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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

Nanoparticle volume fraction distribution at steady state for various inclination angles for Ra = 104 and Ra = 106. Pr = 7.02 and ϕ = 0.05
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Fig5: Nanoparticle volume fraction distribution at steady state for various inclination angles for Ra = 104 and Ra = 106. Pr = 7.02 and ϕ = 0.05

Mentions: An interesting parameter is the distribution of nanoparticles within the cell at steady state. While the particles are initially evenly distributed within the cell, as a result of the existing forces and the fluid flow, particles may be redistributed, settled, or entrapped in the circulations. Figure 5 shows the distribution of the nanoparticle volume fraction at various inclination angles for particle volume fraction of 5 %. Overall, particles remain suspended with minimal accumulation. At Ra = 104, particles are more uniformly distributed than for the case with Ra = 106. Studies on micrometer-sized particle-laden flow usually show particle separation from the base fluid, e.g., [36].Fig. 5


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)

Nanoparticle volume fraction distribution at steady state for various inclination angles for Ra = 104 and Ra = 106. Pr = 7.02 and ϕ = 0.05
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig5: Nanoparticle volume fraction distribution at steady state for various inclination angles for Ra = 104 and Ra = 106. Pr = 7.02 and ϕ = 0.05
Mentions: An interesting parameter is the distribution of nanoparticles within the cell at steady state. While the particles are initially evenly distributed within the cell, as a result of the existing forces and the fluid flow, particles may be redistributed, settled, or entrapped in the circulations. Figure 5 shows the distribution of the nanoparticle volume fraction at various inclination angles for particle volume fraction of 5 %. Overall, particles remain suspended with minimal accumulation. At Ra = 104, particles are more uniformly distributed than for the case with Ra = 106. Studies on micrometer-sized particle-laden flow usually show particle separation from the base fluid, e.g., [36].Fig. 5

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