Study on the frost formation, heat and mass transfer on the cryogenic surface during cooling and filling process

Abstract

The heat and mass transfer on the cryogenic surface during the cooling and filling process under natural convection was experimentally and numerically investigated. The experimental study showed that the cooling process had a strong effect on heat and mass transfer on the cryogenic surface. The frost formed on the cryogenic surface with the cooling and filling process is very stable and had fine structure. But the frost formed on the cryogenic surface without the cooling process was unstable and had sparse structure. The frost under the cooling and filling process grew considerably thicker than that without the cooling process. The maximum heat flux and minimum heat flux under the cooling and filling process was about half of that without the cooling process. This trend was also confirmed by the boil off test performed on the entire test section. Therefore, the heat flux at the cryogenic constant wall surface temperature condition, which prohibit the growth of frost during the cooling process, overestimated the incoming heat flux compared with the heat flux during the cooling and filling process like the rocket pre-launch operation process. In addition, a modified frost growth model was proposed by reflecting transient wall temperature to predict heat and mass transfer characteristics during the cooling and filling process. And the new correlations for the frost density and combined model for the frost thermal conductivity were suggested. In order to validate the proposed numerical model, experiments were performed under various ambient air temperature and relative humidity conditions: $10\circ C \leq Ta \leq 30\circ C$ and $30% \leq RH \leq 90%$. The maximum and minimum heat flux from the numerical model showed a good agreement with experimental data within 10% and 16% average relative error, respectively. The final frost thickness from the numerical model showed good agreement with experimental data within 13% average relative error except for one case where mass transfer was reduced due to local frost collapse and fog formation near the cryogenic surface. Sensitivity analysis was performed for the parameters of proposed numerical model and the effects of main parameters on the frost thickness and wall heat flux were analyzed. Therefore, the numerical model will be useful for estimating the heat transfer rate in an uninsulated cryogenic system, such as a rocket oxygen tank.