Thermophysical properties and stabilization mechanism of nano- and microfluids with [Ni5(μ5-pppmda)4Cl2] metal string complex particles

Abstract

The results of thermophysical properties studies and stabilization of nano- and microfluids prepared on the basis of glycerol aqueous solutions are presented. The results of determination of thermal conductivity, rheology, interfacial tension and stability of the studied solutions are presented. Cu, Ni and Al nanoparticles were used for the preparation of nanofluids, and microparticles of the metal-string complex [Ni5(μ5-pppmda)4Cl2] synthesized in laboratory conditions were used for the preparation of microfluids. It was shown that the Ni5 microfluid has a higher stability than the studied nanofluids due to the formation of hydrogen bonds, lower density of microparticles and the formation of ensembles of particles whose sizes are determined by the buoyancy conditions. The rheology of Ni5 microfluids exhibiting thixotropic behavior is also significantly different. The investigated Ni5 microfluids exhibited almost the same increase in thermal conductivity compared to the base fluid as the nanofluids. It is shown that the increase in thermal conductivity of the microfluids is related to the single-crystal structure of the used microparticles. An equation predicting a 10-fold increase in thermal conductivity for Ni5 nanofluid solutions as compared to microfluids is proposed. Keywords: nanofluid; microfluid; thermal conductivity; viscosity; stability.