Abstract. The choice of the appropriate installation method plays an important role for accurate temperature measurement. In the cryogenic and high vacuum environment, due to poor contact between the cryogenic temperature sensor and the surroundings that the sensor is installed and intended to measure, the self-heating from sensor measuring current brings about temperature difference and creates a potential temperature measurement error. The self-heating temperature difference is directly proportional to the thermal resistance for a mounted sensor, which means that lower installation thermal resistance of sensors is advantageous to obtain better measurement results. In this paper, a measurement model for the installation thermal resistance of sensor is built in terms of two currents method which is always used to measure self-heating effect. A cryostat that can provide variable temperature in the accurate temperature measurement and control experiments is designed and manufactured. This cryostat can reach 3K in a few hours and the sample temperature can reach as high as 20 K. Based on the experimental results, the measurement uncertainty of the thermal resistance are also analyzed and calculated. To obtain the best measurement results in our cryostat, the thermal resistances of sensors with two installation methods are measured and compared. IntroductionOperation of resistance thermometer requires dissipation of power in the sensor. The heat flux generated by the measurement current creates the temperature difference between the sensor and the environment is intended to measure, which is no doubt to produce temperature measurement error or uncertainty. The self-heating temperature difference relates to the thermal resistance between the sensor and its surroundings. Thermal resistance is a significant factor in temperature measurement uncertainty. How to accurately measure the thermal resistance between the sensor and the environment is an important problem in high precise temperature measurement. Thermal resistance is found to depend on temperature and details of sensor mounting. Apiezon grease and Varnish are always used to mount thermometer sensors in low temperature, because they have high thermal conductivity in low temperature. Details of construction unknown to a user can strongly affect the thermal resistance. It is difficult to calculate an effective thermal resistance for a mounted temperature sensor. Many scholars have done research on the thermal resistances of the cryogenic temperature sensors. Rusby [1] studied the thermal resistances of a standards grade rhodium-iron sensor from 0.4 to 280K; Schoepe [2] calculated the thermal resistances of a thick film resistor from 0.4 to 280K. Thermal resistances were measured at cryogenic temperatures from 1 to 300K on several commercially available temperature sensors by Holmes and Courts [3]. In this paper, the thermal resistances of the Cernox temperature sensor that mounted by two different methods (Apiezon N Grease, VGE-7031 varnish) from 4.2 to 14K are c...

Abstract.A numerical analysis has been carried out on a 16 mm tip diameter radial-axial flow cryogenic turboexpander using He, in order to directly compare performance characteristics by varying the vaneless space. A reference nozzle with radial clearance 0.1 mm was used in the helium liquefaction system, and six other nozzles were designed with radial clearance of 0.3 mm, 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm and 1.5 mm. As part of the design process a series of CFD simulations were carried out in order to guide design iterations towards achieving a matched flow capacity for each design. In this way the variations in the stage efficiency could be attributed to the different vaneless space only, thus allowing direct comparisons to be made. The variation in computed efficiency was used to recommend optimum value of the ratio of the nozzle vane trailing edge radius to the rotor leading edge radius (R te /r le ).