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Experimental study on convective heat transfer of nanofluids in turbulent flow: Methods of comparison of their performance
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
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2014 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, Vol. 57, 378-387 p.Article in journal (Refereed) Published
Abstract [en]

Turbulent convective heat transfer coefficients of 9 wt% Al2O3/water and TiO2/water nanofluids inside a circular tube were investigated independently at the Royal Institute of Technology, KTH (Sweden) and at University of Birmingham (UK). The experimental data from both laboratories agreed very well and clearly show that Nusselt numbers are well correlated by the equations developed for single phase fluids with the thermophysical properties of nanofluid. The heat transfer coefficients of nanofluids can be compared with those of the base fluids at the same Reynolds number or at the same pumping power. As the same Reynolds number requires higher flow rate of nanofluids therefore such comparison shows up to 15% increase in heat transfer coefficient. However, at equal pumping power, the heat transfer coefficient of Al2O3 nanofluid was practically the same as that of water while that of TiO2 was about 10% lower. Comparing performance at equal Reynolds number is clearly misleading since the heat transfer coefficient can always be increased by increased pumping power, accordingly, the comparison between the fluids should be done at equal pumping power.

Place, publisher, year, edition, pages
2014. Vol. 57, 378-387 p.
Keyword [en]
Nanofluids, Convective heat transfer, Turbulent, Circular tube, Al2O3, TiO2, Pumping power
National Category
Energy Engineering
URN: urn:nbn:se:kth:diva-150912DOI: 10.1016/j.expthermflusci.2014.05.019ISI: 000340340300041ScopusID: 2-s2.0-84903149536OAI: diva2:746736

QC 20140915

Available from: 2014-09-15 Created: 2014-09-11 Last updated: 2015-01-26Bibliographically approved
In thesis
1. Single Phase Convective Heat Transfer with Nanofluids: An Experimental Approach
Open this publication in new window or tab >>Single Phase Convective Heat Transfer with Nanofluids: An Experimental Approach
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanofluids (NFs) are engineered colloids of nanoparticles (NPs) dispersed homogenously within base fluids (BFs). Due to the presence of NPs, the thermophysical and transport properties of BFs are subject to change. Existing technologies for cooling electronics seem to be insufficient and NFs, as reported in several studies, might offer a better alternative to liquid cooling. The main purpose of this study, by choosing a critical approach to existing knowledge in the literature, is to investigate experimentally the potential for replacing BFs with NFs in single–phase flow. Several NFs (mainly water based metal oxide NFs) were synthesised, and different experiments (including thermal conductivity, viscosity, heat transfer coefficient, and shelf stability) were performed.

The thermal conductivity and the viscosity of several NFs were measured at both near room and elevated temperatures; the results are reported and compared with some correlations. It is shown that the Maxwell model for thermal conductivity and the modified Krieger–Dougherty model for viscosity can be used to predict these properties of NFs within ±10% error, even at elevated temperatures.

A screening setup, including a test section with d = 0.5 mm and L = 30 cm, was designed for measuring the heat transfer performance of NFs in laminar flow. In addition a closed–loop setup with a 3.7 mm inner diameter and 1.5 m length test section was also designed to measure the heat transfer coefficients in both laminar and turbulent flow with higher accuracy. Based on the results, classical correlations for predicting Nusselt number and friction factor in a straight tube are still valid for NFs within ± (10 – 20)% error provided that the correct thermophysical properties are used for NFs.

Different methods of comparing cooling performance of NFs to BFs are then investigated. Comparison at equal Reynolds number, the most popular method in the literature, is demonstrated both experimentally and analytically to be misleading. However, if the most correct criterion (at equal pumping power) is chosen, a small advantage for some NFs over their BFs should be expected only under laminar flow. The investigation concludes with the proposition of a unique method and apparatus to estimate the shelf stability of NFs.

Abstract [sv]

Nanofluider (NF) kallas suspensioner av nanopartiklar (NP) i en vätska (base fluid, BF). Tillsatsen av nanopartiklar leder till förändring av vätskans termodynamiska- och transport-egenskaper vilket eventuellt kan utnyttjas för att anpassa egenskaperna efter speciella behov.

Befintliga teknologier för kylning av elektronik tenderar att vara otillräckliga och nanofluider kan, som föreslagits i olika studier, ge en möjlighet att åstadkomma effektivare vätskekylning än dagens kylmedier. Huvudsyftet med denna studie har varit att kritiskt granska tidigare publicerad information om nanofluider samt att genom nya tester av många olika nanofluider undersöka potentialen för att ersätta vanligt förekommande kylvätskor med nanofluider i tillämpningar utan fasändring. Ett stort antal nanofluider, huvudsakligen vattenbaserade metall-oxid nanofluider, karakteriserades genom bestämning av värmeledningstal, viskositet, värmeövergångstal vid rörströmning och möjlig lagringstid. De experimentella resultaten analyseras i detalj och jämförs med korrelationer från litteraturen.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. x, 116 p.
TRITA-REFR, ISSN 1102-0245 ; 15:01
nanofluid, convective heat transfer, thermal conductivity, viscosity, heat transfer coefficient, performance, pumping power, Reynolds number, shelf stability
National Category
Energy Engineering
urn:nbn:se:kth:diva-159199 (URN)987-91-7595-414-1 (ISBN)
Public defence
2015-02-05, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20150126

Available from: 2015-01-26 Created: 2015-01-23 Last updated: 2015-01-27Bibliographically approved

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