Phase change in semitransparent droplets and particles heated by convection and radiation
Phase change in a cloud of droplets and beds of particles heated by convection and radiation arises in numerous important technological and materials processing applications. Examples involving evaporation of sprays include fuel droplets combustion devices, fire control using water sprays, irrigation of crops, etc. In materials processing beds of particles (i.e., sand, recycled aluminum, etc.) are melted in furnaces to produce engineered materials. When the heat sources are at high temperature, radiation transfer has to be accounted for in analysis. In this research, phase change of a single particle is considered first to develop understanding of the fundamental heat transfer/phase change processes before tackling melting of a particle bed heating by convection and radiation from above. Evaporation of a droplet (fuel and water) heated by convection and external radiation field is analyzed as examples of application in fuel spray combustion and fire control. The droplets are assumed to be spherical and semitransparent to radiation. Published spectral absorption coefficient data are used in the calculations, and model predictions are compared with available experimental and theoretical results on water, n-heptane and n-decane evaporation. Melting of spherical opaque and semitransparent particles is analyzed, and a thermal model is developed. As an example, fused silica is considered as the material and spectral absorption coefficient data from the literature are used to predict the local spectral irradiance and the local volumetric rate of absorption and emission of radiation as a function of particle diameter and the external radiation source temperature. A model has been developed, extensive numerical results have been generated, but experimental data needed for model validation could not been identified in the literature for validation purposes.
Viskanta, Purdue University.
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