Frosting phenomenon is widely seen in nature and also observed in space station. To deeply understand the gravity effect on frosting characteristics, and thus accurately predict and control the frosting process in space station, series of frosting experiments were designed and conducted on cold surface with three different placement angles at surface temperatures of −25 °C and −15 °C under natural convection. The results show that gravity primarily affects the frosting characteristics by changing the flow field of water vapor and the heat transfer capability near the frost layer surface. As cold surface placement moves from horizontal to vertical to inverted, the peak value of average frost layer thickness during the early stage increases to 206.43 × 10−6 m and 297.14 × 10−6 m, and the peak frosting rate is reduced to 4.98 × 10−6 m/s and 3.47 × 10−6 m/s throughout the whole frosting process, respectively. With the changing of cold surface placement, the time when the first reverse melting occurs on the frost layer surface was extended by 121.53 % and 57.37 %, the frequency of reverse melting was reduced by 30 % and 40 %, and the maximum value of reverse melting was reduced by 79.53 % and 91.09 %, respectively. This study could serve as a reference for frosting models, or development of anti-frosting or defrosting technologies in space station.
