Abstract
The thermal conductivity of microfluids comprising Ni3(μ3-ppza)4Cl2 metal string complex (MSC) microparticles in an aqueous glycerol solution was investigated using the transient hot-wire method. A comparative analysis of the thermal-conductivity enhancements of microfluids and nanofluids revealed that the best results were achieved using microparticles of monocrystalline MSCs Ni3(μ3-ppza)4Cl2 as well as Ni5(μ5-pppmda)4Cl2 micro- and copper nanoparticles. Compared to the base fluid, the thermal-conductivity enhancements were 72% for Ni3–water–glycerol, 53% for Cu–water–glycerol, and 47% for Ni5–water–glycerol. It is shown that the high thermal-conductivity enhancement achieved with Ni3 microfluids is a result of higher stability in compare with nanofluid due to the lower density of the microparticles and the formation of particle assemblies. Therefore, the formation of hydrogen bonds between the MSC particles (through their organic fragments) and water molecules, takes place. Colloidal structure of Ni3-microfluids has a significant impact on their thermophysical properties.
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