Numerical Analysis of Forced Convection Heat Transfer of Subcooled Liquid Nitrogen

The knowledge of forced flow heat transfer of liquid nitrogen and liquid hydrogen is important for cooling design of large scale HTS superconducting magnets wound with YBCO, BSCCO or MgB₂ conductor adopting indirect cooling or inner conductor cooling, such as CICC configuration. As a first step of the study, forced flow heat transfer of liquid nitrogen in a horizontal tube was analyzed in this work by using a CFD code. The use of a CFD code is necessary to understand the influence of a configuration and a direction dependency of a cooling channel on the local heat transport phenomena in the practical cooling channel of the magnet. The solutions obtained by using the low Reynolds number kappa-epsiv model as a turbulent model agreed with the authors´ experimental data and with the values predicted by the Dittus-Boelter (D-B) correlation for the Reynolds numbers (Re) higher than 1 times 10⁴.For Re < 1 times 10⁴, the solutions tend to approach the solutions for the laminar flow. Local heat transfer at circumferential and longitudinal positions in the horizontal tube was analyzed for various flow velocities. Large circumferential and longitudinal temperature distributions were observed in the solutions for Re < 1 times 10⁴. Local temperature change of a magnet in a cooling channel which cannot be evaluated by using the conventional heat transfer correlation such as D-B correlation should be considered for the cooling design of the large scale forced flow cooling HTS magnets.