Numerical study on thermal performance of a nanofluid based flat plate solar collector

Flat plate solar collectors (FPSCs) are commonly used devices to convert solar radiation into useful heat for a variety of thermal applications. Due to the lower thermal efficiencies of these systems, recently, nanofluids are suggested to be used in FPSCs as the working fluid to enhance their energy harvesting potential. This study introduces a transient heat transfer approach for determining the thermal inertia of each component such as glass, trapped air, absorber and working fluid for nanofluid based flat plate solar collectors. The analyses were carried out with water and three different volumetric concentrations of alumina nanoparticles as 1, 2 and 3 volumetric percent. Mass flow rate of the heat transfer fluid is varied in a wide range, between 0.004 and 0.06 kg/s, to demonstrate the effect of thermophysical properties at different flow Reynolds numbers. The results demonstrate that outlet temperature of the FPSCs increases with increasing particle concentration. Moreover, the outlet temperature decreases with increasing mass flow rates. On the other hand, thermal efficiency of the FPSCs increases with increasing mass flow rates regardless of the type of heat transfer fluids. However, nanofluids can increase the thermal efficiency of the FPSCs at lower mass flow rates and the thermal efficiency increases with increasing particle concentration. Beyond a critical mass flow rate the base fluid becomes effective working fluid and the thermal efficiency decreases with increasing particle concentration. For the current study, the critical mass flow rate is determined to be 0.016 kg/s.