Frost layer growth behavior under cryogenic conditions

Highlights: • Frost growth behavior was experimentally investigated under the cryogenic conditions. • Shrub-shaped frost crystals appeared due to the unique frosting mechanism. • The frost thickness decreased as the cooling surface temperature decreased. • The increase in the air velocity increased the frost thickness. -- Abstract: This study aims to achieve an in-depth understanding of frost layer growth behavior on cryogenic surfaces (below −100 °C) under forced convection conditions. Carrying out frosting experiments using liquid nitrogen led to observations of the characteristic phenomenon in the frost layer growth behavior. Particularly, frost layers were growing separately in the leading edge and downstream of the cooling surface under the unique frosting mechanism. Irregularly sized shrub-shaped frost crystals, which were not observed in the previous studies, appeared at the initial frosting stage. The effect of operating conditions on the average frost thickness was investigated. As the cooling surface temperature decreased, the average frost thickness decreased. The increase in air velocity yielded an increased frost layer thickness.