Influence of the production method on the thermophysical properties of high temperature molten salt-based nanofluids

Abstract The potential use of molten salt-based nanofluids as thermal energy storage material in Concentrated Solar Power plants has gained attention over the last years due to their enhanced storage capacity. The possible effects of the salt-based nanofluid production at industrial scale have not been yet investigated, as this could influence the nanoparticles agglomeration and therefore their thermal and flow properties. Four methods were evaluated for the production of solar salt-based nanofluids containing 1 wt% of silica nanoparticles. The particle size distribution, the stability, the rheological behaviour and the specific heat of the samples were measured. Nanofluids prepared by means of a dry mixing method presented the lowest viscosity, trimodal particle size distribution and lack of stability. The commonly used dissolution method coupled with oven drying in a petri dish as well as the ball milling method presented non-Newtonian behaviour and intermediate values of particle size and stability. The new spray drying method proposed provided a monomodal particle size distribution with high stability but the highest viscosity and shear thickening behaviour. Results suggest that the four methods evaluated are appropriate for specific heat enhancement (up to 21.1%) but a commitment between stability and viscosity has to be achieved.