RESUMEN
Owing to their superior optical and thermal properties over conventional fluids, nanofluids represent an innovative approach for use as working fluids in direct-absorption solar collectors for efficient solar-to-thermal energy conversion. The application of nanofluids in direct-absorption solar collectors demands high-performance solar thermal nanofluids that exhibit exceptional physical and chemical stability over long periods and under a variety of operating, fluid dynamics, and temperature conditions. In this review, we discuss recent developments in the field of nanofluids utilized in direct-absorption solar collectors in terms of their preparation techniques, optical behaviours, solar thermal energy conversion performance, as well as their physical and thermal stability, along with the experimental setups and calculation approaches used. We also highlight the challenges associated with the practical implementation of nanofluid-based direct-absorption solar collectors and offer suggestions and an outlook for the future.
RESUMEN
Present environmental issues force the research to explore radically new concepts in sustainable and renewable energy production. In the present work, a functional fluid consisting of a stable colloidal suspension of maghemite magnetic nanoparticles in water was characterized from the points of view of thermoelectrical and optical properties, to evaluate its potential for direct electricity generation from thermoelectric effect enabled by the absorption of sunlight. These nanoparticles were found to be an excellent solar radiation absorber and simultaneously a thermoelectric power-output enhancer with only a very small volume fraction when the fluid was heated from the top. These findings demonstrate the investigated nanofluid's high promise as a heat transfer fluid for co-generating heat and power in brand new hybrid flat-plate solar thermal collectors where top-heating geometry is imposed.
RESUMEN
Direct absorption solar collectors (DASC) convert solar energy into heat energy and transfer this heat energy to a carrier fluid. Numerical and experimental studies have shown that replacing the absorber medium with nanofluids in DASC increases the efficiency of solar collector significantly. Present work investigates the dispersion stability, optical and thermal properties of reduced few-layered graphene oxide (rGO) dispersed nanofluids for DASC. The synthesis of rGO was carried out by hydrogen exfoliation of graphene oxide at 200 °C. As-synthesized rGO was suitably functionalized to impart the hydrophilic nature. Different characterization techniques were employed to analyze the surface morphology of the sample. Nanofluids were prepared by dispersing calculated amount of functionalized rGO in DI water and ethylene glycol. Optical properties study reveals that the nanofluids exhibit good absorption ability over base fluids. The extinction coefficient of nanofluids showed significant improvement even at low concentration. Furthermore, the temperature dependent thermal conductivity study with different volume fractions, carried out for DI water and ethylene glycol-based nanofluids, shows considerable enhancement.