Numerical prediction of heat transfer characteristics based on monthly temperature gradient in algal open raceway ponds

This paper presents a novel empirical correlation to estimate the heat transfer in raceway ponds for different pond sizes and depths. The correlation involves the calculation of Nusselt number. Heat transfer in outdoor raceway ponds was modeled with the effects of pond design, hydrodynamics, and environmental conditions. Monthly average water temperature, Nusselt number, and Prandtl number were used to examine the heat transfer phenomena between pond and its surroundings. A novel relation was also employed to estimate the amount of monthly evaporated water from the raceway ponds. Different aspect ratios, pond depths, and paddle wheel rotational speeds were considered to evaluate the effect of pond geometry and turbulent mixing on heat transfer. The use of empirical relation is an effective approach in designing raceway ponds to estimate heat loss in ponds. Algal productivity decreased with increasing amount of evaporated water. Moreover, the environmental conditions, pond design, and turbulent mixing significantly affected the heat transfer rate and the optimum water temperature for algal growth.