Experimental measurements of thermal conductivity of alumina nanofluid synthesized in salt melt

Nanoparticles were synthesized in-situ using a simple one-step synthesis protocol from a cheap additive, mixed apriori in a high temperature salt melt (solar salt, NaNO₃-KNO₃). The thermal conductivity of the nanofluid was measured using a standardized concentric cylinder (annulus) test apparatus under steady-state conditions. The thermal conductivity of the salt melt was enhanced by 20∼ 25% due to generation of nanoparticles in-situ from the additive. The level of enhancement was found to be insensitive to temperature but significantly exceeded the predictions from models in the literature. Materials characterization (using electron microscopy) showed the formation of percolation networks by secondary nanostructures in the molten salt nanofluid samples (that were induced by the nanoparticles generated in-situ). The enhancement in the thermos-physical properties of the salt-melt nanofluids can be attributed to the formation of these secondary nanostructures (which form a third phase).