Novel key parameter for eutectic nitrates based nanofluids selection for concentrating solar power (CSP) systems

Abstract

A high-performance heat transfer fluid (HTF) plays a crucial role in the overall performance and efficiency of concentrating solar power (CSP) systems for utilizing solar energy. Molten salt-based nanofluids, which may offer a promising solution to help reduce the size and cost of CSP systems, have attracted increasing attention. However, there is still no comprehensive assessment strategy that considers the conflictive effects of adding nanoparticles in HTFs, such as the compromise between energy storage capacity increase and pumping cost increase. In this work, a methodology for nanofluids screening and selection is proposed and a novel parameter (R) is determined to assess the conflictive effect. The parameter (R) considers the ratio between the relative pumping power and the relative energy stored of the nanofluid compared to its base fluid. Three promising eutectics nitrate based nanofluids (NaNO3–KNO3, LiNO3–NaNO3–KNO3, LiNO3–NaNO3–KNO3–Ca(NO3)2) doped with 0.5 wt.% and 1 wt.% silica nanoparticles were selected and evaluated by the proposed methodology. As a result, adding nanoparticles into binary salts always present a negative effect (R = 1.03–1.22) when considering the ratio between the relative pumping cost and the relative energy stored. For ternary salt, adding 1 wt.% silica nanoparticles would be more preferable with a decrease of the parameter (R = 0.89–0.97, R < 1). In terms of quaternary, adding nanoparticles into quaternary does not change the parameter significantly (R = 0.96–1.04).