Frost formation on the fins of outdoor evaporators of heat pump systems degrades system efficiency. Several experimental and theoretical studies investigated using hydrophobic and hydrophilic surface coatings to inhibit frost formation, with promising results; however, most of the models available consist of empirical correlations.

This paper presented an update to the droplet condensation and growth portion of the comprehensive, three-stage frost model from Harges and Cremaschi (2018b). The updates include a model for droplet coalescence, which seems to have significant impact on droplets that grow larger than 125 µm. It also includes a new freezing time correlation. With these two updates, the model predictions agreed well with new data of large droplets forming on flat aluminum surfaces at high surface temperature from the present work as well as the data of small droplets on low surface temperatures from previously published studies in the literature.