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Author:Mikkola, Valtteri
Title:Impact of concentration, particle size and thermal conductivity on effective convective heat transfer of nanofluids
Konsentraation, partikkelikoon ja lämmönjohtavuuden vaikutus nanonesteiden efektiiviseen konvektiolämmönsiirtoon
Publication type:Master's thesis
Publication year:2015
Pages:83      Language:   eng
Department/School:Insinööritieteiden korkeakoulu
Main subject:Energiatekniikka   (K3007)
Supervisor:Vuorinen, Ville
Instructor:Seppälä, Ari ; Puupponen, Salla
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201509184357
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  6953   | Archive
Keywords:nanofluid
convective heat transfer
heat exchanger
viscosity
pressure loss
pumping power
nanoneste
konvektiolämmönsiirto
lämmönsiirrin
painehäviö
pumppausteho
konsentraatio
partikkelikoko
lämmönjohtavuus
viskositeetti
Abstract (eng):Nanofluids are a modern type of heat transfer fluids, in which typically solid nano-sized particles (d < 100 nm) are dispersed in conventional heat transfer fluid, such as water or oils.
In earlier studies, nanofluids have shown anomalous enhancement of convective heat transfer that cannot be explained with conventional correlations.
Water-based nanofluids with volume fraction of only a few percents have typically yielded tens of percents higher Nusselt numbers than water when compared with equal Reynolds numbers.
In addition, several studies suggest that the addition of nanoparticles enhances convective heat transfer without significant penalty in pressure losses.

In this Master's Thesis, impacts of concentration, particle size and thermal conductivity of particle material on convective heat transfer of nanofluids are experimentally examined.
For this purpose, water-based nanofluids containing SiO2, micelle, polystyrene or Al2O3 particles were prepared and measured with an annular tube heat exchanger.
The heat transfer measurements also included the pressure losses in order to study the suitability of nanofluids for practical heat transfer applications.
The fluids were characterized thoroughly for the sake of an accurate analysis: viscosities, thermal conductivities, densities, particle sizes and zeta potentials of the samples were measured.
Furthermore, analysis methods were developed in order to minimize the experimental errors.In the experimental series, all nanofluids performed as Gnielinski correlation predicts and thus, no anomalous enhancement was observed.
The nanofluids reached slightly higher Nusselt numbers than water when compared on the basis of equal Reynolds numbers, but no difference was observed when the effect of Prandtl number was taken into account.
In comparison on the basis of equal pumping powers, the nanofluids showed equal or poorer performance than water.
Increasing particle concentration was observed to lower the heat transfer performance of the fluids in all cases.
However, the magnitude of this deteriorating effect was smaller for nanofluids with smaller particle size indicating that small particle size is beneficial for heat transfer of nanofluids.
The thermal conductivity of particle material did not have a notable impact on the convection heat transfer with the studied relatively small particle concentrations (=<1%).

Based on the results of this work, the performance of the nanofluids studied herein do not seem suitable for practical forced convection applications.
However, enhancing thermal conductivities of fluids via the addition of nanoparticles might still offer potential for improved convective heat transfer, since behavior of nanofluids was observed to follow conventional correlations.
ED:2015-09-27
INSSI record number: 52074
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