Thermal conductivity and particle agglomeration in alumina nanofluids: Experiment and theory

The paper presents the results of systematic measurements of the thermal conductivity coefficient of nanofluids at room temperature. In total, more than fifty various nanofluids based on water, ethylene glycol, and engine oil containing particles of SiO2, Al2O3, TiO2, ZrO2, CuO, and diamond were studied. The nanoparticles volume concentration ranged from 0.25 to 8% and the particles size ranged from 10 to 150 nm. It is shown that the thermal conductivity of nanofluids is not described by the classical theories (Maxwell's and so forth). The nanofluid thermal conductivity coefficient is a complicated function not only of the particle concentration, but also the particles size, their material, and type of base fluid. Measured thermal conductivity coefficients almost always exceed the values calculated by the Maxwell's formula, though nanofluids with sufficiently small particles may have thermal conductivity coefficients even lower than those predicted by the Maxwell theory. However, in all cases, the nanofluid thermal conductivity coefficient enhances with increasing particle size. It is convincingly shown that there is no direct correlation between the thermal conductivity of the nanoparticle material and the thermal conductivity of nanofluid containing these particles. The base liquid also significantly influences the effective thermal conductivity of the nanofluid. It has been confirmed that the lower the thermal conductivity of the base fluid, the higher the relative thermal conductivity coefficient of the nanofluid.

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“…Similar data for nanofluids with particles of Al2O3, SiC and Au were reported in [15][16][17][18][19].…”

Section: Introductionsupporting

confidence: 74%

Thermal conductivity measurements of nanofluids

Pryazhnikov

Минаков

Rudyak

et al. 2017

International Journal of Heat and Mass Transfer

214

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“…Figs. 14 and 15 indicated the experimental measurements of the thermal conductivity that compared with the thermal conductivity models of many researchers such as Wasp model [19], Hamilton and Crosser [20], Maxwell model [21] and Timo Feeva et al model [22]. These results showed a good agreement between the Wasp model.…”

Section: Measurement Of the Nanofluid Thermal Propertiessupporting

confidence: 72%

Experimental Analysis of Heat Transfer Enhancement and Flow with Cu, TiO2 Ethylene Glycol Distilled Water Nanofluid in Spiral Coil Heat

Sultan

2017

Tikrit j. eng. sci.

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Nanofluid ethylene glycol enhancement metallic nano metallic A R T I C L E I N F O A B S T R A C TThis experimental investigation was performed to improve heat transfer in the heat exchanger (tube of shell and helically coiled (using nanoparticles for turbulent parallel flow and counter flow of distilled water (Dw) and ethylene glycol (EG) fluids. Six types of nanofluids have been used namely: copper -distilled water, copper -distilled water and ethylene glycol, copper -ethylene glycol, titanium oxide -distilled water, titanium oxide -distilled water and ethylene glycol, titanium oxide -ethylene glycol with 0.5%,1%,2%,3% and 5% volume concentration as well as the range of Reynolds number are 4000 -15000. The experimental results reveal that an increase in coefficient of heat transfer of 50.2 % to Cu -Dw, 41.5% to Cu -( EG + Dw ), 32.12 % for Cu -EG , 36.5% for TiO2 -Dw, 30.2 % to TiO2 -( EG + Dw) and 25.5%, to TiO2 -EG . The strong nanoconvection currents and good mixing caused by the presence of Cu and TiO2 nanoparticles. The metal nanofluids give more improvement than oxide nanofluids. The shear stress of nanofluids increases with concentration of nanoparticles in the case of parallel and counter flow. The effect of flow direction is insignificant on coefficient of overall heat transfer and the nanofluids behave as the Newtonian fluid for 0.5%,1%,2%,3% and 5%. Good assent between the practical data and analytical prediction to nanofluids friction factor which means the nanofluid endure pump power with no penalty. This study reveals that the thermal performance from nanofluid Cu -Dw is higher than Cu -(EG + Dw) and Cu -EG due to higher thermal conductivity for the copper and distilled water compared with ethylene glycol.

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“…Other researchers reported that the thermal conductivity enhancement was decreased as concentration increased from 6% to 10% [2]. The same phenomena was observed also when the thermal conductivity was increased as concentration increased from 2% to 10% [3], Al2O3 nanoparticles even though the particle size was almost the same in both the cases. The great disadvantage of larger nanoparticles is that suspensions tend to become unstable.…”

Section: Introductionsupporting

confidence: 63%