On thermophoresis modeling in inert nanofluids

• Published in: International journal of thermal sciences Vol. 80; no. 80; pp. 58 - 64
• Main Authors: Eslamian, Morteza, Saghir, M. Ziad
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Masson SAS 01-06-2014; Elsevier
• Subjects: Applied sciences; Binary mixtures; Chemistry; Colloidal state and disperse state; Condensed matter: structure, mechanical and thermal properties; Diffusion and ionic conduction in liquids; Diffusion and thermal diffusion; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fluid flow; Fluids; General and physical chemistry; Heat transfer; Hydrodynamics; Inert; Macromolecules; Mathematical models; Nanofluids; Nanostructure; Nonequilibrium thermodynamics; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Physics; Soret effect; Theoretical studies. Data and constants. Metering; Thermal properties of condensed matter; Thermal properties of small particles, nanocrystals, nanotubes; Thermodiffusion; Thermophoresis; Transport properties of condensed matter (nonelectronic); Soret effect; Nonequilibrium thermodynamics; Hydrodynamics; Thermophoresis; Thermodiffusion; Nanofluids; Thermal diffusion; Forced convection; Nanoparticle; Nanofluid; Natural convection; Modeling; Numerical simulation; Heat transfer
• ISSN: 1290-0729; 1778-4166
• DOI: 10.1016/j.ijthermalsci.2014.01.016

Thermophoresis plays an important role in forced and natural convection in channels and enclosures when nanofluids are used instead of pure fluids. One objective of this work, therefore, is to investigate whether reliable expressions exist for the estimation of thermophoresis data. As the second objective of this work we will show similarities between thermophoresis of nanoparticles and macromolecule dispersed in a base fluid with thermodiffusion of species in binary mixtures. To this end, a nonequilibrium thermodynamics-based expression primarily developed for the estimation of thermodiffusion factor in binary mixtures is extended and applied to thermophoresis in nanofluids. A hydrodynamics-based expression and the nonequilibrium thermodynamic-based expression developed here, are used to estimate the thermophoretic velocity in nanofluids. Validation results suggest that the general form of the hydrodynamics-based equation is valid for thermophoresis of nano-sized and even sub-nanometer particles in liquids; however, the correct prediction of the matching parameter is still unresolved. Also, the nonequilibrium thermodynamics combined with the concept of activation energy of viscous is somewhat capable of estimating thermophoresis coefficient of inert particles and macromolecules of about 1 nm or smaller. The agreement, however, is qualitative.
•Similarities and differences between thermophoresis and thermodiffusion are elucidated.•Two model expressions are introduced for the estimation of thermophoresis coefficient.•One model based on the hydrodynamics theory is introduced and evaluated.•A second model based on the nonequilibrium thermodynamics is developed and evaluated.