Cryogenic Transfer Line Chilldown

Abstract

The transient behavior of a small‐scale cryogenic transfer line was investigated during chilldown to cryogenic temperatures. The vacuum‐jacketed apparatus consisted of a vertical tube followed by a near‐horizontal tube. The tube diameter was 1 cm and the overall length was 4.4 m. The apparatus was equipped with view‐ports in the near‐horizontal section to allow visual observation of the flow patterns. Wall temperatures were measured at various locations along the length of the transfer line. Each test was conducted at a constant liquid volumetric flowrate at the transfer line inlet until saturation temperatures were obtained throughout the system. Liquid flowrate was varied by more than two orders of magnitude and resulted in chilldown times ranging from a few minutes to several hours. An optimum flowrate exists that minimizes liquid consumption during the chilldown process. At higher flowrates, there is insufficient time for heat transfer from the liquid to the wall and inefficiencies result from the greater amount of incompletely vaporized liquid passing through the system. At lower flowrates, chilldown time and total ambient heat leak into the system increase, which raises liquid consumption. The experimental values of liquid consumption are compared to analytical estimates. At low flowrates, the data compares favorably to a minimum consumption model while at high flowrates the maximum consumption model overpredicts hydrogen consumption and underpredicts nitrogen consumption.