Frost growth characteristics on vertical plates at ultra-low temperatures: frost separation phenomenon and surface treatment

Abstract

Frequent frost separation during frosting has been reported for vertical plates at ultra-low temperatures; however, the mechanism and effects of these phenomena on frost growth remained unclear. In this study, frost separation during frosting was experimentally characterized on vertical plates at ultra-low temperatures (-180 °C to −100 °C) for natural convection and forced convection. Frost separation during frosting was prominent at surface temperatures of < -120 °C and < -170 °C in natural and forced convection, respectively. Frost separation was observed more frequently on the lower cooling surfaces. In these ultra-low temperature regimes, flake-type frost separation was observed in the early frosting stage, which subsequently evolved into lump-type frost separation in the late frosting stage. Frost separation during frosting decreased the average frost thickness and recovered the heat flux of cooling plate. Frequent frost separation was attributed to the combined effects of low frost density and the weak adhesion of ice particles to cooling surfaces. To verify this, the frost separation phenomenon was further compared on vertical plates of bare and superhydrophobic surfaces at ultra-low temperatures. The results showed that the low adhesion of superhydrophobic surfaces accelerated frost separation during frosting.