Frost-Air Interface Characterization Under Natural Convection

Surface frosting from atmospheric humidity under natural convection is encountered in conventional refrigeration systems, cryogenic surgery, and cryogenic stress relief of die casting metal forming applications. To advance the predictability of frost initiation and formation processes, this study reports a microscopic analysis of frost growth on a flat surface during the onset period of freezing when subcooled droplets are formed and changed to the ice phase. The onset of freezing is quantified by the mean droplet size and ice particle fractions at a critical time (when water droplet freezing point is reached) with the aid of a video microscope. An early-stage frost formation model with effective parameters is demonstrated to provide the important information for the transition to the steady-growth model. The model results are compared with the measured air-frost surface temperatures at different cooling and ambient boundary conditions, using holographic interferometry. The comparison between the model prediction and experimental results demonstrates the sensitivity of effective parameters in simulating the frost thickness and air-frost interface temperature.