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Single Phase Convective Heat Transfer with Nanofluids: An Experimental Approach
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
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 [en]
nanofluid, convective heat transfer, thermal conductivity, viscosity, heat transfer coefficient, performance, pumping power, Reynolds number, shelf stability
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-159199ISBN: 987-91-7595-414-1 OAI: oai:DiVA.org:kth-159199DiVA: diva2:783166
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
List of papers
1. Screening Single Phase Laminar Convective Heat Transfer of Nanofluids in a Micro-tube
Open this publication in new window or tab >>Screening Single Phase Laminar Convective Heat Transfer of Nanofluids in a Micro-tube
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2012 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 395, 012036- p.Article in journal (Refereed) Published
Abstract [en]

Nano scale solid particles dispersed in base fluids are a new class of engineered colloidal solutions called nanofluids. Several studies reported enhancement of heat transfer by using nanofluids. This article reports convective single-phase heat transfer coefficients in an open 30 cm long, 0.50 mm internal diameter stainless steel test section. The setup is used for screening single phase laminar convective heat transfer with water and three different nanofluids: water based Al2O3, ZrO2, and TiO2 (all with 9 wt% of particles). A syringe pump with adjustable pumping speed is used to inject fluids into the test section. Thirteen T-type thermocouples are attached on the outer surface of the test section to record the local wall temperatures. Furthermore, two T-type thermocouples are used to measure inlet and outlet fluid temperatures. A DC power supply is used to heat up the test section and a differential pressure transducer is used to measure the pressure drop across the tube. Furthermore, the effective thermal conductivities of these nanofluids are measured using the Transient Plane Source (TPS) method at a temperature range of 20 - 50 degrees C. The experimental average values of heat transfer coefficients for nanofluids are compared with water. Enhancement in heat transfer of nanofluids is observed only when compared at constant Reynolds number (Due to higher viscosity for nanofluids, higher velocity or mass flow rate is required for nanofluids to reach the same Reynolds number). The other methods of comparison: equal mass flow rate, volume flow rate, pressure drop and pumping power did not show any augmentation of the heat transfer coefficient for the tested nanofluids compared to water.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-116748 (URN)10.1088/1742-6596/395/1/012036 (DOI)000312264800036 ()2-s2.0-84875036410 (Scopus ID)
Conference
6th European Thermal Sciences Conference (Eurotherm), SEP 04-07, 2012, Poitiers, France
Note

QC 20130128

Available from: 2013-01-28 Created: 2013-01-25 Last updated: 2017-06-13Bibliographically approved
2. Measurement of temperature–dependent viscosity of nanofluids and its effect on pumping power in cooling systems
Open this publication in new window or tab >>Measurement of temperature–dependent viscosity of nanofluids and its effect on pumping power in cooling systems
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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.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-159198 (URN)
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
3. Accurate basis of comparison for convective heat transfer in nanofluids
Open this publication in new window or tab >>Accurate basis of comparison for convective heat transfer in nanofluids
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2014 (English)In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 52, 1-7 p.Article in journal (Refereed) Published
Abstract [en]

Thermal conductivity and viscosity of alumina (Al2O3), zirconia (ZrO2), and titania (TiO2) nanofluids (NFs) were measured at 20°C. All the NF systems were water based and contained 9wt.% solid particles. Additionally, the heat transfer coefficients for these NFs were measured in a straight tube of 1.5m length and 3.7mm inner diameter. Based on the results, it can be stated that classical correlations, such as Shah and Gnielinski, for laminar and turbulent flow respectively, can be employed to predict convective heat transfer coefficients in NFs, if the accurate thermophysical properties are used in the calculations. Convective heat transfer coefficients for NFs were also compared with those of the base fluids using two different bases for the comparison, with contradictory results: while compared at equal Reynolds number, the heat transfer coefficients increased by 8-51%, whereas compared at equal pumping power the heat transfer coefficients decreased by 17-63%. As NFs have higher viscosity than the base fluids, equal Reynolds number requires higher volumetric flow, hence higher pumping power for the NFs. It is therefore strongly suggested that heat transfer results should be compared at equal pumping power and not at equal Reynolds number.

Keyword
Comparison, Convective, Heat transfer, Laminar, Nanofluid, Pumping power, Turbulent
National Category
Materials Engineering Energy Engineering
Identifiers
urn:nbn:se:kth:diva-142775 (URN)10.1016/j.icheatmasstransfer.2014.01.002 (DOI)000334484100001 ()2-s2.0-84893382995 (Scopus ID)
Note

QC 20140312

Available from: 2014-03-12 Created: 2014-03-12 Last updated: 2017-12-05Bibliographically approved
4. Cooling performance of nanofluids in a small diameter tube
Open this publication in new window or tab >>Cooling performance of nanofluids in a small diameter tube
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2013 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 49, 114-122 p.Article in journal (Refereed) Published
Abstract [en]

This article reports convective single-phase heat transfer performance in laminar flow for some selected nanofluids (NFs) in an open small diameter test section. A 0.50 mm inner diameter, 30 cm long stainless steel test section was used for screening single phase laminar convective heat transfer with water and five different water based NFs. Tested NFs were; Al2O3 (two types), TiO2 (two types) and CeO2 (one type), all 9 wt.% particle concentration. The effective thermal conductivity of the NFs were measured with Transient Plane Source (TPS) method and viscosity were measured with a rotating coaxial cylindrical viscometer. The obtained experimental results for thermal conductivity were in good agreement with the predicted values from Maxwell equation. The local Shah correlation, which is conventionally used for predicting convective heat transfer in laminar flow in Newtonian fluids with constant heat flux boundary condition, was shown to be valid for NFs. Moreover, the Darcy correlation was used to predict the friction factor for the NFs as well as for water. Enhancement in heat transfer for NFs was observed, when compared at equal Reynolds number, as a result of higher velocity or mass flow rate of the NFs at any given Reynolds number due to higher viscosity for NFs. However, when compared at equal pumping power no or only minor enhancement was observed.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Nanofluids, Thermal conductivity, Viscosity, Heat transfer coefficient, Tube, Cooling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-125539 (URN)10.1016/j.expthermflusci.2013.04.009 (DOI)000321404800012 ()2-s2.0-84878896950 (Scopus ID)
Note

QC 20130813

Available from: 2013-08-13 Created: 2013-08-09 Last updated: 2017-06-13Bibliographically approved
5. The effect of nanoparticles on laminar heat transfer in a horizontal tube
Open this publication in new window or tab >>The effect of nanoparticles on laminar heat transfer in a horizontal tube
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2014 (English)In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 69, 77-91 p.Article in journal (Refereed) Published
Abstract [en]

Heat transfer coefficient in laminar flow of water-based alumina, titania and carbon nanotube nanofluids in a straight pipe with constant heat flux at the wall have been investigated independently by two universities. The nanoparticles affect the thermo-physical properties of the suspensions, however, nanopartides presence and movement due to Brownian diffusion and thermophoresis seemed to have insignificant effect on heat transfer coefficient. The Nusselt number of all investigated nanofluids followed standard heat transfer correlations developed for liquids within +/- 10% suggesting that all investigated nanofluids can be treated as homogenous fluids. Different methods of comparison between heat transfer coefficient in nanofluids and base fluid are also critically discussed.

Keyword
Nanofluid, Heat transfer coefficient, Laminar flow
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-141055 (URN)10.1016/j.ijheatmasstransfer.2013.10.003 (DOI)000329552900009 ()2-s2.0-84887105815 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, NMP-2008-1.2-1
Note

QC 20140212

Available from: 2014-02-12 Created: 2014-02-07 Last updated: 2017-12-06Bibliographically approved
6. Experimental study on convective heat transfer of nanofluids in turbulent flow: Methods of comparison of their performance
Open this publication in new window or tab >>Experimental study on convective heat transfer of nanofluids in turbulent flow: Methods of comparison of their performance
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2014 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, 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.

Keyword
Nanofluids, Convective heat transfer, Turbulent, Circular tube, Al2O3, TiO2, Pumping power
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-150912 (URN)10.1016/j.expthermflusci.2014.05.019 (DOI)000340340300041 ()2-s2.0-84903149536 (Scopus ID)
Note

QC 20140915

Available from: 2014-09-15 Created: 2014-09-11 Last updated: 2017-12-05Bibliographically approved
7. Combined effect of physical properties and convective heat transfer coefficient of nanofluids on their cooling efficiency
Open this publication in new window or tab >>Combined effect of physical properties and convective heat transfer coefficient of nanofluids on their cooling efficiency
Show others...
2015 (English)In: International Communications in Heat and Mass Transfer, ISSN 0735-1933, E-ISSN 1879-0178, Vol. 68, 32-42 p.Article in journal (Refereed) Published
Abstract [en]

The advantages of using Al2O3, TiO2, SiO2 and CeO2 nanofluids as coolants have been investigated by analysing the combined effect of nanoparticles on thermophysical properties and heat transfer coefficient. The thermal conductivity and viscosity of these nanofluids were measured at two leading European universities to ensure the accuracy of the results. The thermal conductivity of nanofluids agreed with the prediction of the Maxwell model within +/- 10% even at elevated temperature of 50 oC indicating that the Brownian motion of nanoparticles does not affect thermal conductivity of nanofluids. The viscosity of nanofluids is well correlated by modified Krieger-Dougherty model providing that the effect of nanoparticles aggregation is taken into account. It was found that at the same Reynolds number the advantage of using a nanofluid increases with increasing nanofluid viscosity which is counterintuitive. At the same pumping power nanofluids do not offer any advantage in terms of cooling efficiency over base fluids since the increase in viscosity outweighs the enhancement of thermal conductivity.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-159213 (URN)10.1016/j.icheatmasstransfer.2015.08.011 (DOI)000365057200006 ()2-s2.0-84941108099 (Scopus ID)
Note

Updated from "Manuscript" to "Article". QC 20150907

Available from: 2015-01-26 Created: 2015-01-26 Last updated: 2017-12-05Bibliographically approved
8. Shelf stability of nanofluids and its effect on thermal conductivity and viscosity
Open this publication in new window or tab >>Shelf stability of nanofluids and its effect on thermal conductivity and viscosity
Show others...
2013 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 24, no 10, 105301- p.Article in journal (Refereed) Published
Abstract [en]

This study proposes a method and apparatus to estimate shelf stability of nanofluids. Nanofluids are fabricated by dispersion of solid nanoparticles in base fluids, and shelf stability is a key issue for many practical applications of these fluids. In this study, shelf stability is evaluated by measuring the weight of settled solid particles on a suspended tray in a colloid versus time and correlated with the performance change of some nanofluid systems. The effects of solid particle concentration and bath sonication time were investigated for selected nanofluids. The results show the applicability of this simple method and the apparatus to evaluate nanofluid shelf stability. Furthermore, it shows that Stokes' law is not valid for determining the settling time of the tested nanoparticles probably due to their complicated shape and presence of surface modifiers. The effect of shelf stability on thermal conductivity and viscosity was illustrated for some nanofluids. Experimental results show that water-based Al2O3 nanofluids have quite good shelf stability and can be good candidates for industrial applications.

Keyword
Al 2O3, balance, CeO2, china clay, Nanofluid, sedimentation, shelf stability, sonication
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-133188 (URN)10.1088/0957-0233/24/10/105301 (DOI)000324621900032 ()2-s2.0-84884851197 (Scopus ID)
Note

QC 20131028

Available from: 2013-10-28 Created: 2013-10-28 Last updated: 2017-12-06Bibliographically approved

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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
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  • de-DE
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  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
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