Limits...
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 versus the inclination angle for various particle loadings for a Ra = 104 and b Ra = 106. Pr = 7.02
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4508308&req=5

Fig7: Variation of the average Nu number along the hot wall versus the inclination angle for various particle loadings for a Ra = 104 and b Ra = 106. Pr = 7.02

Mentions: Figures 7 and 8 investigate the effect of the inclination angle on the average Nu number, and normalized convection heat transfer coefficient with respect to the base fluid. The Nu number and convection heat transfer coefficients are averaged along the hot wall of the enclosure. The first observation is that these two nanofluid heat transfer parameters have a different behavior with respect to the inclination angle. The Nu number significantly changes with the inclination angle and particle loading, where it attains a maximum value at an inclination angle which is a function of the Ra number, and a local minimum value that corresponds to the bottom heating case, albeit within the range of the angles studied here. This has been observed by others, e.g., [10, 12], while the results of ref. [9] do not comply with these findings. We believe that the results presented here are more accurate owing to the two-phase flow LBM approach and proper modeling of the thermophoresis force. At Ra = 104, the maximum Nu number occurs at about 40° (estimated as 45° in refs. [10, 12]), and at Ra = 106, Nu number attains its maximum value at 26° (estimated as 30° in refs. [10, 12]). The contribution of thermophoresis force is also shown in Figs. 7 and 8.Fig. 7


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 versus the inclination angle for various particle loadings for a Ra = 104 and b Ra = 106. Pr = 7.02
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig7: Variation of the average Nu number along the hot wall versus the inclination angle for various particle loadings for a Ra = 104 and b Ra = 106. Pr = 7.02
Mentions: Figures 7 and 8 investigate the effect of the inclination angle on the average Nu number, and normalized convection heat transfer coefficient with respect to the base fluid. The Nu number and convection heat transfer coefficients are averaged along the hot wall of the enclosure. The first observation is that these two nanofluid heat transfer parameters have a different behavior with respect to the inclination angle. The Nu number significantly changes with the inclination angle and particle loading, where it attains a maximum value at an inclination angle which is a function of the Ra number, and a local minimum value that corresponds to the bottom heating case, albeit within the range of the angles studied here. This has been observed by others, e.g., [10, 12], while the results of ref. [9] do not comply with these findings. We believe that the results presented here are more accurate owing to the two-phase flow LBM approach and proper modeling of the thermophoresis force. At Ra = 104, the maximum Nu number occurs at about 40° (estimated as 45° in refs. [10, 12]), and at Ra = 106, Nu number attains its maximum value at 26° (estimated as 30° in refs. [10, 12]). The contribution of thermophoresis force is also shown in Figs. 7 and 8.Fig. 7

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