Study On Centrifugal Cold Compressor In Subcooled Helium System

In china,subcooled helium is obtained via an oil-ring pump(ORP)at ambient temperature by pumping saturated liquid helium(LHe).However,there are many disadvantages associated with the ORP,e.g.low pressure in the pipes necessitates a stronger vacuum or may result in the contamination of important parts of the cryogenic system.Moreover,ORPs are large in size,require more power and generate a high level of noise.Recently,more subcooled and superfluid systems have been developed based on cold or mixed compression,which rely on cold compressors.However,domestic research in this field is still in the theoretical stage and the subcooled and superfluid helium are obtained via warm compressors at room temperature.To avoid the operational disadvantages associated with ORPs,the centrifugal cold compressor is designed to pump saturated LHe to obtain subcooled helium.Different cold-gas and off-design performances have been investigated via CFD,and a prototype of a cold compressor has been tested using cold nitrogen gas.The main contents are briefly described as follows:First,according to the requirements of the EAST cryogenic system,a centrifugal impeller is designed followed by a motor,heat-insulation structure,diffuser,volute and an inlet pipe.Two of the most crucial points in the cold compressor are the heat-insulation structure and seal structure.The heat-insulation material is selected,and the dimensions of the thermal anchor are deternined based on a theoretical analysis.Moreover,the effects of these design parameters on the cold compressor's performance are considered.Finally,four types of seal structures are tested at the temperature of liquid nitrogen(LN2).Next,the impeller is designed by calculating the performance parameters based on the geometric parameters.The effects of speed and mass flow rate on the cold compressor at the temperatures of LHe and LN2 temperature are investigated theoretically,and the surge line is predicted.Then,the effects speed and mass flow rate on the cold compressor at the temperatures of LHe and LN2 were investigated using a Workbench numerical simulation.To obtain a high efficiency and expand the range of stable operation,the parameters of the impeller are optimized;these parameters include the blade wrap angle,b2/D2,stagger angle,outlet angle and number of blades.Moreover,various performance parameters of the impeller are considered,including the natural frequency of the vibration of the impeller and the axial's vibration,using a SolidWorks simulation.Finally,the cold compressor is tested at room temperature and the temperature of LN2.The heat leakage,surge line,pressure ratio curve,efficiency curve and tip clearance are measured at the temperature of LN2,and the values are compared to those obtained via theoretical calculations and numerical simulation.