Photothermal Energy Conversion Enhancement Studies Using Low Concentration Nanofluids

The present study aims to develop a compact experimental facility to trap solar energy. Line focusing concentrators, i.e., Fresnel lens and secondary reflectors, are coupled to enhance the photothermal conversion efficiency. Two types of receiver tubes are used, a plain copper tube and an evacuated glass tube embedded with a copper tube. Surfactant-free multiwalled carbon nanotubes-Therminol55 nanofluid with concentrations of 25, 50, 75, and 100 ppm are used in this study. The characterization of the nanoparticles and nanofluids is presented. In the visible range, a maximum absorbance and extinction coefficient of 0.75 and 1.7 cm(-1) are obtained for 100 ppm concentration. The thermal conductivity is also enhanced by 6.29% compared to base fluid. A maximum fluid temperature of 78.15 and 89.58 degrees C is observed for plain receiver tube and receiver tube in evacuated space, respectively, and the corresponding efficiencies are 12.65 and 17.36%