The effect of initial wall cooling from ambient temperature to cryogenic temperature on heat and mass transfer at the cryogenic surface under natural convection was experimentally and numerically investigated. The experimental study showed that the initial wall cooling had a strong effect on heat and mass transfer at the cryogenic surface. The frost under initial wall cooling grew considerably thicker than the case without initial wall cooling. The maximum heat flux under initial wall cooling was 40% of that without initial wall cooling, and the minimum heat flux under the initial wall cooling was 52% of that without initial wall cooling. In addition, a numerical model for the frost formation accounting for initial wall cooling was proposed. The proposed numerical model could explain the heat and mass transfer at the cryogenic surface during the cooling process as well as the filling and holdup process. In order to validate the proposed numerical model, experiments were performed under various ambient air temperature and relative humidity conditions: 10 degrees C <= Ta <= 30 degrees C and 30% <= RH <= 90%. The maximum and minimum heat flux from the numerical model showed good agreement with experimental data within 10% and 25% error, respectively. The final frost thickness from the numerical model showed good agreement with experimental data within 13% error except for one case where mass transfer was reduced due to fog formation near the cryogenic surface. Therefore, the numerical model will be useful for estimating the heat flux in an uninsulated cryogenic system, such as a rocket oxygen tank. (C) 2017 Elsevier Ltd. All rights reserved.