Experimental Investigation of Cryogenic Line Chill-down Technology by Liquid Nitrogen

Abstract

Cryogenic propellants must be fed into rocket engines steadily in a subcooled state to avoid cavitation phenomena; therefore, the line chill-down process is significantly important in the cryogenic operation of space vehicles. Generally, some portion of the initially transported cryogenic liquids are used as the coolant to chill down the transfer line. Minimizing the line chill-down time and the consumption of the cryogenic propellant during the line chill-down is the main issue. In this study, the cryogenic line chill-down experiments are conducted on a 12.7 mm outer diameter, 1.25 mm wall thickness and 7 m long stainless steel horizontal pipe with liquid nitrogen (LN2). The pipe is vacuum jacketed to reduce heat inleak from room temperature environment to the cryogenic liquid. The temperature and the pressure profiles of the chill-down line are obtained at the location 6 meters away from the pipe inlet under various mass flow rates. The history of the transient temperature, the pressure and the mass flow rate are analyzed and presented for one representative pipe line geometry.