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Chungpyo Hong - One of the best experts on this subject based on the ideXlab platform.
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on Temperature jump condition for turbulent slip flow in a quasi fully developed region of micro channel with Constant Wall Temperature
International Journal of Thermal Sciences, 2019Co-Authors: Yutaka Asako, Shye Yunn Heng, Chungpyo HongAbstract:Abstract Temperature variation of turbulent slip flows in the quasi-fully developed region of a micro-tube were obtained numerically by solving the energy equation including the substantial derivative of pressure and viscous dissipation terms for the case of Constant Wall Temperature. The fluid was assumed to be an ideal gas with Constant density over the cross-section. The turbulent velocity profile was approximated by the three-layer model of Von Karman. Although the shear work term is not included in the conventional Temperature jump boundary condition explicitly, it is verified that the conventional Temperature jump boundary condition is valid for a slip flow in a micro-tube with Constant Wall Temperature when both viscous dissipation and substantial derivative of pressure terms are included in the energy equation. The total Temperature in the quasi-fully developed region was lower than the Wall Temperature in the case of Kn ≥ 0.01.
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On Temperature Jump Condition for Slip Flow in a Microchannel With Constant Wall Temperature
Journal of Heat Transfer, 2017Co-Authors: Yutaka Asako, Chungpyo HongAbstract:The analytical solution in the fully developed region of a slip flow in a circular microtube with Constant Wall Temperature is obtained to verify the conventional Temperature jump boundary condition when both viscous dissipation (VD) and substantial derivative of pressure (SDP) terms are included in the energy equation. Although the shear work term is not included in the conventional Temperature jump boundary condition explicitly, it is verified that the conventional Temperature jump boundary condition is valid for a slip flow in a microchannel with Constant Wall Temperature when both viscous dissipation and substantial derivative of pressure terms are included in the energy equation. Numerical results are also obtained for a slip flow in a developing region of a circular tube. The results showed that the maximum heat transfer rate decreases with increasing Mach number.
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Convection Heat Transfer in Concentric Micro Annular Tubes With Constant Wall Temperature
ASMEDC, 2009Co-Authors: Chungpyo Hong, Yutaka Asako, Koichi SuzukiAbstract:Heat transfer characteristics of gaseous flows in concentric micro annular tubes with Constant Wall Temperature whose Temperature is lower or higher than the inlet Temperature were numerically investigated. The slip velocity, Temperature jump and shear stress work were considered on the slip boundary. The numerical methodology was based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The computations were performed for two thermal cases. This is, the Wall Temperature was Constant at the outer Wall and inner Wall was adiabatic (Case i) and the Wall Temperature was Constant at the inner Wall and the outer Wall was adiabatic (Case ii). The stagnation Temperature was fixed at 300 K and the computations were done for the Wall Temperature which ranges from 250 K to 350 K. The outer tube radius ranged from 20 to 150 μm with the radius ratio 0.02, 0.05, 0.1, 0.25 and 0.5 and the ratio of length to hydraulic diameter was 100. The stagnation pressure was chosen in such a way that the exit Mach number ranged from 0.1 to 0.8. The outlet pressure was fixed at the atmospheric pressure. The heat transfer characteristics in concentric micro annular tubes were obtained. The bulk Temperature and the total Temperature are compared with those of both cooled and heated cases and also compared with those of the simultaneously developing incompressible flow obtained by SIMPLE algorithm. The results show that the compressible slip flow static bulk Temperature along the length is different from that of incompressible flow. Therefore heat transfer characteristics of the gaseous flow are different from those of the liquid flow and also have different trends whether the Wall Temperature is lower or higher than the inlet Temperature. A correlation for the prediction of the heat transfer rate of gas slip flow in concentric micro annular tubes is proposed.
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convection heat transfer in concentric micro annular tubes with Constant Wall Temperature
Volume 2: Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Computational Heat Transfer, 2009Co-Authors: Chungpyo Hong, Yutaka Asako, Koichi SuzukiAbstract:Heat transfer characteristics of gaseous flows in concentric micro annular tubes with Constant Wall Temperature whose Temperature is lower or higher than the inlet Temperature were numerically investigated. The slip velocity, Temperature jump and shear stress work were considered on the slip boundary. The numerical methodology was based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The computations were performed for two thermal cases. This is, the Wall Temperature was Constant at the outer Wall and inner Wall was adiabatic (Case i) and the Wall Temperature was Constant at the inner Wall and the outer Wall was adiabatic (Case ii). The stagnation Temperature was fixed at 300 K and the computations were done for the Wall Temperature which ranges from 250 K to 350 K. The outer tube radius ranged from 20 to 150 μm with the radius ratio 0.02, 0.05, 0.1, 0.25 and 0.5 and the ratio of length to hydraulic diameter was 100. The stagnation pressure was chosen in such a way that the exit Mach number ranged from 0.1 to 0.8. The outlet pressure was fixed at the atmospheric pressure. The heat transfer characteristics in concentric micro annular tubes were obtained. The bulk Temperature and the total Temperature are compared with those of both cooled and heated cases and also compared with those of the simultaneously developing incompressible flow obtained by SIMPLE algorithm. The results show that the compressible slip flow static bulk Temperature along the length is different from that of incompressible flow. Therefore heat transfer characteristics of the gaseous flow are different from those of the liquid flow and also have different trends whether the Wall Temperature is lower or higher than the inlet Temperature. A correlation for the prediction of the heat transfer rate of gas slip flow in concentric micro annular tubes is proposed.Copyright © 2009 by ASME
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Heat Transfer Characteristics of Gaseous Flows in a Microchannel and a Microtube with Constant Wall Temperature
Numerical Heat Transfer Part A: Applications, 2007Co-Authors: Chungpyo Hong, Yutaka AsakoAbstract:Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in a microchannel and in a microtube with Constant Wall Temperature, whose Temperature is lower than the inlet Temperature (cooled case). The numerical methodology is based on the arbitrary Lagrangian-Eulerian (ALE) method. The stagnation Temperature is fixed at 300 K and the computations were done for the Wall Temperature, which ranges from 250 to 290 K. The bulk Temperature based on the static Temperature and the total Temperature of the cooled case are compared with those of the heated case and also compared with Temperatures of the incompressible flow in a conventional-sized channel. Identical heat transfer coefficients are obtained for both cooled and heated cases of incompressible flow. However, in the case of gaseous flow, different heat transfer coefficients are obtained for each cooled and heated case. A correlation for the prediction of the heat transfer rate of the ...
Yutaka Asako - One of the best experts on this subject based on the ideXlab platform.
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on Temperature jump condition for turbulent slip flow in a quasi fully developed region of micro channel with Constant Wall Temperature
International Journal of Thermal Sciences, 2019Co-Authors: Yutaka Asako, Shye Yunn Heng, Chungpyo HongAbstract:Abstract Temperature variation of turbulent slip flows in the quasi-fully developed region of a micro-tube were obtained numerically by solving the energy equation including the substantial derivative of pressure and viscous dissipation terms for the case of Constant Wall Temperature. The fluid was assumed to be an ideal gas with Constant density over the cross-section. The turbulent velocity profile was approximated by the three-layer model of Von Karman. Although the shear work term is not included in the conventional Temperature jump boundary condition explicitly, it is verified that the conventional Temperature jump boundary condition is valid for a slip flow in a micro-tube with Constant Wall Temperature when both viscous dissipation and substantial derivative of pressure terms are included in the energy equation. The total Temperature in the quasi-fully developed region was lower than the Wall Temperature in the case of Kn ≥ 0.01.
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On Temperature Jump Condition for Slip Flow in a Microchannel With Constant Wall Temperature
Journal of Heat Transfer, 2017Co-Authors: Yutaka Asako, Chungpyo HongAbstract:The analytical solution in the fully developed region of a slip flow in a circular microtube with Constant Wall Temperature is obtained to verify the conventional Temperature jump boundary condition when both viscous dissipation (VD) and substantial derivative of pressure (SDP) terms are included in the energy equation. Although the shear work term is not included in the conventional Temperature jump boundary condition explicitly, it is verified that the conventional Temperature jump boundary condition is valid for a slip flow in a microchannel with Constant Wall Temperature when both viscous dissipation and substantial derivative of pressure terms are included in the energy equation. Numerical results are also obtained for a slip flow in a developing region of a circular tube. The results showed that the maximum heat transfer rate decreases with increasing Mach number.
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Convection Heat Transfer in Concentric Micro Annular Tubes With Constant Wall Temperature
ASMEDC, 2009Co-Authors: Chungpyo Hong, Yutaka Asako, Koichi SuzukiAbstract:Heat transfer characteristics of gaseous flows in concentric micro annular tubes with Constant Wall Temperature whose Temperature is lower or higher than the inlet Temperature were numerically investigated. The slip velocity, Temperature jump and shear stress work were considered on the slip boundary. The numerical methodology was based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The computations were performed for two thermal cases. This is, the Wall Temperature was Constant at the outer Wall and inner Wall was adiabatic (Case i) and the Wall Temperature was Constant at the inner Wall and the outer Wall was adiabatic (Case ii). The stagnation Temperature was fixed at 300 K and the computations were done for the Wall Temperature which ranges from 250 K to 350 K. The outer tube radius ranged from 20 to 150 μm with the radius ratio 0.02, 0.05, 0.1, 0.25 and 0.5 and the ratio of length to hydraulic diameter was 100. The stagnation pressure was chosen in such a way that the exit Mach number ranged from 0.1 to 0.8. The outlet pressure was fixed at the atmospheric pressure. The heat transfer characteristics in concentric micro annular tubes were obtained. The bulk Temperature and the total Temperature are compared with those of both cooled and heated cases and also compared with those of the simultaneously developing incompressible flow obtained by SIMPLE algorithm. The results show that the compressible slip flow static bulk Temperature along the length is different from that of incompressible flow. Therefore heat transfer characteristics of the gaseous flow are different from those of the liquid flow and also have different trends whether the Wall Temperature is lower or higher than the inlet Temperature. A correlation for the prediction of the heat transfer rate of gas slip flow in concentric micro annular tubes is proposed.
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convection heat transfer in concentric micro annular tubes with Constant Wall Temperature
Volume 2: Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Computational Heat Transfer, 2009Co-Authors: Chungpyo Hong, Yutaka Asako, Koichi SuzukiAbstract:Heat transfer characteristics of gaseous flows in concentric micro annular tubes with Constant Wall Temperature whose Temperature is lower or higher than the inlet Temperature were numerically investigated. The slip velocity, Temperature jump and shear stress work were considered on the slip boundary. The numerical methodology was based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The computations were performed for two thermal cases. This is, the Wall Temperature was Constant at the outer Wall and inner Wall was adiabatic (Case i) and the Wall Temperature was Constant at the inner Wall and the outer Wall was adiabatic (Case ii). The stagnation Temperature was fixed at 300 K and the computations were done for the Wall Temperature which ranges from 250 K to 350 K. The outer tube radius ranged from 20 to 150 μm with the radius ratio 0.02, 0.05, 0.1, 0.25 and 0.5 and the ratio of length to hydraulic diameter was 100. The stagnation pressure was chosen in such a way that the exit Mach number ranged from 0.1 to 0.8. The outlet pressure was fixed at the atmospheric pressure. The heat transfer characteristics in concentric micro annular tubes were obtained. The bulk Temperature and the total Temperature are compared with those of both cooled and heated cases and also compared with those of the simultaneously developing incompressible flow obtained by SIMPLE algorithm. The results show that the compressible slip flow static bulk Temperature along the length is different from that of incompressible flow. Therefore heat transfer characteristics of the gaseous flow are different from those of the liquid flow and also have different trends whether the Wall Temperature is lower or higher than the inlet Temperature. A correlation for the prediction of the heat transfer rate of gas slip flow in concentric micro annular tubes is proposed.Copyright © 2009 by ASME
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Heat Transfer Characteristics of Gaseous Flows in a Microchannel and a Microtube with Constant Wall Temperature
Numerical Heat Transfer Part A: Applications, 2007Co-Authors: Chungpyo Hong, Yutaka AsakoAbstract:Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in a microchannel and in a microtube with Constant Wall Temperature, whose Temperature is lower than the inlet Temperature (cooled case). The numerical methodology is based on the arbitrary Lagrangian-Eulerian (ALE) method. The stagnation Temperature is fixed at 300 K and the computations were done for the Wall Temperature, which ranges from 250 to 290 K. The bulk Temperature based on the static Temperature and the total Temperature of the cooled case are compared with those of the heated case and also compared with Temperatures of the incompressible flow in a conventional-sized channel. Identical heat transfer coefficients are obtained for both cooled and heated cases of incompressible flow. However, in the case of gaseous flow, different heat transfer coefficients are obtained for each cooled and heated case. A correlation for the prediction of the heat transfer rate of the ...
Ioan Pop - One of the best experts on this subject based on the ideXlab platform.
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entropy generation between two vertical cylinders in the presence of mhd flow subjected to Constant Wall Temperature
International Communications in Heat and Mass Transfer, 2013Co-Authors: Omid Mahian, Ioan Pop, Hakan F Oztop, Shohel Mahmud, Somchai WongwisesAbstract:Abstract An analytical solution is presented on the entropy generation due to mixed convection between two isothermal cylinders where a transverse magnetic field is applied to the system. The governing equations in cylindrical coordinates are simplified and solved to obtain the distribution of entropy generation and the effects of MHD flow on it. The results for the entropy generation number ( N S ), the Bejan number (Be) and average entropy generation number ( N S,ave ) are presented for different values of the Hartmann numbers, radius ratios and a flow parameter, Gr/Re. The results show that the entropy generation decreases with increases in the magnetic field. In addition, it is found that with decreases in the radius ratio, the effects of MHD flow on the entropy generation are reduced.
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mhd mixed convection boundary layer flow towards a stretching vertical surface with Constant Wall Temperature
International Journal of Heat and Mass Transfer, 2010Co-Authors: Anuar Mohd Ishak, Roslinda Mohd Nazar, Ioan PopAbstract:Abstract This work considers a steady two-dimensional magnetohydrodynamic (MHD) flow of a viscous, incompressible and electrically conducting fluid over a stretching vertical surface with Constant Wall Temperature. The external flow and the stretching velocities are assumed to vary with x , where x is the distance from the slot where the surface is issued. The transformed boundary layer equations are solved numerically for some values of the related parameters, namely the magnetic parameter M , the velocity ratio parameter e and the mixed convection or buoyancy parameter λ , while the Prandtl number Pr is fixed to unity, using a finite-difference scheme known as the Keller-box method. Both assisting and opposing flow cases are considered. It is found that the magnetic parameter M significantly affects the flow and the thermal fields, besides increasing the range of λ for which the solution exists. Dual solutions are found to exist for some range of the mixed convection parameter.
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mixed convection along a vertical cone for fluids of any prandtl number case of Constant Wall Temperature
International Journal of Numerical Methods for Heat & Fluid Flow, 2003Co-Authors: Ioan Pop, T Grosan, M KumariAbstract:An analysis of steady laminar mixed convection boundary layer flow along a vertical cone of Constant Wall Temperature is presented. A mixed convection parameter ξ, as proposed by Lin and Chen, is used to serve as a controlling parameter that determines the relative importance of the forced and the free convection flows. New coordinates and dependent variables are then defined in terms of ξ, so that the transformed non‐similar boundary layer equations give computationally efficient numerical solutions which are valid over the entire range of mixed convection flow from the forced convection limit to the free convection limit for fluids of any Prandtl number. The effects of the mixed convection parameter ξ and the Prandtl number Pr on the velocity and Temperature profiles as well as on the skin friction and heat transfer coefficients are shown for both cases of buoyancy assisting and buoyancy opposing flow conditions.
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mixed convection boundary layer flow from a horizontal circular cylinder in micropolar fluids case of Constant Wall Temperature
International Journal of Numerical Methods for Heat & Fluid Flow, 2003Co-Authors: Roslinda Mohd Nazar, Norsarahaida Amin, Ioan PopAbstract:The laminar mixed convection boundary‐layer flow of a micropolar fluid past a horizontal circular cylinder in a stream flowing vertically upwards has been studied in both cases of a heated and cooled cylinder. The solutions for the flow and heat transfer characteristics are evaluated numerically for different parameters, such as the mixed convection parameter λ, the material parameter K (vortex viscosity parameter) and the Prandtl number Pr=1 and 6.8, respectively. It is found, as for the case of a Newtonian fluid considered for Pr=1, that heating the cylinder delays separation and can, if the cylinder is warm enough, suppress it completely. Cooling the cylinder, on the other side, brings the separation point nearer to the lower stagnation point and for sufficiently cold cylinder there will not be a boundary‐layer on the cylinder. This model problem may solve industrial problems with processing of polymeric liquids, lubricants and molten plastics.
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unsteady heat transfer in impulsive falkner skan flows Constant Wall Temperature case
European Journal of Mechanics B-fluids, 2002Co-Authors: S D Harris, D B Ingham, Ioan PopAbstract:Abstract A theoretical study of the velocity and thermal boundary-layer growth resulting from an impulsively started Falkner–Skan flow is presented in this paper. The forced convection, thermal boundary-layer is produced by the sudden increase of the surface Temperature as it is set into motion. Analytical solutions for the simultaneous development of the thermal and momentum boundary layers are obtained for both small (initial, unsteady flow) and large (steady-state flow) times. These solutions are then matched numerically using a very efficient finite-difference scheme. Some considerable attention to the steady-state flow solution (large time) is also given in this paper. Results of the calculations are presented for a range of values of the Falkner–Skan exponent m and the Prandtl number Pr.
Ching-yang Cheng - One of the best experts on this subject based on the ideXlab platform.
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Soret and Dufour Effects on Mixed Convection Heat and Mass Transfer from a Vertical Wedge in a Porous Medium with Constant Wall Temperature and Concentration
Transport in Porous Media, 2012Co-Authors: Ching-yang ChengAbstract:This work studies the Soret and Dufour effects on the boundary layer flow due to mixed convection heat and mass transfer over a downward-pointing vertical wedge in a porous medium saturated with Newtonian fluids with Constant Wall Temperature and concentration. A suitable coordinate transformation is performed, and the obtained nonsimilar equations are solved by cubic spline collocation method. The effects of the Dufour parameter, Soret parameter, wedge angle parameter, mixed convection variable, and buoyancy ratio on the heat and mass transfer characteristics has been studied. The local Nusselt number is found to decrease when the Dufour parameter is increased. Moreover, an increase in the Soret number leads to a decrease in the local Sherwood number. For natural-convection-dominated regime, an increase in the Soret number leads to an increase in the local Nusselt number for buoyancy assisting flows and a decrease for buoyancy opposing flows. As the wedge angle parameter is increased, the local Nusselt number and the local Sherwood number increases for forced convection and forced-convection-dominated mixed convection. The wedge angle parameter is insignificant for natural convection or natural-convection-dominated mixed convection.
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natural convection heat and mass transfer from a sphere in micropolar fluids with Constant Wall Temperature and concentration
International Communications in Heat and Mass Transfer, 2008Co-Authors: Ching-yang ChengAbstract:This work examines the natural convection heat and mass transfer near a sphere with Constant Wall Temperature and concentration in a micropolar fluid. A coordinate transformation is used to transform the governing equations into nondimensional nonsimilar boundary layer equations and the obtained boundary layer equations are then solved by the cubic spline collocation method. Results for the local Nusselt number and the local Sherwood number are presented as functions of the vortex viscosity parameter, Schmidt number, buoyancy ratio, and Prandtl number. For micropolar fluids, higher viscosity tends to retard the flow and thus decreases the natural convection heat and mass transfer rates from the sphere with Constant Wall Temperature and concentration. Moreover, the natural convection heat and mass transfer rates from a sphere in Newtonian fluids are higher than those in micropolar fluids.
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natural convection heat and mass transfer from a horizontal cylinder of elliptic cross section with Constant Wall Temperature and concentration in saturated porous media
Journal of Mechanics, 2006Co-Authors: Ching-yang ChengAbstract:This work studies the natural convection heat and mass transfer near a horizontal cylinder of elliptic cross section with Constant Wall Temperature and concentration in a fluid-saturated porous medium. A coordinate transformation is used to obtain the nonsimilar governing boundary layer equations. The transformed governing equations are then solved by the cubic spline collocation method. Results for the local Nusselt and Sherwood numbers are presented as functions of the Lewis number, the buoyancy ratio, and the aspect ratio when the major axis of the elliptical cylinder is vertical (slender orientation) and horizontal (blunt orientation). The heat and mass transfer rates of the elliptical cylinder with slender orientation are higher than those with blunt orientation.
Mahdi Zamani - One of the best experts on this subject based on the ideXlab platform.
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nanofluid flow in micro annular tubes at Constant Wall Temperature considering the non uniform distribution of nanoparticles
European Journal of Mechanics B-fluids, 2017Co-Authors: Mahdi Zamani, A Malvandi, S A Moshizi, S J HosseiniAbstract:Abstract In this paper, the modified two-component non-homogeneous mixture model of Buongiorno is developed for the case of forced convection of alumina–water non-homogeneous nanofluid flow in concentric micro-annular tubes at Constant Wall Temperature (CWT). Two different thermal boundary conditions have been considered such that for Case A the inner Wall is adiabatic and the outer Wall is kept at a Constant Temperature while for Case B the inner Wall Temperature remains Constant and the outer Wall is thermally isolated. Assuming a hydrodynamically and thermally fully developed flow, the governing equations of nanofluids in a concentric annulus are reduced to a nonlinear system of ordinary differential equations and solved using an appropriate reciprocal numerical algorithm via Runge–Kutta–Fehlberg method. The effects of N B T (from 0.7 to 10), ϕ B (from 0.01 to 0.03), λ (from 0.05 to 0.2) and ζ (0.4, 0.5 and 0.6) on the non-dimensional volume fraction of nanoparticles, velocity, and Temperature profiles have been investigated for both cases. It is indicated that the anomalous heat transfer enhancement depends on the thermal boundary condition as well as the ratio of thermophoresis and Brownian motion. Furthermore, for Case B, there is an optimum nanoparticle diameter around 0.5 N B T 1 that the thermal performance reaches its peak. However, for Case A, the thermal performance increases as the nanoparticle diameter increases. For both cases, the thermal performance decreases with an increase in the nanoparticle concentration.
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figure of merit for optimization of nanofluid flow in circular microchannel by adapting nanoparticle migration
Applied Thermal Engineering, 2017Co-Authors: A Malvandi, Mahdi Zamani, S J Hosseini, S A MoshiziAbstract:Abstract In this paper, the laminar fully developed flow of alumina/water nanofluid inside circular microchannels subjected to a Constant Wall Temperature (CWT) is theoretically investigated. The effect of nanoparticles migration originating from thermophoretic diffusion (Temperature-gradient driven force) and Brownian diffusion (concentration-gradient driven force) on the thermophysical characteristics of nanofluids has been considered. A Navier's slip condition is considered at the Wall to model the non-equilibrium region at the fluid-solid interface. In order to assume a hydrodynamically and thermally fully developed flow, the governing equations are reduced to a system of ordinary differential equation and solved using the appropriate reciprocal algorithm. The effects of pertinent parameters including the ratio of Brownian motion to thermophoresis ( N BT ), slip parameter ( λ ) and bulk mean nanoparticle volume fraction ( ϕ B ) on the flow and thermal fields are investigated. In addition, the results are compared with the case of Constant heat flux (CHF) at the Wall. The figure of merit ( FoM ) is used to measure the thermal performance of equipment and finding the optimum thermal condition. It is shown that the anomalous heat transfer enhancement depends on the thermal boundary condition as well as the nanoparticles diameter. Furthermore, the optimum value of N BT for the case of Constant Wall Temperature (approximately 1) is found to be greater than that of the Constant Wall heat flux (approximately 0.5). Thus, it can be concluded that the optimum diameter of nanoparticles for the case of Constant Wall Temperature should be smaller than that of Constant Wall heat flux.
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mixed convection of magnetohydrodynamic nanofluids inside microtubes at Constant Wall Temperature
Journal of Magnetism and Magnetic Materials, 2017Co-Authors: S A Moshizi, S J Hosseini, Mahdi Zamani, A MalvandiAbstract:Abstract Laminar fully developed mixed convection of magnetohydrodynamic nanofluids inside microtubes at a Constant Wall Temperature (CWT) under the effects of a variable directional magnetic field is investigated numerically. Nanoparticles are assumed to have slip velocities relative to the base fluid owing to thermophoretic diffusion (Temperature gradient driven force) and Brownian diffusion (concentration gradient driven force). The no-slip boundary condition is avoided at the fluid-solid mixture to assess the non-equilibrium region at the fluid-solid interface. A scale analysis is performed to estimate the relative significance of the pertaining parameters that should be included in the governing equations. After the effects of pertinent parameters on the pressure loss and heat transfer enhancement were considered, the figure of merit (FoM) is employed to evaluate and optimize the thermal performance of heat exchange equipment. The results indicate the optimum thermal performance is obtained when the thermophoresis overwhelms the Brownian diffusion, which is for larger nanoparticles. This enhancement boosts when the buoyancy force increases. In addition, increasing the magnetic field strength and slippage at the fluid-solid interface enhances the thermal performance.
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fully developed mixed convection of nanofluids in microtubes at Constant Wall Temperature anomalous heat transfer rate and thermal performance
Advanced Powder Technology, 2017Co-Authors: S J Hosseini, A Malvandi, S A Moshizi, Mahdi ZamaniAbstract:Abstract This is a theoretical investigation on fully developed mixed convective flow of nanofluids inside microtubes subjected to a Constant Wall Temperature (CWT). The modified Buongiorno model is used for the nanofluids which fully accounts for the distribution of nanoparticles concentration on thermophysical properties. The effect of nanoparticles migration originating from the nano-scale diffusivities including thermophoretic diffusion (Temperature-gradient driven force) and Brownian diffusion (concentration-gradient driven force) on the thermophysical characteristics of nanofluids has been considered. A Navier's slip condition is considered at the Wall to model the non-equilibrium region at the fluid-solid interface in micro-scale channels. A scale analysis is performed to estimate the relative significance of the pertaining parameters that should be included in the governing equations. The effects of pertinent parameters including the ratio of Brownian motion to thermophoresis (NBT), slip parameter (λ), mixed convective parameter (Nr), and bulk mean nanoparticle volume fraction (ϕB) on the flow and thermal fields are investigated. The figure of merit (FoM) is used to measure the thermal performance of equipment and finding the optimum thermal condition. It is shown that increasing the buoyancy force would enhance the heat transfer rate, especially for the larger nanoparticles. Also, larger nanoparticles enhance the thermal performance based on a required heat transfer rate with the lowest penalty in the pressure drop.