Frost layer growth behavior study on a cryogenic surface with water vapor content

Abstract

Frosting under cryogenic conditions is common in liquefied natural gas (LNG), cryogenic containers, cryogenic wind tunnels, cryopump and other engineering fields, but the corresponding researches are still insufficient compared with that under general-low temperature conditions. Especially, research on extra-low-content water vapor frosting under cryogenic conditions stays almost blank. A visualization experiment system was built, based on which cryogenic frosting experiments of water-vapor-carrying nitrogen gas flow with different water vapor contents (120 ppmv ≤ ωin ≤ 780 ppmv) considering the cooling process (from 290 K to 100 K) were carried out. Images through the whole frosting period were recorded and image processing was executed. The evolution of the frost surface was captured and the translation velocity was calculated. Physical properties of the frost layer including thickness (as large as 1.75 mm at 2 h) and roughness (up to 76.2 μm) were obtained and compared with humid air frosting. The frost layer growth pattern transition from needle-like vertical growth to clump-grass-like circular rotational growth was observed in the rapid cooling stage. The results reveal differences in frost formation mechanisms and characteristics from general-low to cryogenic temperatures and can provide a quantitative reference for mass and heat transfer analysis in practical frosting circumstances.