Numerical analysis of the vertical multiple-effect diffusion solar still coupled with a flat plate reflector: optimum reflector angle and optimum orientation of the still at various seasons and locations

Abstract

The optimum angle of a flat plate reflector and the optimum orientation of a vertical multiple-effect diffusion solar still coupled with a flat plate reflector throughout the year are numerically determined with the assumption that the still is located at the equator and at 10°, 20°, 30° and 40° northern latitude. The optimum orientation of the still which maximizes the distillate productivity of the proposed still was calculated assuming that the orientation of the still is changed once during daytime at southing of the sun. The proposed still has very simple structure and consists of common materials such as thin stainless steel plates, glass plate, cotton cloth, a flat plate reflector and so on, which can be purchased in the developing countries, so the proposed still may be constructed and operated by local technicians in the developing counties. The proposed still consists of a glass cover and a number of vertical parallel partitions with narrow air gaps between partitions, and all partitions except for the outer one are in contact with saline-soaked wicks. Direct and diffuse solar radiation as well as the reflected radiation from the flat plate reflector are absorbed on the first partition, and the evaporation and condensation process is repeated on all partitions to increase the productivity of distillate. The proposed still is assumed to be rotated manually just twice a day (at near noon and before sunrise) to change its orientation and absorb more solar energy on the first partition. We found that the angle of the flat plate reflector should be basically fixed at 10° from horizontal and changed to be 0° during the winter season (around December) at higher latitudes, and the orientation of the still should be adjusted according to month at any latitude. The daily productivity of the proposed still was predicted to be more than 30 kg/m 2day at any latitude throughout the year except for the winter season (from November to January) at 40°N latitude.