A novel procedure for transient CFD modeling of basin solar stills: Coupling of species and energy equations

Abstract

A novel procedure for transient numerical modeling of solar stills is proposed in this study. With no need to specify the glass and water temperatures as boundary conditions, instantaneous weather and irradiance data are the only inputs in the present CFD simulation. The absorption of solar radiation and radiative heat transfer in different components of the solar still are accounted by solving the DO radiative transfer equation. Instead of applying costly multi-phase techniques, species equation for water vapor is solved by coupling with energy equation through user defined functions. In this method, the latent heat of evaporation/condensation is considered as a sink/source term in the energy equation. The required evaporation and condensation rates are calculated by integrating Fick's law on the water and glass surfaces. The latent heat of phase change is assumed to be shared between the two neighboring bodies by introducing a coefficient α with the appropriate value of 0.5. Therefore, transient temperature and concentration distributions and productivity in passive and active solar stills are calculated throughout a day with moderate computational cost. By applying the present method to multi-stage active solar stills, it is shown that increasing the number of stages beyond six is not beneficial.