Experimental Measurement of the Effect of Particle Concentration on the Specific Heat Capacity of Silica Nanofluids

摘要

Controversies abound in the literature for the specific heat capacity data involving nanoparticle suspensions dispersed in various solvents (nanofluids). Reports show significant enhancement in the specific heat capacity on mixing with nanoparticles for ionic liquids (e.g., molten salts, [Cnmim][NTf2], etc.) and oils (e.g., poly-alpha-olefins/PAO) but substantial reduction for polar liquids (e.g., water, Ethylene Glycol/ EG, etc.). Recent studies have attributed the anomalous enhancement in specific heat capacity to the morphology of the solvent molecules that are adsorbed on the surface of the nanoparticles (leading to the formation of a “compressed nano-layer” - with higher density than the surrounding bulk phase of the solvent) - which in turn act as thermal capacitors with elevated levels of energy storage density. Analytical estimates show that the compressed nano-layer contributes only a fraction of the net enhancement of the specific heat capacity data of the nanofluids. In this study, a detailed parametric experimental study was performed to investigate the effect of the particle concentration on the specific heat capacity of silica nanofluids using the T-history method. The results showed progressive increase in the level of specific heat capacity enhancement of the propylene glycol nanofluid samples on increasing the mass concentration of the nanoparticles. This result is consistent with general trend of specific heat capacity change observed for different types of solvents reported in the literature. The result implies that the transport mechanisms modulating the specific heat capacity enhancement of nanofluid samples is dominated by chemisorption of the ions from the solvent phase on to the surface of the nanoparticles.