Natural convection heat transfer and fresh water yield in vertical plate cavity with film evaporation and raw water reservoir

A triple-effect regeneration solar distiller with raw water reservoir is designed and its operation principle is introduced. Experiments with different heating power were carried out with chrome steel strip heater for 6.5 h. In each stage, the temperature and fresh water yield of distiller were measured. The total fresh water yield of each stage in one day and the relation between evaporation rate per unit area and temperature in the vertical distiller were obtained. The experimental results with constant heating power shows that the performance ratio of the evaporation can reach 1.81 with 600 W heating power and its optimal heating energy per day is about 14 MJ. Therefore, it is suggested the area of matched solar collector is 1.5 m ² when the equipment is operated in general weather. A theoretical model is proposed in this study, which can be used for natural convection heat and mass transfer with film evaporation and raw water reservoir inside the vertical cavity. An empirical formula between Nusselt number and Rayleigh number is obtained, which is suitable for calculation of vertical plate cavity with film evaporation and raw water reservoir.