ABSTRACT
The time constant may also be decreased by increasing the convective heat transfer coefficient at the surface of the system. The cooldown times in the problem are somewhat long, because the convection heat transfer coefficient is relatively small. The heat transfer coefficient between the sphere and the fluid is due to natural convection. One thermal problem in cryogenic systems is the need to cool a mass rapidly and effectively from ambient temperature to the operating temperature of the cryogenic system. Valves, joints, and other components in a cryogenic fluid transfer system must be cooled before effective fluid transfer can take place. The cooldown times in this problem are somewhat long, because the convection heat transfer coefficient is relatively small. In the process of deep cryogenic treatment of metal parts, cold gaseous nitrogen is passed over the surface and the temperature of the nitrogen coolant is decreased at a controlled rate.
