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Measurement of temperature–dependent viscosity of nanofluids and its effect on pumping power in cooling systems
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.ORCID iD: 0000-0001-5380-975X
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
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2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Nanofluids are engineered colloids of nanoparticlesdispersed homogenously in a base fluid, which theirthermophysical properties are changed by adding solidnanoparticles. Among the characteristic parameters,viscosity is one of the most important, as it directly affectsthe pumping power in cooling systems. In this study, theviscosity of water based Al2O3, ZrO2, and TiO2 (with 9wt%for all) nanofluids was measured and its impact on pressuredrop in a simple tubular pipe was estimated for bothlaminar and turbulent flow by classical correlations. Theeffect of temperature on the viscosity of these nanofluidswas also studied in the temperature range of 5˚C - 30˚C. Toassess the applicability of the classical correlations, pressuredrops across an open 30cm long, 0.50mm diameterstainless steel test section was measured for water andnanofluids by a differential pressure transducer. Theaverage viscosity increments compared to water in thetemperature range of 5˚C - 30˚C are 105%, 98% and 31% forAl2O3, ZrO2, and TiO2 nanofluids respectively. Moreover, theresults show that the viscosity of nanofluids decreases withthe increase of temperature; however the relative viscosity,which is defined as the viscosity ratio between a nanofluidand its base fluid is constant in 5˚C - 30˚C temperaturerange.

Place, publisher, year, edition, pages
2013.
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-159198OAI: oai:DiVA.org:kth-159198DiVA: diva2:783164
Conference
Proceeding of the 5th International Conference Applied Energy (ICAE), South Africa 2013
Note

QC 20150126

Available from: 2015-01-23 Created: 2015-01-23 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.
Series
TRITA-REFR, ISSN 1102-0245 ; 15:01
Keyword
nanofluid, convective heat transfer, thermal conductivity, viscosity, heat transfer coefficient, performance, pumping power, Reynolds number, shelf stability
National Category
Energy Engineering
Identifiers
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)
Opponent
Supervisors
Note

QC 20150126

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

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Saleemi, MohsinPalm, Björn E.Toprak, Muhammet

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