Experimental study of laboratory salt gradient solar pond thermal behaviour (original) (raw)
1988, Heat Recovery Systems and Chp
Aktraet--Experimental studies have been performed on two identical small scale laboratory solar ponds which consisted of rectangular tanks made of reinforced concrete having dimensions 0.40 × 0.40 x 0.90 m, with wall thickness 0.03 m. The measurements have been obtained by operating the pond at one fourth, one third and a half full using 15% and 20% concentrations of the sodium chloride solution. The pond surface was made up by adding fresh water to the brine in the pond. Stable density gradients were developed at room temperatures approximately one month after estabfishment. The ponds were then heated from the bottom to temperatures of 35°C, 40°C, 45°C and 50°C and density profiles as well as temperature profiles were obtained for every operating temperature. Dry dune sand with variable thickness (6era and 12cm) has been used as a thermal insulator around the walls of the pond. In this study, the following effects are considered: the heat transfer from the pond to the surrounding ground; the change of the salt gradient due to the diffusion of salt; the local occurrence of thermal convection. The effect of the variation of the thickn__~__ of the upper, lower and non-convective zones with the variation of the heating temperature and the filling depths of the pond are discTassed qualitatively. It is noticed that the thermal performance of the pond is improved by taking proper care of the above mentioned facts. t a, Greek letters ~.l thermal conductivity of the wall of the pond [Win -t °C -I ] ~.2 thermal conductivity of imulating material [W m -~ °C -~ ] ~.w thermal conductivity of saline water [W m-t °C-t ]
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