Theoretical and empirical study of heat and mass transfer inside a basin type solar still

Heat and mass transfer between the surfaces of the cover and saline water in a solar still occurs through convection (hc,w−gc), evaporation (he,w−gc) and radiation (hr,w−gc). All these three coefficients of heat transfer influence the performance of the solar still, and so they need to be computed accurately. In this study, two recent models for calculating the coefficient of evaporative heat transfer (he,w−gc) have been investigated by taking into account view factors of radiative heat exchange. In the first model (Model 1), the vapour concentration ratio (Cr = he,w−gc/hc,w−gc) depends on different thermodynamic variables inside the solar still. The other model of Cr (Model 2) is a third-order polynomial function of the operating temperature of the solar still (Ti). Results show that Cr has a critical value for Model 1 with no turning point for Model 2 in the considered temperature range. There exists an operating temperature Ti=Tis at which the two models yield the same value of Cr. Estimates of the coefficient of he,w−gc obtained by using Model 1 are higher than those of Model 2 when Ti < Tis, with a reversed trend when Ti > Tis. Model 1 exhibits lower values of the root mean square error.