Numerical analysis of transient laminar forced convection of nanofluids in circular ducts

• Published in: Heat and mass transfer 2013-10, Vol.49 (10), p.1405-1417
• Main Authors: Sert, İsmail Ozan, Sezer-Uzol, Nilay, Kakaç, Sadık
• Format: Article
• Language: English
• Subjects: Engineering; Engineering Thermodynamics; Heat and Mass Transfer; Industrial Chemistry/Chemical Engineering; Original; Thermodynamics
• ISSN: 0947-7411; 1432-1181
• DOI: 10.1007/s00231-013-1184-1

In this study, forced convection heat transfer characteristics of nanofluids are investigated by numerical analysis of incompressible transient laminar flow in a circular duct under step change in wall temperature and wall heat flux. The thermal responses of the system are obtained by solving energy equation under both transient and steady-state conditions for hydro-dynamically fully-developed flow. In the analyses, temperature dependent thermo-physical properties are also considered. In the numerical analysis, Al 2 O 3 /water nanofluid is assumed as a homogenous single-phase fluid. For the effective thermal conductivity of nanofluids, Hamilton–Crosser model is used together with a model for Brownian motion in the analysis which takes the effects of temperature and the particle diameter into account. Temperature distributions across the tube for a step jump of wall temperature and also wall heat flux are obtained for various times during the transient calculations at a given location for a constant value of Peclet number and a particle diameter. Variations of thermal conductivity in turn, heat transfer enhancement is obtained at various times as a function of nanoparticle volume fractions, at a given nanoparticle diameter and Peclet number. The results are given under transient and steady-state conditions; steady-state conditions are obtained at larger times and enhancements are found by comparison to the base fluid heat transfer coefficient under the same conditions.