Numerical assessment of transition metal nitrides nanofluids for improved performance of direct absorption solar collectors

Abstract

Abstract Metallic nanostructures have attracted the attention for solar applications due to their high optical absorption cross-section, which is associated to the localized surface plasmon resonances phenomenon. In this work, the thermo-optical performance of a direct absorption solar collector using working-fluids composed of TiN, ZrN, and HfN nanospheres in an aqueous medium was evaluated using Mie theory and numerical solutions of a two-dimensional heat transfer model. The influence of nanoparticle size, volume fraction, collector height, and working-fluid temperature for the collector thermal and exergy efficiencies was investigated. Results revealed the transition metal nitrides nanoparticles have small scattering cross-sections and broad absorption peaks, matching well the solar radiation spectrum. The thermal efficiency is higher than 80% for collectors with all three nitrides nanoparticles. The collectors using TiN, ZrN, and HfN nanofluids exhibit thermal performance 50.4%, 36.5%, and 41.8%, respectively, higher than with Au nanofluid, which is a reference plasmonic material for solar applications. Moreover, collectors using transition metal nitrides reach higher outlet temperatures than with gold, leading to higher exergy efficiencies with low volume fraction. The maximum exergy efficiencies of DASC using TiN, ZrN, and HfN NF are 6.3%, 5.2%, and 5.6%, respectively, while using Au NF is 2.9%. The superior performance in a low-concentration regime allows the application of nanoparticles in the collector without increasing the required pumping work. The findings related to the photo-thermal efficiencies of transition metal nitride nanofluids, in addition to their low cost and high chemical stability, make them suitable to use for solar-related heating technologies.