Effect of Thermal Buoyancy on the Recirculating Flow in a Solar Pond for Energy Extraction and Heat Rejection

An analytical and numerical study is carried out to determine the effect of buoyancy, resulting from temperature differences, on the recirculating flow arising in enclosed regions, such as the surface and storage layers of a salt-gradient solar pond, due to the discharge of fluid into it. The study investigates the time-dependent flow, considering an initially isothermal or thermally stratified fluid region, and the approach to the steady-state circumstance. Various flow configurations and boundary conditions, of particular relevance to energy extraction and heat rejection in solar ponds, are considered. The governing parameters, particularly the buoyancy parameter, are varied to determine the dependence of the flow field on these. Both laminar and turbulent flow are considered and numerical results are obtained for the velocity and temperature fields in the pond. Several interesting features are observed, particularly the strong effect of thermal buoyancy on the flow in the range of physical variables of practical interest and the effect of the flow on the growth and decay of a stable thermal stratification in the enclosed region. The effect of a periodic heat input into the region is studied. The study also considers relevant one-dimensional steady and transient analytical models for the thermal field and results are presented to indicate the range of validity of such simple models. The results obtained are also compared with earlier numerical and experimental studies of this flow circumstance and a fairly good agreement is observed. The relevance of the work to practical solar ponds is also outlined.