Cooldown Temperatures and Cooldown Time during Mist Flow

Abstract

In recent years, cryogenic fluids have found wide applications as coolants as well as propellants in rocket propulsion. During transient operation of such systems, the transfer lines or flow passages must be cooled down to the liquid boiling point before the maximum flow rate is attained. In order to design coolant channels and transfer lines, the duration of the cooldown period must be known. Consequently, a number of cooldown studies have been carried out. Burke et al. [1] studied the cooldown of a 175-ft, 2-in.-OD stainless steel line by liquid nitrogen, and Bronson et al. [2] studied the cooldown of a 50-ft, 13/8-in.-ID test section by liquid hydrogen. The former investigator used a gross effect to calculate cooldown time. In this method, an average exit exhaust temperature was used. Bronson et al. [2] assumed a constant wall-to-coolant temperature difference along the entire length of the line. Although these techniques may provide sufficient accuracy when the gross effect over an extremely long transfer line is considered, it is doubtful that they can be applied over a short tube. In addition, these methods do not permit the estimation of instantaneous wall and bulk fluid temperatures.