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Morteza Eslamian - One of the best experts on this subject based on the ideXlab platform.
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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
Nanoscale Research Letters, 2015Co-Authors: Mahmoud Ahmed, Morteza EslamianAbstract: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.
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effect of Thermophoresis on natural convection in a rayleigh benard cell filled with a nanofluid
International Journal of Heat and Mass Transfer, 2015Co-Authors: Morteza Eslamian, Mahmoud Ahmed, M F Eldosoky, M.z. SaghirAbstract:Abstract The objective of this paper is to clarify the role of Thermophoresis in laminar natural convection in a Rayleigh–Benard cell filled with a water-based nanofluid and to study its relative importance compared to other effects, in an attempt to correct the present confusing interpretation of the magnitude of the Thermophoresis coefficient in nanofluids. The major forces are introduced and the transport equations are solved using a two-phase lattice Boltzmann method (LBM) for a laminar flow with Ra numbers up to 106 with various particle loadings (particle volume fractions). The results indicate an increase in the average Nu number with an increase in the Ra number and particle loading. An increase in the Nu number for a 10% particle loading at Ra = 106 is less than 20%. When Thermophoresis effect is taken into consideration, an increase in the Nu number is predicted, which is about 10%. Therefore, it is concluded that using a nanofluid in bottom-heated laminar natural convection results in a considerable increase in heat transfer rate and Thermophoresis force is a significant contributor to heat transfer augmentation, particularly for high Ra numbers (Ra ∼ 106 and higher). It is observed that at low Ra numbers (weak convective flows), the nanofluid behaves homogenously, but at higher Ra numbers, it starts to behave heterogeneously.
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Effect of Thermophoresis on natural convection in a Rayleigh–Benard cell filled with a nanofluid
International Journal of Heat and Mass Transfer, 2015Co-Authors: Morteza Eslamian, Mahmoud Ahmed, M.f. El-dosoky, M.z. SaghirAbstract:Abstract The objective of this paper is to clarify the role of Thermophoresis in laminar natural convection in a Rayleigh–Benard cell filled with a water-based nanofluid and to study its relative importance compared to other effects, in an attempt to correct the present confusing interpretation of the magnitude of the Thermophoresis coefficient in nanofluids. The major forces are introduced and the transport equations are solved using a two-phase lattice Boltzmann method (LBM) for a laminar flow with Ra numbers up to 106 with various particle loadings (particle volume fractions). The results indicate an increase in the average Nu number with an increase in the Ra number and particle loading. An increase in the Nu number for a 10% particle loading at Ra = 106 is less than 20%. When Thermophoresis effect is taken into consideration, an increase in the Nu number is predicted, which is about 10%. Therefore, it is concluded that using a nanofluid in bottom-heated laminar natural convection results in a considerable increase in heat transfer rate and Thermophoresis force is a significant contributor to heat transfer augmentation, particularly for high Ra numbers (Ra ∼ 106 and higher). It is observed that at low Ra numbers (weak convective flows), the nanofluid behaves homogenously, but at higher Ra numbers, it starts to behave heterogeneously.
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natural convection in a differentially heated square enclosure filled with a nanofluid significance of the Thermophoresis force and slip drift velocity
International Communications in Heat and Mass Transfer, 2014Co-Authors: Mahmoud Ahmed, Morteza EslamianAbstract:Abstract Natural convection in a differentially-heated enclosure is studied, with emphasis on the role of Thermophoresis force and slip/drift velocity on particle surface with respect to the main flow. In nanofluid literature, Thermophoresis force has been either neglected or erroneous expressions have been used to model its effect. Here, a sufficiently accurate expression for Thermophoresis coefficient in liquid solutions and mixtures, backed with a theoretical foundation is introduced and used. A two-phase lattice Boltzmann method (LBM) is employed to capture the slip velocity created by Brownian, Thermophoresis and gravitational forces. At Ra = 10 6 and particle volume concentration of 5%, the nanofluid Nu number is 13% higher than that of the pure fluid, where 5% out of 13% of the enhancement is due to the Thermophoresis effect.
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Natural convection in a differentially-heated square enclosure filled with a nanofluid: Significance of the Thermophoresis force and slip/drift velocity
International Communications in Heat and Mass Transfer, 2014Co-Authors: Mahmoud Ahmed, Morteza EslamianAbstract:Abstract Natural convection in a differentially-heated enclosure is studied, with emphasis on the role of Thermophoresis force and slip/drift velocity on particle surface with respect to the main flow. In nanofluid literature, Thermophoresis force has been either neglected or erroneous expressions have been used to model its effect. Here, a sufficiently accurate expression for Thermophoresis coefficient in liquid solutions and mixtures, backed with a theoretical foundation is introduced and used. A two-phase lattice Boltzmann method (LBM) is employed to capture the slip velocity created by Brownian, Thermophoresis and gravitational forces. At Ra = 10 6 and particle volume concentration of 5%, the nanofluid Nu number is 13% higher than that of the pure fluid, where 5% out of 13% of the enhancement is due to the Thermophoresis effect.
Mahmoud Ahmed - One of the best experts on this subject based on the ideXlab platform.
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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
Nanoscale Research Letters, 2015Co-Authors: Mahmoud Ahmed, Morteza EslamianAbstract: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.
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effect of Thermophoresis on natural convection in a rayleigh benard cell filled with a nanofluid
International Journal of Heat and Mass Transfer, 2015Co-Authors: Morteza Eslamian, Mahmoud Ahmed, M F Eldosoky, M.z. SaghirAbstract:Abstract The objective of this paper is to clarify the role of Thermophoresis in laminar natural convection in a Rayleigh–Benard cell filled with a water-based nanofluid and to study its relative importance compared to other effects, in an attempt to correct the present confusing interpretation of the magnitude of the Thermophoresis coefficient in nanofluids. The major forces are introduced and the transport equations are solved using a two-phase lattice Boltzmann method (LBM) for a laminar flow with Ra numbers up to 106 with various particle loadings (particle volume fractions). The results indicate an increase in the average Nu number with an increase in the Ra number and particle loading. An increase in the Nu number for a 10% particle loading at Ra = 106 is less than 20%. When Thermophoresis effect is taken into consideration, an increase in the Nu number is predicted, which is about 10%. Therefore, it is concluded that using a nanofluid in bottom-heated laminar natural convection results in a considerable increase in heat transfer rate and Thermophoresis force is a significant contributor to heat transfer augmentation, particularly for high Ra numbers (Ra ∼ 106 and higher). It is observed that at low Ra numbers (weak convective flows), the nanofluid behaves homogenously, but at higher Ra numbers, it starts to behave heterogeneously.
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Effect of Thermophoresis on natural convection in a Rayleigh–Benard cell filled with a nanofluid
International Journal of Heat and Mass Transfer, 2015Co-Authors: Morteza Eslamian, Mahmoud Ahmed, M.f. El-dosoky, M.z. SaghirAbstract:Abstract The objective of this paper is to clarify the role of Thermophoresis in laminar natural convection in a Rayleigh–Benard cell filled with a water-based nanofluid and to study its relative importance compared to other effects, in an attempt to correct the present confusing interpretation of the magnitude of the Thermophoresis coefficient in nanofluids. The major forces are introduced and the transport equations are solved using a two-phase lattice Boltzmann method (LBM) for a laminar flow with Ra numbers up to 106 with various particle loadings (particle volume fractions). The results indicate an increase in the average Nu number with an increase in the Ra number and particle loading. An increase in the Nu number for a 10% particle loading at Ra = 106 is less than 20%. When Thermophoresis effect is taken into consideration, an increase in the Nu number is predicted, which is about 10%. Therefore, it is concluded that using a nanofluid in bottom-heated laminar natural convection results in a considerable increase in heat transfer rate and Thermophoresis force is a significant contributor to heat transfer augmentation, particularly for high Ra numbers (Ra ∼ 106 and higher). It is observed that at low Ra numbers (weak convective flows), the nanofluid behaves homogenously, but at higher Ra numbers, it starts to behave heterogeneously.
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natural convection in a differentially heated square enclosure filled with a nanofluid significance of the Thermophoresis force and slip drift velocity
International Communications in Heat and Mass Transfer, 2014Co-Authors: Mahmoud Ahmed, Morteza EslamianAbstract:Abstract Natural convection in a differentially-heated enclosure is studied, with emphasis on the role of Thermophoresis force and slip/drift velocity on particle surface with respect to the main flow. In nanofluid literature, Thermophoresis force has been either neglected or erroneous expressions have been used to model its effect. Here, a sufficiently accurate expression for Thermophoresis coefficient in liquid solutions and mixtures, backed with a theoretical foundation is introduced and used. A two-phase lattice Boltzmann method (LBM) is employed to capture the slip velocity created by Brownian, Thermophoresis and gravitational forces. At Ra = 10 6 and particle volume concentration of 5%, the nanofluid Nu number is 13% higher than that of the pure fluid, where 5% out of 13% of the enhancement is due to the Thermophoresis effect.
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Natural convection in a differentially-heated square enclosure filled with a nanofluid: Significance of the Thermophoresis force and slip/drift velocity
International Communications in Heat and Mass Transfer, 2014Co-Authors: Mahmoud Ahmed, Morteza EslamianAbstract:Abstract Natural convection in a differentially-heated enclosure is studied, with emphasis on the role of Thermophoresis force and slip/drift velocity on particle surface with respect to the main flow. In nanofluid literature, Thermophoresis force has been either neglected or erroneous expressions have been used to model its effect. Here, a sufficiently accurate expression for Thermophoresis coefficient in liquid solutions and mixtures, backed with a theoretical foundation is introduced and used. A two-phase lattice Boltzmann method (LBM) is employed to capture the slip velocity created by Brownian, Thermophoresis and gravitational forces. At Ra = 10 6 and particle volume concentration of 5%, the nanofluid Nu number is 13% higher than that of the pure fluid, where 5% out of 13% of the enhancement is due to the Thermophoresis effect.
D. J. Biswas - One of the best experts on this subject based on the ideXlab platform.
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Exploitation of Thermophoresis effect to prevent re-deposition of expelled particulates in laser assisted surface cleaning
Journal of Applied Physics, 2012Co-Authors: M.b. Sai Prasad, Tatsat Dwivedi, Gautam C. Patil, J. Padma Nilaya, D. J. BiswasAbstract:Evidence in the improvement of the cleaning efficiency in the case of laser assisted surface decontamination wherein the phenomenon of Thermophoresis has been exploited to prevent re-deposition of minute particulates is reported. The Thermophoresis effect was made to set in by providing an appropriate temperature gradient in the vicinity of the laser exposed surface. The effectiveness of Thermophoresis towards improving the laser assisted cleaning efficiency of polished stainless steel (SS) surface contaminated with copper telluride metal chalcogenide nanoparticles has been studied and compared with that obtained under ambient and dynamic vacuum conditions. [ABSTRACT FROM AUTHOR]
Dieter Braun - One of the best experts on this subject based on the ideXlab platform.
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Understanding the similarity in Thermophoresis between single- and double-stranded DNA or RNA.
Physical Review E, 2015Co-Authors: Maren Reichl, Mario Herzog, Ferdinand Greiss, Manuel Wolff, Dieter BraunAbstract:Thermophoresis is the movement of molecules in a temperature gradient. For aqueous solutions its microscopic basis is debated. Understanding Thermophoresis for this case is, however, important since it proved very useful to detect the binding affinity of biomolecules and since Thermophoresis could have played an important role in early molecular evolution. Here we discuss why the Thermophoresis of single- and double-stranded oligonucleotides - DNA and RNA - is surprisingly similar. This finding is understood by comparing the spherical capacitor model for single-stranded species with the case of a rod-shaped model for double-stranded oligonucleotides. The approach describes Thermophoresis of DNA and RNA with fitted effective charges consistent with electrophoresis measurements and explains the similarity between single- and double-stranded species. We could not confirm the sign change for the Thermophoresis of single- versus double-stranded DNA in crowded solutions containing polyethylene glycol [Y. T. Maeda, T. Tlusty, and A. Libchaber, Proc. Natl. Acad. Sci. USA 109, 17972 (2012)], but find a salt-independent offset while the Debye length dependence still satisfies the capacitor model. Overall, the analysis documents the continuous progress in the microscopic understanding of Thermophoresis.
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Thermophoresis of single stranded DNA.
ELECTROPHORESIS, 2010Co-Authors: Philipp Reineck, Christoph J. Wienken, Dieter BraunAbstract:The manipulation and analysis of biomolecules in native bulk solution is highly desired; however, few methods are available. In Thermophoresis, the thermal analog to electrophoresis, molecules are moved along a microscopic temperature gradient. Its theoretical foundation is still under debate, but practical applications for analytics in biology show considerable potential. Here we measured the Thermophoresis of highly diluted single stranded DNA using an all-optical capillary approach. Temperature gradients were created locally by an infrared laser. The thermal depletion of oligonucleotides of between 5 and 50 bases in length were investigated by fluorescence at various salt concentrations. To a good approximation, the previously tested capacitor model describes Thermophoresis: the Soret coefficient linearly depends on the Debye length and is proportional to the DNA length to the power of 0.35, dictated by the conformation-based size scaling of the diffusion coefficient. The results form the basis for quantitative DNA analytics using Thermophoresis.
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Nonlinear Thermophoresis beyond Local Equilibrium Criterion
arXiv: Statistical Mechanics, 2006Co-Authors: Stefan Duhr, Dieter BraunAbstract:Thermophoresis (thermodiffusion, Soret effect) moves molecules along thermal gradients. We measure its phenomenological linear drift relation by single particle tracking in convection-free settings. For moderate thermal gradients, drift velocity depends linearly on the gradient. However, for strong thermal gradients, we find a nonlinear dependence of the drift on the applied gradient for large Soret coefficient and particle radius. Interestingly, the onset of the nonlinearity coincides with a local disequilibrium of the particle. Nonlinear Thermophoresis resolves several fundamental contradictions between thermophoretic experiments and theory.
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Thermophoresis of DNA determined by microfluidic fluorescence
The European Physical Journal E, 2004Co-Authors: S. Duhr, Silvia Arduini, Dieter BraunAbstract:We describe a microfluidic all-optical technique to measure the Thermophoresis of molecules. Within micrometer-thick chambers, we heat aqueous solutions with a micrometer-sized focus of infrared light. The temperature increase of about 1 K is monitored with temperature-sensitive fluorescent dyes. We test the approach in measuring the Thermophoresis of DNA. We image the concentration of DNA in a second fluorescence-color channel. DNA is depleted away from the heated spot. The profile of depletion is fitted by the thermophoretic theory to reveal the Soret coefficient. We evaluate the method with numerical 3D calculations of temperature profiles, drift, convection and thermophoretic depletion using finite element methods. The approach opens new ways to monitor Thermophoresis at the single molecule level, near boundaries and in complex mixtures. The flexible microfluidic setting is a good step towards microfluidic applications of Thermophoresis in biotechnology.
Ching-yang Cheng - One of the best experts on this subject based on the ideXlab platform.
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Free convection of non-Newtonian nanofluids about a vertical truncated cone in a porous medium
International Communications in Heat and Mass Transfer, 2012Co-Authors: Ching-yang ChengAbstract:Abstract This work studies the free convection heat transfer over a truncated cone embedded in a porous medium saturated by a non-Newtonian power-law nanofluid with constant wall temperature and constant wall nanoparticle volume fraction. The effects of Brownian motion and Thermophoresis are incorporated into the model for nanofluids. A coordinate transformation is performed, and the obtained nonsimilar equations are solved by the cubic spline collocation method. The effects of the power-law index, Brownian motion parameter, Thermophoresis parameter and buoyancy ratio on the temperature, nanoparticle volume fraction and velocity profiles are discussed. The reduced Nusselt numbers are plotted as functions of the power-law index, Thermophoresis parameter, Brownian parameter, Lewis number, and buoyancy ratio. Results show that increasing the Thermophoresis parameter or the Brownian parameter tends to decrease the reduced Nusselt number. Moreover, the reduced Nusselt number increases as the power-law index is increased.
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natural convection boundary layer flow over a truncated cone in a porous medium saturated by a nanofluid
International Communications in Heat and Mass Transfer, 2012Co-Authors: Ching-yang ChengAbstract:Abstract This work studies the natural convection boundary layer flow over a truncated cone embedded in a porous medium saturated by a nanofluid with constant wall temperature and constant wall nanoparticle volume fraction. The effects of Brownian motion and Thermophoresis are incorporated into the model for nanofluids. A suitable coordinate transformation is performed, and the obtained nonsimilar equations are solved by the cubic spline collocation method. The effect of the Brownian motion parameter and Thermophoresis parameter on the temperature, nanoparticle volume fraction and velocity profiles are discussed. The effects of the Thermophoresis parameter, Brownian parameter, Lewis number, and buoyancy ratio on the local Nusselt number have been studied. Results show that an increase in the Thermophoresis parameter or the Brownian parameter tends to decrease the local Nusselt number. Moreover, the local Nusselt number increases as the buoyancy ratio or the Lewis number is decreased.
