Flow And Heat Transfer Of Liquid Nitrogen In Corrugated Tubes And Capillary Tubes

With the development of the superconductor technology, high temperature superconducting (HTS) cable has been developed. However, the hydraulic characteristics in the HTS cable must be well investigated to design the transmission line.Especially the pressure drop in the transmission line is an important parameter to design, because the pressure drop decides the length of the transmission line and the pump power. The corrugated tube is used in the HTS power because of its flexility and contractibility. However the friction factor in corrugated tubes has been not well studied. So it is important to study the flow characteristics in corrugated tubes. They are investigated systematically in the paper.Experiments have been conducted to study the pressure drop characteristics of liquid nitrogen, nitrogen gas and water in three corrugated tubes with the diameters of 6mm, 8 and 10mm. The friction factors are compared with the conventional correlations over a Reynolds numbers of 4000-40000. The pressure drop increases with the mass flux increases. The pressure drop increases with the Reynolds numbers increase. The friction factors of the corrugated tubes are higher than those of the smooth tubes. The corrugation geometries have big influences on the flow. The friction factor decreases with the depth of corrugation decreases. mmWe make comparison between liquid nitrogen, nitrogen gas and water flow characteristics in corrugated tubes. And find that the pressure drop of liquid nitrogen is between water and the nitrogen gas at the same Reynolds numbers. While the friction factor of water is smaller than the nitrogen gas at the same Reynolds numbers. The thermo-physical properties have big influences on the flow.The detailed flow characteristics of the liquid nitrogen in corrugated tubes are investigated by numerical simulation for different inlet fluid velocities and tube geometries, i.e. different sizes of the pitch and depth of corrugation. The pressure and velocity field contour plots are obtained and analyzed. The pressure drop increases with the velocity increases. The results of friction factor show that the influences of pitch and corrugation depth are significant but the dependency on the Reynolds number is not severe. The friction factor decreases while the s/t increases.Liquid nitrogen is the most competitive potential substance for cooling superconductor. Superconductor may be any shape, including thin wire.Capillary tube is a compact choice when designing superconducting thin wire cooler.Natural convection in liquid nitrogen around a thin wire heater placed in the center of the capillary is numerically studied. We mainly discuss the effect of the diameter sizes and the inclination angles of the capillary tubes on the heat transfer performance. The inclination angles of the capillary tubes are 0°, 30°, 60°and 90°with the diameters of 1.2 and 2.0 . The numerical simulations are performed with the software-FLUENT. The typical distribution of the velocity and temperature of the liquid nitrogen in the capillary tubes is obtained. The results show that the heat transfer performance is better when the inclination angles are 30°and 60°and the heat transfer performance in the 2.0 diameter capillary tube is also better than that in 1.2 diameter capillary tube.