A spray evaporation type solar still

Abstract

The single effect basin type solar still has been for long the cheapest way to produce drinkable water from sea water using solar equipment (Howe and Tleimat, 1977). Nevertheless the operating efficiency is low, around 35 %, due mainly to the rejection to the atmosphere of the latent heat of condensation and consequently the production is also low, less than 5 1/m 2 day for a good insolation climate. Furthermore the device presents some operation problems like condensation on the inner side of the glass and algae growth both decreasing the radiation absorption of the basin, and others. Several attempts have been made to increase production, based mainly on the utilization of several evaporation stages using in each stage the latent heat of condensation rejected by the preceding stage (Férnandez and Chargoy, 1990, Joyce et al., 1993). Together with the recover of the latent heat one can increase the evaporation area either by utilizing a fabric where the previously heated salt solution circulates (Baumgartner et al., 1991) or by using some kind of high contact surface material like sponges or thorn bushes (AQUASOLAR, 1988). Another possibility of increasing the evaporation area is just by spraying the salt solution in air and then condensate the moisten air. The present paper describes the details of construction of a device based on spray evaporation and presents the results obtained in laboratory using water previously heated by electric resistances. The experimental results where then used to tune a computational model of the chamber [6] to obtain the performance (daily production and energy consumption) of the system when connected to a CPC solar collector. Testing of the device with CPC collectors will be carried on in the summer of 94.