Abstract:
A new three-zone heat extraction system and its analytical model for maximizing the thermal
power output of salt gradient solar ponds against a given volume is proposed. The present
study considers internal heat exchangers installed within the non-convective zone (NCZ),
lower-convective zone (LCZ), and the ground below the pond. The work is validated
against a simplified version of the model (eliminating ground and bottom-zone heat extractions) available in the existing literature. Contrary to the conventional practice of optimizing only the middle-zone pond thickness, here, the newly proposed expression is used to find
ideal values of both the middle- and bottom-zone thicknesses of the pond along with its
cross-sectional area. The present work acknowledges that although the three-zone heat
extraction system is the best, yet if a choice for two-zone heat extraction is to be made
between the NCZ–LCZ and ground–LCZ, then the former is a better alternative. The
power output is observed to increase asymptotically with mass flow rates of the three
heat exchangers. However, their values must lie much below their theoretical asymptotic
limits and their selection is regulated by constructional and operational constraints.
These involve a minimum pond depth to offset surface evaporation, ground seepage
water loss, and constraints preventing turbulent flow in heat exchangers to reduce friction
loss and pumping power. This work recommends using three heat exchangers instead of
either one or two and provides cardinal guidelines to extract heat in an ideal manner for
a fixed solar pond volume.
