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Numerical Simulation of Natural Convection of a Nanofluid in an Inclined Heated Enclosure Using Two-Phase Lattice Boltzmann Method: Accurate Effects of Thermophoresis and Brownian Forces.

Ahmed M, Eslamian M - Nanoscale Res Lett (2015)

Bottom Line: The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and the base fluid are included in the simulation.The effect of thermophoresis is considered using an accurate and quantitative formula proposed by the authors.Some of the existing results on natural convection are erroneous due to using wrong thermophoresis models or simply ignoring the effect.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Assiut University, Assiut, 71516, Egypt.

ABSTRACT
Laminar natural convection in differentially heated (β = 0°, where β is the inclination angle), inclined (β = 30° and 60°), and bottom-heated (β = 90°) square enclosures filled with a nanofluid is investigated, using a two-phase lattice Boltzmann simulation approach. The effects of the inclination angle on Nu number and convection heat transfer coefficient are studied. The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and the base fluid are included in the simulation. The effect of thermophoresis is considered using an accurate and quantitative formula proposed by the authors. Some of the existing results on natural convection are erroneous due to using wrong thermophoresis models or simply ignoring the effect. Here we show that thermophoresis has a considerable effect on heat transfer augmentation in laminar natural convection. Our non-homogenous modeling approach shows that heat transfer in nanofluids is a function of the inclination angle and Ra number. It also reveals some details of flow behavior which cannot be captured by single-phase models. The minimum heat transfer rate is associated with β = 90° (bottom-heated) and the maximum heat transfer rate occurs in an inclination angle which varies with the Ra number.

No MeSH data available.


Related in: MedlinePlus

Variation of the average Nu number along the hot wall of the enclosure versus nanoparticle volume fraction at aβ = 0°, bβ = 30°, cβ = 60°, and dβ = 90°
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Fig6: Variation of the average Nu number along the hot wall of the enclosure versus nanoparticle volume fraction at aβ = 0°, bβ = 30°, cβ = 60°, and dβ = 90°

Mentions: In Fig. 6, the variation of the average Nu number on the hot wall [5] versus the particle volume fraction is displayed for various inclination angles and Ra numbers. The Nu number is significantly larger at Ra = 106 compared to that at Ra = 104, due to the development of a convective flow at Ra = 106. Inclusion of nanoparticles has a higher effect on heat transfer enhancement at Ra = 106, where a sufficiently strong convective flow has developed in the cell. At Ra = 104, heat transfer is more dominated by conduction and the addition of nanoparticles has a weaker effect on heat transfer augmentation. In most cases, the Nu number increases linearly with an increase in the particle volume fraction. Note that the effect of considering thermophoresis in the simulations is also shown on the plots, where a significant heat transfer augmentation is observed at Ra = 106, whereas at Ra = 104, this effect is negated. Effect of the inclination angle on thermophoresis contribution can be also inferred. Thermophoresis has a larger contribution in heat transfer enhancement at β = 0 (differentially heated enclosure), where the relative percentage of increase in Nu number is 5 % at particle volume concentration of 5 %.Fig. 6


Numerical Simulation of Natural Convection of a Nanofluid in an Inclined Heated Enclosure Using Two-Phase Lattice Boltzmann Method: Accurate Effects of Thermophoresis and Brownian Forces.

Ahmed M, Eslamian M - Nanoscale Res Lett (2015)

Variation of the average Nu number along the hot wall of the enclosure versus nanoparticle volume fraction at aβ = 0°, bβ = 30°, cβ = 60°, and dβ = 90°
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508308&req=5

Fig6: Variation of the average Nu number along the hot wall of the enclosure versus nanoparticle volume fraction at aβ = 0°, bβ = 30°, cβ = 60°, and dβ = 90°
Mentions: In Fig. 6, the variation of the average Nu number on the hot wall [5] versus the particle volume fraction is displayed for various inclination angles and Ra numbers. The Nu number is significantly larger at Ra = 106 compared to that at Ra = 104, due to the development of a convective flow at Ra = 106. Inclusion of nanoparticles has a higher effect on heat transfer enhancement at Ra = 106, where a sufficiently strong convective flow has developed in the cell. At Ra = 104, heat transfer is more dominated by conduction and the addition of nanoparticles has a weaker effect on heat transfer augmentation. In most cases, the Nu number increases linearly with an increase in the particle volume fraction. Note that the effect of considering thermophoresis in the simulations is also shown on the plots, where a significant heat transfer augmentation is observed at Ra = 106, whereas at Ra = 104, this effect is negated. Effect of the inclination angle on thermophoresis contribution can be also inferred. Thermophoresis has a larger contribution in heat transfer enhancement at β = 0 (differentially heated enclosure), where the relative percentage of increase in Nu number is 5 % at particle volume concentration of 5 %.Fig. 6

Bottom Line: The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and the base fluid are included in the simulation.The effect of thermophoresis is considered using an accurate and quantitative formula proposed by the authors.Some of the existing results on natural convection are erroneous due to using wrong thermophoresis models or simply ignoring the effect.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Assiut University, Assiut, 71516, Egypt.

ABSTRACT
Laminar natural convection in differentially heated (β = 0°, where β is the inclination angle), inclined (β = 30° and 60°), and bottom-heated (β = 90°) square enclosures filled with a nanofluid is investigated, using a two-phase lattice Boltzmann simulation approach. The effects of the inclination angle on Nu number and convection heat transfer coefficient are studied. The effects of thermophoresis and Brownian forces which create a relative drift or slip velocity between the particles and the base fluid are included in the simulation. The effect of thermophoresis is considered using an accurate and quantitative formula proposed by the authors. Some of the existing results on natural convection are erroneous due to using wrong thermophoresis models or simply ignoring the effect. Here we show that thermophoresis has a considerable effect on heat transfer augmentation in laminar natural convection. Our non-homogenous modeling approach shows that heat transfer in nanofluids is a function of the inclination angle and Ra number. It also reveals some details of flow behavior which cannot be captured by single-phase models. The minimum heat transfer rate is associated with β = 90° (bottom-heated) and the maximum heat transfer rate occurs in an inclination angle which varies with the Ra number.

No MeSH data available.


Related in: MedlinePlus