Study On Subcooled Nitrogen Of Heat Transfer And Flow In High Temperature Superconducting Of Cooling System

As the high temperature superconducting (HTS) technology progresses, the critical superconducting temperature rises from the liquid helium temperature to the liquid nitrogen temperature, and the critical current density in liquid nitrogen temperature range has reached the level of practical application. As one focus of the HTS researches, the research of sub-cooled liquid nitrogen in HTS motor has become an important research direction. The thesis researches heat transfer and flow in sub-cooled liquid nitrogen of cooling system in axial-radial flux all HTS low speed synchronous motor, which provides theoretical principle for the design of the motor's cryogenic cooling system.In this thesis, the HTS motor cooling load is calculated based on the structure of HTS motor. For the four-lane paralleled condition, the liquid nitrogen's circulating flow, velocity and the diameter of the pipe are calculated, and the thermal-fluid coupling analysis on the coils and sub-cooled liquid nitrogen of the cooling flow channel is carried out, which obtains the steady temperature distribution. To simplify the structure, the schemes of import and export in the homonymy, and on the different sides are compared, the solution of import and export in the homonymy is adopted finally. Cryogenic heat exchanger is one of the key equipments in sub-cooled liquid nitrogen cryogenic cooling system. Two AL600 cryorefrigerators are used to cool the HTS motor. The heat transfer coefficient is calculated using the theoretical equation,and the liquid nitrogen temperature field in sub-cooled heat exchanger is simulated. The effects of the cool head's height to heat exchange area and extended surface from a cryocooler to the effective heat transfer coefficient and coefficient of overall heat transmission are studied in detail. The simulation result using FLUENT software shows that the velocity value is 1.53m/s-1.54m/s. Temperature reminds unchanged when number of turns is changed but the heat exchange area and height of sub-cooled exchanger is unchanged. Assume the distribution of temperature is uniformity in the fluid reservoir, when the temperature in the fluid reservoir is 64.6K, the temperature of liquid nitrogen in the pipe is below 65K.In the HTS motor's cryogenic cooling system, there is pressure drop when liquid nitrogen flow in the pipe. In order to keep the flow rate steadily, it needs to calculate overall pressure loss to compensate the pressure drop in the pipe. Research on the pressure drop in the siphon pipe, the pressure drop and velocity distributions for different angles(90°,60°,45°, 75°) are simulated, the analysis result shows that when the angles decrease, the pressure drop becomes small, but difference value of it becomes smallbetween two low-angles .