratios (PR), plate spacings and different stack geometries. Theoretically calculated results show that the former two factors make significant influence on temperature differences, the influence of stack spacing on temperature difference has relation with PR, and cooling effect of pin-array stack is superior to that of parallel plate stack under other same conditions. Furthermore, theoretically calculated results and experimentally measured data are in good agreement at small acoustic pressure amplitude.