Formation and maintenance of salinity gradient in a solar pond using brine injection technique for linear stratification

Solar pond is a stratified region which stores solar energy in the form of thermal energy up to 95°C in its saline storage zone. This energy is used in various industrial applications ranging from electricity generation and desalination to refrigeration and hot water consumption. The ability of a pond to collect and store thermal energy in storage zone is dependent on effective stratification to suppress natural thermal convection. Diffusion and high temperature gradients result in encroachment of convective zones and development of additional internal convective zones. This results in degradation of stratification hence reducing the thermal efficiency of solar pond. In this scenario, maintenance of salinity gradient comes into play which involves monitoring of different parameters of the stratified region and injecting the fluid through diffusers controlled by feedback and control mechanism. Over the past few decades various methodologies have been developed for optimized maintenance of the stratified region. This research has thoroughly analyzed the gradient maintenance techniques, specifically focusing on injection mediums and their effects on the salinity gradient maintenance. The two configurations of injection medium i.e. injection of highly turbulent columnar jets into homogeneous convective zones and the injection of low exit Froude number fluid through a disk-shaped diffuser (most common) are elaborately analyzed and compared. Moreover, the effect of size & shape of the injector slots and followed by fluid velocity of injector on the flow pattern exiting the injection medium has been thoroughly analyzed. The analysis and comparison of different gradient maintenance and formation techniques show that flow discharge through a half disc shaped diffuser with rectangular slots at Froude No ranging from 12–18 is optimum for the stratified region. The analysis of an optimized injection mechanism has enabled formation and maintenance of a linearly distributed stratified region in the non-convective zone (NCZ) resulting in more heat collection in the lower convective zone (LCZ).