Performance evaluation of nanofluid (Al2O3-H2O & Al2O3-H2O, ethylene glycol) based parabolic concentrating solar collector

Abstract

Solar collectors are efficient devices to trap the immense solar energy. Efficiency of such collector is highly dependent upon, nature of working fluid, intensity of solar energy, design and material of the collector and reflector. Nanoscience application plays a major role in heat transfer related problem. In this proposed thesis work, an attempt has been made to enhance the collector’s performance by altering the working fluid, through suspension of the fine sized nanomaterials in the base fluid. α-Al2O3 nanoparticle of 20 nm average size is used. Two different base fluid of H2O (DI) and mixture of C2H6O2- H2O (DI) (40:60 by volume) are used. Four different volumetric concentrations (0.05%, 0.075%, 0.1% and 0.125%) of nanofluid are prepared. Working fluid is made to flow at three different volume flow rate (30 LPH, 50 LPH and 80 LPH. Effect of different working fluid and of different flow rate on collector’s overall efficiency is studied through both experimental and CFD analysis. CFD analysis is carried out using ANSYS FLUENT 14.5. Solar flux is modeled using solar load cell and solar ray tracing. Three dimensional temperature contours is obtained and thus outlet temperature is recorded from within. It has been observed that there is improvement in instantaneous efficiency, thermal efficiency and in overall efficiency, when nanofluid is replaced by the water. Also an improvement of about 9.31%, 11.87%, and 13.98% in the collector’s overall efficiency is seen, when alumina – water nanofluid of 0.125% vol. conc. is used as compared to water at a flow rate of 30 LPH, 50 LPH and 80 LPH respectively. While, when water-ethylene glycol mixture is replaced by 0.125% vol. conc. Al2O3- C2H6O2- H2O (DI) nanofluid, an improvement of about 14.9%, 15.81% and 16.7% is reported at 30 LPH, 50 LPH and 80 LPH respectively. Enhancement in the performance of the collector is seen, when mass flow rate of working fluid is made to increase. It is also observed that, collector’s efficiency is higher with water-based nanofluid as compared with ethylene glycolwater mixture based nanofluid of same volumetric conc. Also, there is a close agreement between both experimental and simulated results with a maximum difference of about 11%.