Hydrodynamic Study of Nanofluids in Microchannel
01 Jan 2009-pp 467-473
TL;DR: In this paper, the authors tried to put light on hydrodynamics of nanofluids in microchannels and found that the axial pressure drop is linear thus showing the incompressible behaviour of fluid.
Abstract: Present study tries to put light on hydrodynamics of nanofluids in microchannels. For the present hydrodynamic study, the microchannels of hydraulic diameters of 212 and 301 μm are used. Present study also uses nanofluids in microchannel. To observe the hydrodynamic effect of nanofluids in microchannel, the alumina nanoparticles with sizes 45 nm are chosen with the water as base fluid. The nanofluids with the dilute concentrations 0.25 vol% are used to observe the effect of volume fraction. From the study of base fluid flow in microchannel, it is found that the axial pressure drop is linear thus showing the incompressible behaviour of fluid. For all microchannels, early transition to turbulence was observed. Also for the same Re the pressure drop was higher for smaller channel. However, the usage of nanofluids in these microchannels shows different behavior from normal fluids. The axial pressure drop was again linear thus proving that even though these fluids are different from normal fluids; they follow the behaviour of incompressible Newtonian fluids. Surprisingly, the friction factor was similar for these fluids as compared to base fluids. This can be attributed to dilute concentration of nanofluids, which make them a homogeneous fluid. It suggests that the use of dilute nanofluids in microchannel results in no or little penalty in pressure drop. It also suggests that if nanofluids have to be used as a better coolant, the hydrodynamics and heat transfer characteristics has to be studied as higher concentrations.Copyright © 2009 by ASME
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TL;DR: In this paper, the hydraulic and thermal fields of a 29nm CuO nanoparticle-water nanofluid with various volume fractions, 0.24, 1.03% and 4.5%, were investigated inside a rectangular microchannel heat sink under both laminar and turbulent conditions.
Abstract: This paper presents an experimental investigation of the hydraulic and thermal fields of a 29 nm CuO nanoparticle–water nanofluid with various volume fractions, 0.24%, 1.03% and 4.5% flowing inside a rectangular microchannel heat sink under both laminar and turbulent conditions. The isothermal and heated tests are conducted for Reynolds number up to ≈5000 and to ≈2500, respectively. For a given fluid flow rate experimental results show an increase of the pressure drop and the friction factor with respect to water. This increase can be as high as 70%, 25%, and 0–30%, respectively, for the 4.5%, 1.03%, and 0.24% particle volume fractions. Although the laminar-to-turbulent transition was observed at nearly the same critical Reynolds number Rec ≈ 1000 for water and the tested nanofluids, this value of Rec is clearly lower than that corresponding to a smooth surface microchannel. Results show a slight heat transfer enhancement with respect to water for nanofluids with low particle volume fractions, 0.24% and 1.03%, while for the 4.5% fraction a clear decrease of heat transfer was found. In general, the nanofluid overall energetic performance, defined by the heat transferred/pumping power ratio, remains lower than that of water for a given Reynolds number. This ratio decreases with an augmentation of the particle volume fraction.
119 citations
TL;DR: In this paper, the effect of nanoparticle mass fraction and Re on local convective heat transfer coefficients, and the local Nusselt number was also studied. But the experimental results showed that increased mass fraction of nanoparticles from 0.05 to 0.3 wt% resulted in lower thermal resistances of up to 21%.
Abstract: The utilization of nanofluids of various types as cooling or heating working fluids has given incentive to enhanced heat transfer resulting in even smaller heat exchangers for a given heat duty. In this study, convective heat transfer coefficients and friction factor of copper nanofluids in a cylindrical microchannel heat sink were investigated. Copper nanoparticles with various mass fractions were used for two heat fluxes of 35 and 50 kW/m2. The effect of nanoparticle mass fraction and Re on local convective heat transfer coefficients, and the local Nusselt number was also studied. The experimental results showed that increased mass fraction of nanoparticles from 0.05 to 0.3 wt% resulted in lower thermal resistances of up to 21%. Moreover, the local heat transfer coefficients helped to experimentally determine the thermal entrance length for the microchannel heat sink. The presence of nanoparticles enhanced the entrance Nu up to 43% while the friction factor also increased up to 45.5% compared with that of pure water. Two correlations were finally proposed for the prediction of the Nusselt number and friction factor for the attempted nanofluid in the microchannel which agreed well with the experimental data.
96 citations
TL;DR: In this paper, the convective heat transfer and flow behavior of Graphene-water nanofluids are studied experimentally by focusing on transitional flow, and it is seen that pressure drop increases dramatically in the transition region, and laminar to turbulent transition shifts to lower Reynolds numbers with increasing nanoparticle concentration.
Abstract: The convective heat transfer and flow behavior of graphene-water nanofluids are studied experimentally by focusing on transitional flow. Graphene-water nanofluids with different particle mass fractions (0.025, 0.1 and 0.2%) are produced following two-step method and using PVP as a surfactant. Thermo-physical characterization is performed by measuring viscosity and thermal conductivity of the nanofluids. Convection characteristics are experimentally studied from laminar to turbulent flow regimes. It is seen that pressure drop increases dramatically in the transition region, and laminar to turbulent transition shifts to lower Reynolds numbers with increasing nanoparticle concentration. The transition initiates at a Reynolds number of 2475 for water, while it initiates at 2315 for the nanofluid with 0.2% particle mass fraction. Increase in mean heat transfer coefficient and Nusselt numbers are nearly identical at different Reynolds numbers and axial positions along the test tube in the laminar flow for nanofluids and water due to dominance of conduction enhancement mechanisms on the heat transfer increase in laminar flow. Beyond laminar flow regime, enhancement of Nusselt number is observed indicating that thermophoresis and Brownian motion are more effective heat transfer augmentation mechanisms. The maximum heat transfer enhancement is observed as 36% for a Reynolds number of 3950.
18 citations
Cites result from "Hydrodynamic Study of Nanofluids in..."
...6 that transition starts at smaller Reynolds numbers for nanofluids with higher particle concentrations, in agreement with literature [23,35–38]....
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Posted Content•
TL;DR: In this article, the convective heat transfer and flow behavior of Graphene-water nanofluids are studied experimentally by focusing on transitional flow, and it is seen that pressure drop increases dramatically in the transition region, and laminar to turbulent transition shifts to lower Reynolds numbers with increasing nanoparticle concentration.
Abstract: The convective heat transfer and flow behavior of graphene-water nanofluids are studied experimentally by focusing on transitional flow. Graphene-water nanofluids with different particle mass fractions (0.025, 0.1 and 0.2%) are produced following two-step method and using PVP as a surfactant. Thermo-physical characterization is performed by measuring viscosity and thermal conductivity of the nanofluids. Convection characteristics are experimentally studied from laminar to turbulent flow regimes. It is seen that pressure drop increases dramatically in the transition region, and laminar to turbulent transition shifts to lower Reynolds numbers with increasing nanoparticle concentration. The transition initiates at a Reynolds number of 2475 for water, while it initiates at 2315 for the nanofluid with 0.2% particle mass fraction. Increase in mean heat transfer coefficient and Nusselt numbers are nearly identical at different Reynolds numbers and axial positions along the test tube in the laminar flow for nanofluids and water due to dominance of conduction enhancement mechanisms on the heat transfer increase in laminar flow. Beyond laminar flow regime, enhancement of Nusselt number is observed indicating that thermophoresis and Brownian motion are more effective heat transfer augmentation mechanisms. The maximum heat transfer enhancement is observed as 36% for a Reynolds number of 3950.
16 citations
Dissertation•
22 Nov 2011
4 citations
Cites background from "Hydrodynamic Study of Nanofluids in..."
...[178] and Duangthongsuk and Wongwises [166]), especially for dilute nanofluids....
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...[178] and Duangthongsuk and Wongwises [166] with conventional or mini-scale circular tubes, especially for dilute nanofluids....
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