Nanofluid-based direct absorption solar collector

TLDR

Solar energy is a clean renewable source, but direct absorption collectors are limited by the poor absorption of conventional fluids, and adding nanoparticles to form nanofluids enhances thermal conductivity and radiative properties, potentially raising collector efficiency. The study investigates the performance of direct absorption solar collectors using nanofluids composed of carbon nanotubes, graphite, and silver nanoparticles. Experiments were conducted on nanofluid collectors and the data were compared with a numerical model of a direct absorption solar collector incorporating nanofluids. Efficiency gains of up to 5 % were observed, with a rapid initial rise in efficiency as nanoparticle volume fraction increased, followed by a plateau at higher concentrations.

Abstract

Solar energy is one of the best sources of renewable energy with minimal environmental impact. Direct absorption solar collectors have been proposed for a variety of applications such as water heating; however the efficiency of these collectors is limited by the absorption properties of the working fluid, which is very poor for typical fluids used in solar collectors. It has been shown that mixing nanoparticles in a liquid (nanofluid) has a dramatic effect on the liquid thermophysical properties such as thermal conductivity. Nanoparticles also offer the potential of improving the radiative properties of liquids, leading to an increase in the efficiency of direct absorption solar collectors. Here we report on the experimental results on solar collectors based on nanofluids made from a variety of nanoparticles (carbon nanotubes, graphite, and silver). We demonstrate efficiency improvements of up to 5% in solar thermal collectors by utilizing nanofluids as the absorption mechanism. In addition the experimental data were compared with a numerical model of a solar collector with direct absorption nanofluids. The experimental and numerical results demonstrate an initial rapid increase in efficiency with volume fraction, followed by a leveling off in efficiency as volume fraction continues to increase.