Experimental Investigation on No-Vent Fill process using Tetrafluoromethane (CF4)

Abstract

No-vent filling (NVF) method is a cryogenic fluid transfer technology and one of the most promising techniques for a long-term space mission. It saves the amount of cryogenic propellant and eliminates of a venting process which causes unintended momentum change on a space vehicle. In order to demonstrate a successful NVF process including no-vent pre-chill down process, we prepared an experimental apparatus consisting of a cryogenic storage tank, a transfer line and a receiver tank which is conductively cooled by a precooler. A stirling cryocooler (CryoTel® GT, Sunpower) is utilized for thermal conditioning of the receiver tank around the saturation temperature of CF4 and to achieve a cryogen-free pre-chill down process. Vacuum condition of the experimental apparatus is maintained below 〖10〗^(-3) torr to minimize heat leak and to simulate space condition. Tetrafluoromethane (CF4) is selected as a working fluid due to the similarity in a molecular structure with Methane (CH4), which has been considered as an attractive future cryogenic propellant, and the safety. Liquid CF4 is obtained by heat exchange with liquid nitrogen in the supply tank. The initial wall temperature of the receiver tank is pre-regulated by the cryocooler to identify its impact to NVF. The flow transfer conditions (the mass flow rate, the pressure and the temperature) of the working fluid are also varied with care to investigate the experimental parameters of NVF process. NVF process is achieved without losing any transfer fluid even in the pre-chill down process. An equilibrium NVF model is developed to find an optimum condition of the required filling volume and is validated with the experimental results. We also perform other parametric studies to investigate the critical influencing factors for NVF.