Experimental study on the thermal performance of a KNO2-KNO3 mixture in a trapezoidal solar pond.

Salt gradient solar ponds (SGSPs) are thermal devices used for storing solar energy for low-temperature applications. The thermal performance analysis of an SGSP was investigated experimentally by artificially establishing a density gradient with sodium chloride (NaCl) and a mixture of potassium nitrite and potassium nitrate (KNO2-KNO3) solution under prevailing weather conditions in Salem, India. The solar pond was trapezoidal and constructed of plywood. The sides of the pond were completely covered with polythene sheets and given a black coating. The experiment was conducted over four months, and its thermal performance was noted. The outcomes of the experimental work showed that the solar pond with KNO2-KNO3 gives a temperature difference of approximately 35 °C between the lower convective zone (LCZ) and upper convective zone (UCZ) and observed maximum temperatures of 66 °C and 57 °C in the heat storage zone of the KNO2-KNO3 and NaCl solar ponds, respectively. Energy storage in the LCZ with KNO2-KNO3 was higher than that in the LCZ with NaCl, owing to the high-volume heat capacity of KNO2-KNO3 and the maximum temperature difference was approximately 9 °C. The energy efficiencies of the LCZ for NaCl and KNO2-KNO3 were 25 % and 33.5 %, respectively. [ABSTRACT FROM AUTHOR]