Abstract:
The transient performance of a salt gradient solar pond, which experiences heat extraction from both gradient
and storage regions has been studied for annual performance via accounting for the overall heat transfer coefficient across heat exchangers. The proposed method after reduced complexities is satisfactorily validated with
theory and experiment-based results of pertinent literature. The novelty of the work lies in the fact that, the
temperature drop across both non-convective and lower-convective zone exchanger surfaces has been accounted
by using a local time and space dependent heat transfer coefficient. Here, it takes into the consideration free
convection from the pond to the exchanger surface, and forced convection from the exchanger surface to flowing
working fluid. Further, temperature variation of thermo-fluidic parameters of water involving, viscosity, density
and thermal conductivity is considered. Detailed numerical investigation reveals that by neglecting this coefficient which is assumed in conventional studies, it can lead to significant errors in the prediction of transient
temperature profiles in the pond and the exchangers. Calculations reveal an error of about +69% in the annual
extraction efficiency and about − 9% in entropy production if the conventional assumption is used as opposed to
realistic technique presented herein. Interestingly, the present study reveals that there is an optimum radius of
exchanger pipe in each of non-convective and lower convective zones that maximises the annual extraction
efficiency. This work presents a useful analysis to assess multi zone extraction from solar ponds under transient
state in a more practical and accurate manner.
