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Investigation of the effect of particle stability on the transport properties and thermal behavior of ethylene glycol-water/ SiO2 binary nanofluids

Nanofluids (Nfs) are considered as an effective working media in different thermal processes. Over the years, much attention has been paid to the problem of nanoparticle stability in base fluids in an unconfined area of research, especially in the field of thermal applications. There is still concern about the stability of nanoparticles and their effects on the transport properties and thermal performance in thermal systems. In the present paper, the transport properties and thermal behavior of ethylene glycol-water/ SiO2 binary Nfs are investigated in two sections, considering the effect of particle stability and size growth. The first section covering the experimental work, which includes the preparation and characterization of the Nfs where different percentages of base fluids at different pH values are used for this purpose. The characterization of the Nfs explains the effect of the zeta potential on the particle size distribution and the hydrodynamic diameter of suspended particles. The second section involves the theoretical study, where the transport properties and thermal behavior of the Nfs are estimated taking into consideration the effect of the particle stability and size growth. It is found that the binary Nfs that contain different types of base fluids show different stability behavior at different pH values at the same particle concentration. Ethylene glycol-water/ SiO2 binary Nfs at pH = 9 contain a low hydrodynamic diameter of suspended particles, and Nfs have good stability behavior. On the other hand, the Nfs at pH = 2 contain the maximum size of the particle hydrodynamic diameter. The Nfs that include 25% water + 75% ethylene glycol show a better stability behavior in comparison with other types of Nfs that included 75% water + 25% ethylene glycol. Particle size growth shows a significant effect on the transport properties (thermal conductivity and viscosity) as well as the particle-fluid interaction Nusselt number, Biot number, and convection heat transfer coefficient.