Some Insight into Frost Growth in Turbulent Moist Air Flow using Direct Numerical Simulations

We developed a new model to predict frost growth over a flat plate maintained at subfreezing temperatures and subjected to humid turbulent air flow. The model employs a dynamically coupled air-frost interface. The air phase has been modeled using direct numerical simulations, while the frost phase has been modeled from first principles using the conservation equations of mass and energy. Coupling of the two phases is done using either the immersed boundary method or by deforming the bottom boundary and using a body-fitted grid. Due to the vastly different time scales between the fast developing turbulent flow and the much slower frost phase, a slow-time acceleration technique has been implemented to make the simulations feasible by accelerating the frost growth process. The model has been validated against laboratory experiments and then used to predict frost growth under a variety of free-stream and plate conditions. We observed that the Nusselt and Sherwood numbers could be properly scaled so as to become primarily dependent only on the Reynolds, Prandtl, and Schmidt numbers. A series of simulations covering a range of shear Reynolds numbers between 100 and 2000 were then used to extract the Nusselt and Sherwood number dependencies on the Reynolds number.