Abstract
Salinity gradient solar ponds can be used to store heat by trapping solar radiation. The heat can then be employed to drive various industrial applications that require low-grade heat. In this study, a comprehensive finite difference transient model has been developed incorporating many processes that affect the performance of a solar pond to predict the hourly temperature distribution. The model includes novel approaches to simulation of both the Heat Storage Zone (HSZ) and the Upper Convective Zone (UCZ) where in addition to convective, evaporative and radiative heat losses, the cooling effect of adding freshwater to the surface of the pond is taken into account. The HSZ is treated as one layer, with uniform temperature, in the finite difference method. A solar pond of 100 m2 surface area is simulated for southern Turkey. The results indicate that, if the operation starts on the first day of June, the HSZ would take 65 days to reach the boiling point while this would be 82 days if the operation commences on the first day of December. The simulations highlight that 41-47 litres of freshwater will need to be supplied to the UCZ daily and the associated cooling effect of such addition is approximately 10 times larger than the convective heat loss in the first 65 days of operation. In addition, as 22.4% of the incoming radiation in the form of long wavelength radiation, is absorbed within the top 1 cm of the pond, there is a sharp increase in the temperature of the UCZ creating a hot-zone which slowly moves downwards to the Non-Convective Zone (NCZ) and eventually the HSZ. Hence, the HSZ does not initially prevail as the hottest zone in the pond. However, as the temperature rises and the pond approaches pseudo-steady state, the hot-zone slowly moves downwards and finally reaches the HSZ. This phenomenon is consistent with experimental studies and proves the imprecision of pseudo-steady state models. Furthermore, the HSZ becomes more resistant to losing the accumulated heat to the layers above as its temperature increases due to the better establishment of the NCZ as the insulator for the HSZ.