Heat transfer and temperature distribution of a water droplet during phase transition

Frost growth on heat exchanger surfaces is a common problem for heat pumps operating in heating mode. Frost is detrimental to heat pump capacity and efficiency and occurs because the outdoor heat exchanger (evaporator) is operating at temperatures below freezing under conditions of low ambient temperature and high relative humidity. Here, a two-dimensional numerical model was developed to predict the transient temperature field and the average heat fluxes during the freezing of a hemispherical water droplet resting on a flat horizontal surface. The heat transfer in the droplet was assumed to be conduction only with a forced convection boundary condition at the surface. Internal convection within the droplet was neglected. A limited validation of the model was conducted. Results were compared with Neumann`s classical solution for phase change problems and previously published results of solidification of Na{sub 2}Co{sub 3}. Comparisons of model predictions, analytical solutions, and experimental data revealed that the model successfully simulated the temperature field for liquid, solid, and phase transition regions. An experimental apparatus was constructed to study freezing of water droplets on a cooled copper surface. Comparison of the model with experimental measurements on a 1.3 mm diameter droplet indicated that the model slightly underpredicted transientmore » temperature decrease in the droplet.« less