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Shelf stability of nanofluids and its effect on thermal conductivity and viscosity
KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.ORCID-id: 0000-0001-5380-975X
KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
Visa övriga samt affilieringar
2013 (Engelska)Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 24, nr 10, s. 105301-Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
2013. Vol. 24, nr 10, s. 105301-
Nyckelord [en]
Al 2O3, balance, CeO2, china clay, Nanofluid, sedimentation, shelf stability, sonication
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
URN: urn:nbn:se:kth:diva-133188DOI: 10.1088/0957-0233/24/10/105301ISI: 000324621900032Scopus ID: 2-s2.0-84884851197OAI: oai:DiVA.org:kth-133188DiVA, id: diva2:659895
Anmärkning

QC 20131028

Tillgänglig från: 2013-10-28 Skapad: 2013-10-28 Senast uppdaterad: 2017-12-06Bibliografiskt granskad
Ingår i avhandling
1. Engineering Nanofluids for Heat Transfer Applications
Öppna denna publikation i ny flik eller fönster >>Engineering Nanofluids for Heat Transfer Applications
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Nanofluids (NFs) are nanotechnology-based colloidal dispersion prepared by dispersing nanoparticles (NPs) in conventional liquids, as the base liquid. These advanced fluids have displayed potential to enhance the performance of conventional heat transfer fluids. This work aims at providing an insight to the field of NFs by investigating in detail the fabrication and evaluation of physico-chemical, thermo-physical and heat transfer characteristics of NFs for practical heat transfer applications. However, in order to utilize NFs as heat transfer fluids in real applications there are some challenges to overcome. Therefore, our goal is not only to optimize the thermo-physical properties of NFs with the highest thermal conductivity (TC) and minimal impact of NPs on viscosity, but also on preparing NFs with good stability and the best heat transfer performance. In the first stage, detailed studies were carried out to engineer NFs with good stability and optimal thermo-physical properties. In this work we investigated the most important factors, and the dependence of thermo-physical properties of NFs, including NP composition and concentration, NF stability, surface modifiers, particle size (NP size and particle with micron size), NF preparation method (two-step vs one-step method) and base liquid was studied. We also demonstrated, for the first time, the role of crystal structure, exemplified by alpha- and beta- SiC particles, on thermo-physical properties of NFs. For these purposes several NFs were fabricated using different nanostructured materials and various base liquids by one-step and two-step methods. An optimization procedure was designed to keep a suitable control in order to reach the ultimate aim where several stages were involved to check the desired characteristics of each NF system. Among several NFs systems studied in the first stage evaluation, a particular NF system with 9 wt% concentration, engineered by dispersing SiC NPs with alpha- crystal structure in water/ethylene glycol as based liquid exhibited the optimal thermo-physical properties. This NF was the only case which could pass the all criteria involved in the optimization procedure by exhibiting good stability, TC enhancements of ~20% with only 14% increase in viscosity at 20 oC. Therefore, this engineered NF was considered for next phase evaluation, where heat transfer coefficient (HTC) tests were designed and carried out to evaluate the thermal transport property of the selected alpha- SiC NF. A HTC enhancement of 5.5% at equal pumping power, as realistic comparison criteria, was obtained indicating the capability of this kind of NFs to be used in industrial heat transfer applications. These findings are among the few studies in the literature where the heat transfer characteristics of the NFs were noticeable, reproducible and based on a realistic situation with capability of commercializing as effective heat transfer fluid.  

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2014. s. xiii, 65
Serie
TRITA-ICT/MAP AVH, ISSN 1653-7610 ; 2014:03
Nyckelord
nanofluid, thermal conductivity, viscosity, heat transfer, heat transfer coefficient, HTC, SiC nanoparticles, Cu nanoparticles, mesoporous silica, CNT, microwave synthesis
Nationell ämneskategori
Teknik och teknologier
Forskningsämne
Kemi
Identifikatorer
urn:nbn:se:kth:diva-144217 (URN)978-91-7595-056-3 (ISBN)
Disputation
2014-05-30, Sal D, KTH-Forum, Isafjordagatan 39, Kista, 10:30 (Engelska)
Opponent
Handledare
Projekt
Nanohex
Anmärkning

QC 20140416

Tillgänglig från: 2014-04-16 Skapad: 2014-04-15 Senast uppdaterad: 2014-05-12Bibliografiskt granskad
2. Single Phase Convective Heat Transfer with Nanofluids: An Experimental Approach
Öppna denna publikation i ny flik eller fönster >>Single Phase Convective Heat Transfer with Nanofluids: An Experimental Approach
2015 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2015. s. x, 116
Serie
TRITA-REFR, ISSN 1102-0245 ; 15:01
Nyckelord
nanofluid, convective heat transfer, thermal conductivity, viscosity, heat transfer coefficient, performance, pumping power, Reynolds number, shelf stability
Nationell ämneskategori
Energiteknik
Identifikatorer
urn:nbn:se:kth:diva-159199 (URN)987-91-7595-414-1 (ISBN)
Disputation
2015-02-05, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20150126

Tillgänglig från: 2015-01-26 Skapad: 2015-01-23 Senast uppdaterad: 2015-01-27Bibliografiskt granskad

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