23 September 2011

CONDENSATION AND ICING ON COOLED SURFACES


Condensation and subsequent icing are phenomena that have an influence on many applications, either as an intended process, like condensation in the heat extraction from exhausts of thermal power plants, or unwanted occurrence, for example at air-source heat exchangers for heat pumps, where accreted ice causes deteriorated performance and ultimately blockage of the whole device. There exist already thorough studies, on the growth of water films and ice layers on cooled surfaces, but what is still badly missing is a systematic investigation of the onset of condensation and icing. These onset processes are governed by the laws of heterogeneous nucleation, a theory which is not very well established for technological applications. Therefore the present work firstly consists of experiments on condensation and icing on cooled surfaces under varying conditions. Secondly, the captured experimental data are used as input for computational fluid dynamics simulations, coupled with a boundary condition for the cooled surface based on classical nucleation theory as a model for the onset of occurring water droplets and ice crystals.