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Unformatted text preview: Advanced Powder Technol. , Vol. 18, No. 6, pp. 813–824 (2007) VSP and Society of Powder Technology, Japan 2007. Also available online - www.brill.nl/apt Invited paper Forced convective heat transfer of nanofluids YULONG DING 1 , ∗ , HAISHENG CHEN 1 , 2 , YURONG HE 1 , ALEXEI LAPKIN 3 , MAHBOUBEH YEGANEH 4 , LIDIJA ŠILLER 4 and YURIY V. BUTENKO 4 1 Institute of Particle Science and Engineering, University of Leeds, Leeds LS2 9JT, UK 2 Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing, China 3 Department of Chemical Engineering, University of Bath, Bath, UK 4 School of Chemical Engineering and Advanced Materials, University of Newcastle, Newcastle upon Tyne, UK Received 8 April 2007; accepted 14 June 2007 Abstract —Forced convective heat transfer is experimentally investigated using aqueous and ethylene glycol-based spherical titania nanofluids, and aqueous-based titanate nanotubes, carbon nanotubes and nano-diamond nanofluids. These nanofluids are formulated from dry nanoparticles and pure base liquids to eliminate complications due to unknown solution chemistry. All the formulated nanofluids show a higher effective thermal conductivity than that predicted by the conventional theories. Except for the ethylene glycol-based titania nanofluids, all other nanofluids are found to be non-Newtonian. For aqueous-based titania and carbon and titanate nanotube nanofluids, the convective heat transfer coefficient enhancement exceeds, by a large margin, the extent of the thermal conduction enhancement. However, deterioration of the convective heat transfer is observed for ethylene glycol-based titania nanofluids at low Reynolds numbers and aqueous-based nano-diamond nanofluids. Possible mechanisms for the observed controversy are discussed from both microscopic and macroscopic viewpoints. The competing effects of particle migration on the thermal boundary layer thickness and that on the effective thermal conductivity are suggested to be responsible for the experimental observations. Keywords : Nanofluids; convective heat transfer; thermal conductivity; rheology; mechanisms; heat transfer enhancement. 1. INTRODUCTION This work is concerned with forced convective heat transfer of nanofluids—heat transfer between a forced flowing nanofluid through a confined region and the confining walls. Forced convective heat transfer plays a significant role in almost all industrial sectors. Examples include cooling of microelectronics, process ∗ To whom correspondence should be addressed. E-mail: firstname.lastname@example.org 814 Y. Ding et al. intensification in the chemical industry, heat exchange/waste heat recovery in power plants and cooling of car engines, to name but a few....
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