Abstract
Laminar flow of ethylene glycol-based silicon nitride (EG-Si3N4) nanofluid in a smooth horizontal pipe subjected to forced heat convection with constant wall heat flux is computationally modeled and analyzed. Heat transfer is evaluated in terms of Nusselt number (Nu) and heat transfer coefficient for various volume fractions of Si3N4 nanoparticles in the base fluid and different laminar flow rates. The thermophysical properties of the EG-Si3N4 nanofluid are taken from a recently published experimental study. Computational modelling and simulation are performed using open-source software utilizing finite volume numerical methodology. The nanofluid exhibits non-Newtonian rheology and it is modelled as a homogeneous single-phase mixture, the properties of which are determined by the nanoparticle volume fraction. The existing features of the software to simulate single-phase flow are extended by implementing the energy transport coupled to the fluid flow and the interaction of the fluid flow with the surrounding pipe wall via the applied wall heat flux. In addition, the functional dependencies of the thermophysical properties of the nanofluid on the volume fraction of nanoparticles are implemented in the software, while the non-Newtonian rheological behavior of the nanofluid under consideration is also taken into account. The obtained results from the numerical simulations show very good predicting capabilities of the implemented computational model for the laminar flow coupled to the forced convection heat transfer. Moreover, the analysis of the computational results for the nanofluid reflects the increase of heat transfer of the EG-Si3N4 nanofluid in comparison to the EG for all the considered nanoparticle volume fractions and flow rates, indicating promising features of this nanofluid in heat transfer applications.
Highlights
Nanofluids are mixtures or suspensions of small particles of order of tens of nanometer in pure base fluids, which after mixing and dispersing the nanoparticles have shown the potential to increase heat transfer in engineering applications
The computational model incorporating coupled fluid flow and energy transport has been implemented in the finite-volume numerical approach to enable simulations in the framework of CFD
In contrast to most previous studies, the rheology of the nanofluid depends on the nanoparticle volume fraction and the non-Newtonian shear thinning nanofluid rheology has been taken into account
Summary
Nanofluids are mixtures or suspensions of small particles of order of tens of nanometer in pure base fluids, which after mixing and dispersing the nanoparticles have shown the potential to increase heat transfer in engineering applications. The present study focuses on computational modelling and analysis of a laminar flow of a non-Newtonian nanofluid (ethylene glycol-based silicon nitride (EG-Si3 N4 )) in a horizontal pipe with respect to the forced convection heat transfer. The obtained experimental results reveal the non-Newtonian shear thinning behavior of the nanofluid, a simple linear increase of thermal conductivity with volume fraction of nanoparticles, as well as a high enhancement of electrical conductivity and an increase of optical properties (refractive index, absorption) with volumetric concentration of nanoparticles Such behavior of the properties renders the EG-Si3 N4 nanofluid as being convenient in applications for heat transfer, such as heat exchangers and thermal energy storage, and for applications where enhanced electrical and optical properties are of importance, such as electromagnetic flow meters or solar collectors. The results show that the heat transfer of the EG-Si3 N4 nanofluid increases in comparison with the ethylene glycol as the base fluid
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