Numerical simulation of windshield defogging process

Abstract

A suite of routines for the prediction of environment moist condensation and evaporation on solid surfaces is presented. The physical problem requires the solution of the airflow field along a (cold) solid surface, the evaluation of the unsteady conduction through the solid itself, and the development of a suitable model for the heat and mass transfer through the thin water layer on the fogged surface. The routines for the unsteady simulation of the water layer development are designed as a purely interfacial procedure, minimizing the exchange of information with both the flow and the conductive solver. This allows the coupling with different solvers. Here, the model is used in connection with a commercial computational fluid dynamics solver, in order to predict the defogging process of a car windshield. The water layer is modelled as a collection of closely packed tiny droplets, leaving a portion of dry area among them. The effect of the contact angle is taken into account, and physical assumptions allow the local ratio of the wet surface to the dry surface to be defined for both the fogging and the defogging process.