Numerical study on turbulent heat transfer and pressure drop characteristics of a helically coiled hybrid rectangular-circular tube heat exchanger with Al2O3-water nanofluids

• Published in: Applied thermal engineering 2017-03, Vol.114, p.466-483
• Main Authors: Fsadni, Andrew Michael, Whitty, Justin P.M., Stables, Matthew A., Adeniyi, Akinola A.
• Format: Article
• Language: English
• Subjects: CFD; Coiled tubes; Homogenous model; Nanofluids; Turbulent
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2016.11.181

•7–34% increase in the mean heat transfer coefficient with dispersed nanoparticles.•2.5% increase in the mean heat transfer coefficient with larger coil curvatures.•11–63% increase in the frictional pressure drop with dispersed nanoparticles.•4.7% increase in the frictional pressure drop with larger coil curvatures.•Performance index suggests that nanoparticles will enhance the system performance. In the present study, turbulent Al2O3-water nanofluid flow in helically coiled, hybrid rectangular-circular tubes under constant wall heat flux, was numerically investigated. The heat transfer and pressure drop characteristics were determined as a function of the nanoparticle volume concentration (1–4%) and coil curvature. The system parameters used are typical to those found in contemporary wet central heat systems, with Reynolds numbers and coil curvatures in the range of 10,000–60,000 and 0.032–0.052 respectively. The numerical computations were developed with the widely cited single-phase homogeneous model using ANSYS FLUENT. The model was validated against empirical correlations for the Nusselt number and friction factor of water in coiled tubes and against data for Al2O3-water nanofluid flow in a straight tube. Both the heat transfer coefficient and frictional pressure drop were enhanced with the nanoparticle concentration and curvature. A thermo-hydrodynamic performance index was used to appraise the overall impact, with results suggesting that the nanofluids will enhance the overall system performance. Correlations for the prediction of the Nusselt number and friction factor were fitted to our data with reasonable accuracy.