Mixed convection of alumina–water nanofluid inside a concentric annulus considering nanoparticle migration--颗粒学报PARTICUOLOGY

Malvandi, A., & Ganji, D. D. (2016). Mixed convection of alumina–water nanofluid inside a concentric annulus considering nanoparticle migration. Particuology, 24, 113-122. https://doi.org/10.1016/j.partic.2014.12.017

Mixed convection of alumina–water nanofluid inside a concentric annulus considering nanoparticle migration

A. Malvandi ^a^*, D.D. Ganji ^b

a Department of Mechanical Engineering, Neyshabur Branch, Islamic Azad University, Neyshabur, Iran
b Mechanical Engineering Department, Babol University of Technology, Babol, Iran

10.1016/j.partic.2014.12.017

Volume 24, February 2016, Pages 113-122

Received 24 November 2014, Revised 23 December 2014, Accepted 27 December 2014, Available online 15 July 2015, Version of Record 21 January 2016.

E-mail: amirmalvandi@aut.ac.ir

Highlights

• Mixed convection of alumina–water nanofluid inside a vertical annulus was investigated.

• Modified two-component heterogeneous model for the nanofluid was used.

• Asymmetric heating at the walls changes the direction of nanoparticle migration.

• The efficacy of using nanofluids is always reduced for heat flux ratio ɛ > 1.

• Using smaller nanoparticles enhances the efficacy of using nanofluids.

Abstract

A theoretical investigation was conducted of laminar fully developed mixed convection of alumina–water nanofluid through a vertical annulus, to improve its heating/cooling performance. We focused on controlling the nanoparticle migration and studying how it affected the heat transfer rate and pressure drop. Because the nanoparticles have very small dimensions, we only considered Brownian motion and thermophoretic diffusivity as the main causes of nanoparticle migration. Because thermophoresis is very sensitive to temperature gradients, we imposed various temperature gradients using asymmetric heating. Considering hydrodynamically and thermally fully developed flow, the governing equations were reduced to two-point ordinary boundary value differential equations and were solved numerically. The imposed thermal asymmetry changed the direction of nanoparticle migration and distorted the velocity, temperature, and nanoparticle concentration profiles. Moreover, we found optimum values for the radius ratio (ζ) and heat flux ratio (ɛ); with these optimum values, the nanofluid enhanced the efficacy of the system.

Graphical abstract

Keywords

Nanofluid; Nanoparticle migration; Mixed convection; Asymmetry heating; Modified Buongiorno's model

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