Frost growth behavior on a vertical plate according to airflow direction at ultra-low temperatures

Abstract

Frost formed on equipment operating at ultra-low temperatures (below -100 °C) affects thermal performance and leads to maintenance problems. Despite this need to study frosting behaviors at ultra-low temperatures, studies on vertical plates under forced convection are lacking. In this study, frost growth behavior at ultra-low temperatures on vertical plates was experimentally investigated with buoyancy-assisting and buoyancy-opposing flows under forced convection. Different frost growth behaviors were observed owing to the combined effects of the gravity force of the frost and the drag force exerted on the frost. Specifically, the frost layer formed in the opposing flow had a higher density and lower thickness than that formed in the buoyancy-assisting flow due to the formation of unique frost walls in the opposing flow. The frost wall not only delayed frost growth on the downstream plates but also promoted condensation phenomena in the frost wall. In addition, frosting behavior at ultra-low temperatures on the vertical plate was observed in terms of air velocity (1–3 m/s), air temperature (15–25 ℃), cooling surface temperature (-160 to -100 ℃), and absolute humidity (0.0054–0.0094 kg/kga). Additionally, correlation equations were suggested to predict ultra-low temperature frosting behaviors including average frost thickness and frost density within an error of 10%.