Model for cyclic frosting and defrosting of flat tube heat exchangers: Theoretical analysis and experimental validation

Flat tube heat exchangers are used in heat pump applications for energy-efficient heating due to their compactness. If ambient air is used as a heat source, frost may form on the surface of the evaporator at low ambient air temperatures. If significant amounts of frost accumulate, the heat exchanger must be defrosted, and in flat tube heat exchangers, a part of the melt water is retained between the louvers and fins. Frosting models are used to study heat exchanger performance by characterizing the heat transfer and air-side hydraulic effects on heat exchangers. Previous published models describe the effects of frosting of a dry heat exchanger, neglecting the effects of water retained after defrosting. In this study, a novel, numerical model for a flat tube heat exchanger in cyclic frosting and defrosting operation is developed that considers the transport processes and states of the retained water. To validate the numerical model, experiments on flat tube heat exchangers at different boundary conditions are executed on a test rig. A comparison between numerical and experimental data shows an average deviation of the chosen comparative variables of less than 4%. •Modeling of frosting, refrosting, defrosting, and water retention.•Analysis of the air-side heat transfer area and pressure drop at frost formation.•Experimental validations of cyclic frosting and defrosting heat exchanger models.•Average deviation less than 4% between numerical and experimental data.