Modeling Frost Growth for Subcooled Tube-Array Configurations

Methodology for predicting frost growth trends on a subcooled cylindrical surface is developed and implemented for multitube array configuration. Extension of conventional analysis and a novel technique for understanding frost formation phenomenon on the cylindrical surfaces is proposed; later one takes into account the nonsteady temperature field, which affects the density and thermal conductivity at a local level in the growing frost mass, for more accurate prediction of thermal resistance. The influence of migration of liquid water due to tortuosity effect is also considered. The results due to new model are found to be in good agreement with the data in the open literature. Data for frost thickness ratio (FTR) versus time for a section of array with four (tube) rows in the airstream are presented and thoroughly analyzed. The trends of FTR noted are complex and considerably dependent on the tube location, temperature of subcooled surface $(Ts)$⁠, airflow velocity $(Ua)$⁠, and the relative humidity $(RHa)$ values. Approximate ranges for important parameters are $−30≤Ts≤−5.0°C$⁠, $1.0≤Ua≤5.0m/s$⁠, and $0.20≤RHa≤0.80$⁠. Presented analysis and the results are valuable in order to predict probable locations and precursors to partial or complete choking of airflow passages due to frost deposition in the evaporator coils.