Enhancing the Thermal Performance of Solar Air Heaters Using Heat Storage Medium: An Experimental Study With Energy, Exergy, and Economic Approach

Abstract

A solar air heater (SAH) is a simple device that collects solar radiation and transfers it to the processed air generally used in several thermal engineering applications such as space and industrial process heating and food drying, but its utilization is only during sunny hours. Among the methods of ameliorating its employing to heat air during the off-sunshine period is through the addition of heat storage medium inside the SAH for storing the sun's radiation as thermal energy. The main objective of this experimental study is to predict the effect of the heat storage medium on the thermal performance of SAH. To achieve this goal, three different configurations of SAHs were designed and constructed in the Laboratory of Electro–Mechanic Systems, namely, traditional SAH with natural circulation (T-SAH), SAH with a centrifugal air blower (F-SAH), and SAH with a centrifugal air blower and coupled with an internal heat storage medium (FS-SAH). They were tested and compared under the same ambient conditions of Sfax, central-eastern Tunisia. Experimental results showed that the T-SAH gives higher temperatures than the F-SAH and FS-SAH during the period from 8 a.m. to 3 p.m. From 3 p.m. to 7 p.m., the temperatures of FS-SAH are the highest when compared with the other two SAHs. Through this period, the thermal energy per unit time obtained by FS-SAH, F-SAH, and T-SAH is 2.15 kW, 0.23 kW, and 0.22 kW, respectively. Due to the use of salt water as a heat storage medium, the thermal energy per unit time of FS-SAH is enhanced by 1.92 kW (corresponding to 89.3%) and 1.93 kW (corresponding to 89.77%) higher than the F-SAH and T-SAH, respectively. The FS-SAH offers higher thermal and exergy efficiency as compared to the T-SAH and F-SAH during the same period. The economic evaluation showed that the money saved by FS-SAH is 96% and 89.51% higher than the T-SAH and F-SAH, respectively. Therefore, the employ of salt water as a heat storage medium is a positive attempt to enhance the thermal performance of SAHs during the off-sunshine period of this experimental testing.