Real‐time thermal performance investigation of a thermal energy storage integrated direct absorption solar collector under tropical climate

Abstract

In the last two decades, metallic particles of nano sizes (~10−9 m) have been tested profoundly in volumetric absorption solar collectors (VASC) due to their excellent optical properties and broadband absorption in the entire solar spectrum. However, very limited studies are available for understanding the performance of integrated energy storage VASC systems using nanofluids. For the experimental work presented here, a hybrid nanofluid of gold nanoparticles in Azadirachta indica leaves extract has been synthesized by chemical route. The prepared hybrid nanofluid has shown good absorption in 400 to 700 nm wavelength range and hence achieved high photo‐thermal conversion efficiency for tested VASC system. Furthermore, commercially available paraffin wax is used as a phase change material (PCM) in thermal energy storage (TES) and further integrated with VASC to analyze the thermal performance of the system even after sunshine hours. The real‐time experiments were conducted using different working fluids, and at three mass flow rates, that is, 0.008 kg/s, 0.016 kg/s, and 0.033 kg/s, respectively, during mild winter days in the tropical climate of India. The study revealed a photo‐thermal efficiency enhancement of about 17.1% when hybrid heat transfer fluid was used in the VASC system with TES as compared to base fluid water but without TES. During the heating period, the maximum thermal gain of the hybrid nanofluid was observed to be about 15°C higher than the ambient temperature at mass flow rate of 0.033 kg/s. Thermal efficiency enhancement of about 23.8%, 24%, and 24.1% was observed with hybrid nanofluid compared to base fluid water at a mass flow rate of 0.008 kg/s, 0.016 kg/s, and 0.033 kg/s, respectively, when PCM was kept inside the tank. Furthermore, a maximum zero loss efficiency of 83.8% was estimated at an optimal mass flow rate of 0.033 kg/s for the TES‐integrated VASC system.