Entire Mixed Convection Regime Research Articles

Mixed Bioconvective Flow Over a Wedge in Porous Media Drenched with a Nanofluid

A mathematical model is accentuated the mixed bioconvective flow on a vertical wedge in a Darcy porous medium filled with a nanofluid containing both nanoparticles and gyrotactic microorganisms. Thermophoresis and Brownian motion impacts are addressed to consolidate energy and concentration equations with passivelycontrolled boundary conditions. A mixed convective parameter for the whole regime of the mixed convective is appointed. The system of governing partial differential equations is converted into a non-similar set, which are then solved by an implicit finite difference method. By taking the impacts of the varying pertinent parameters, namely, the bioconvection nanofluids and wedge angle parameters in the entire mixed convection regime, the numerical results are analyzed graphically for the dimensionless the velocity, temperature, nanoparticle volume fraction and the density motile microorganisms profiles as well as the local Nusselt and motile microorganism numbers.

Mixed Bioconvective Flow Over a Wedge in Porous Media Drenched with a Nanofluid

A mathematical model is accentuated the mixed bioconvective flow on a vertical wedge in a Darcy porous medium filled with a nanofluid containing both nanoparticles and gyrotactic microorganisms. Thermophoresis and Brownian motion impacts are addressed to consolidate energy and concentration equations with passivelycontrolled boundary conditions. A mixed convective parameter for the whole regime of the mixed convective is appointed. The system of governing partial differential equations is converted into a non-similar set, which are then solved by an implicit finite difference method. By taking the impacts of the varying pertinent parameters, namely, the bioconvection nanofluids and wedge angle parameters in the entire mixed convection regime, the numerical results are analyzed graphically for the dimensionless the velocity, temperature, nanoparticle volume fraction and the density motile microorganisms profiles as well as the local Nusselt and motile microorganism numbers.

Optimal plate spacing for mixed convection from an array of vertical isothermal plates

Numerical simulations of mixed convection of air between vertical isothermal surfaces were conducted in order to determine the optimum spacing corresponding to the peak heat flux transferred from an array of isothermal, parallel plates cooled by mixed convection. Comparisons between approximate analytical solutions for natural and forced convection are first discussed. It is shown that the agreement is fairly good. From the computations carried out for aiding mixed convection by assuming a pressure drop at the outlet section rather than a constant flow rate, it is numerically predicted that the optimum spacing is smaller than those for pure natural or pure forced convection. This spacing is determined according to the pressure drop. As a sample, we considered an array of 10 cm -height, isothermal surfaces at temperature Th = 340 K with air as the working fluid entering into the channels at T0 = 300 K. The increases in heat flux corresponding to the optimal spacing are discussed for outlet pressure drops ranging from −0.1 Pa to −1 Pa. Such a range covers the entire laminar mixed convection regime for this specific application.

Influence of radiation on mixed convection over a wedge in non-Darcy porous medium

The influences of radiation on mixed convection flow of an optically dense viscous fluid along an isothermal wedge embedded in non-Darcy porous medium, in the presence of heat source/sink are numerically investigated. The entire mixed convection regime is covered by a single parameter χ from the pure free convection limit (χ=0) to the pure forced convection limit (χ=1). Forchheimer’s extension is employed to describe the fluid flow in the porous medium and the Rosseland diffusion approximation is considered to describe the radiative heat flux in the energy equation. The governing equations, including internal heat source/sink, are first transformed into a dimensionless form by the nonsimilar transformation and then solved by the Keller box method. The effect of the radiation parameter, mixed convection parameter, Forchheimer number and heat source/sink parameter on the velocity and temperature profiles as well as on the local Nusselt number is presented and analyzed. The results are compared with those known from the literature and excellent agreement between the results is obtained.

HALL CURRENT AND OHMIC HEATING EFFECTS ON MIXED CONVECTION BOUNDARY LAYER FLOW OF A MICROPOLAR FLUID FROM A ROTATING CONE WITH POWER-LAW VARIATION IN SURFACE TEMPERATURE

The problem of laminar mixed convection boundary layer flow of an electrically conducting micropolar fluid from a constantly rotating cone is analyzed, taking into account the effects of Hall current and Ohmic heating. The flow is subjected to a uniform strong transverse magnetic field normal to the cone surface. In this study, the surface temperature is assumed to vary as a power of the axial coordinate measured along the cone surface. A non-similar mixed convection parameter and a pseudo-similarity variable η are introduced to cast the governing boundary layer equations into a system of dimensionless equations, which are solved numerically. The mixed convection parameter is chosen to cover the entire regime of mixed convection from the pure forced limit to the pure free convection limit. Results for the velocity, angular velocity and thermal functions are displayed for a range of values of magnetic parameter, Hall parameter and Eckert number

Non-Darcy mixed convection in power-law fluids along a non-isothermal horizontal surface in a porous medium

The non-similar non-Darcy mixed convection from a horizontal surface in a porous medium saturated with a power-law type non-Newtonian fluid has been studied. Non-similarity solutions have been obtained for the case of a variable surface temperature of the form T w( x)= T ∞± Ax λ , λ≠1/2. It has been found that for λ=1/2, self-similar solution exists. A single mixed convection parameter has been used which covers the entire regime of mixed convection from pure forced convection to pure free convection limits. Both these limiting flows admit self-similar solutions. The partial differential equations governing the non-similar flow and the ordinary differential equations governing the self-similar flow have been solved numerically. The buoyancy force and the wall temperature have significant influence on the heat transfer and the velocity at the wall. For a fixed buoyancy force, the heat transfer and the velocity at the wall decrease with increasing non-Newtonian parameter, non-Darcy parameter and Peclet number.

Variable permeability effects on mixed convection along a vertical wedge embedded in a porous medium with variable surface heat flux

The problem of mixed convection from impermeable vertical wedge in a fluid saturated porous medium incorporating the variation of permeability and thermal conductivity is analyzed. A nonsimilarity solution is obtained for the case of variable surface heat flux in the form q w ( x)= bx m . The entire mixed convection regime is covered by the single nonsimilarity parameter ξ=[1+( Ra x / Pe x 3/2) 1/3] −1 from pure forced convection ( ξ=1) to pure free convection ( ξ=0). A finite-difference scheme was used to solve the system of transformed governing equations. Velocity and temperature profiles, and local Nusselt number are presented. The wedge angle geometry parameter is ranged from 0 to 1.

Local nonsimilarity solutions for mixed convection boundary layer flow of a micropolar fluid on horizontal flat plates with variable surface temperature

An analysis is performed to study the heat transfer characteristics of laminar mixed convection boundary layer flow of a micropolar fluid over a semi-infinite horizontal flat plate with nonuniform surface temperatures. The surface temperature is assumed to vary as a power of the axial coordinate measured from the leading edge of the plate. A nonsimilar mixed convection parameter ξ and a pseudo-similarity variable η are introduced to cast the governing boundary layer equations into a system of dimensionless equations which are solved numerically using finite difference method. The mixed convection parameter is chosen to cover the entire regime of mixed convection from the pure forced convection limit to the pure free convection limit. The effect of material parameter, the exponent for the power-law variation in wall temperature and the nonsimilar mixed convection parameter are considered. The micropolar fluids are observed to display drag reduction and reduce surface heat transfer rate when compared to Newtonian fluid. The effect of the buoyancy force results in the enhancements of friction factor, heat transfer rate and wall couple stress. The local heat transfer rate is found to increase with increase in the exponent value of the power-low variation in wall temperature.

Mixed convection boundary layer flow of a micropolar fluid on a horizontal flat plate with power law variation in surface temperature

An analysis is performed to study the heat transfer characteristics of laminar mixed convection boundary layer flow of a micropolar fluid over a semi-infinite horizontal flat plate with non-uniform surface temperatures. The surface temperature is assumed to vary as a power of the axial coordinate measured from the leading edge of the plate. A nonsimilar mixed convection parameter ξ and a pseudo-similarity variable η are introduced to cast the governing boundary layer equations into a system of dimensionless equations which are solved numerically using finite difference method. The mixed convection parameter is chosen to cover the entire regime of mixed convection from the pure forced convection limit to the pure free convection limit. The effect of material parameter, the exponent for the power-law variation in wall temperature and the nonsimilar mixed convection parameter are considered. The micropolar fluids are observed to display drag reduction and reduce surface heat transfer rate when compared to Newtonian fluid. The effect of the buoyancy force results in the enhancements of friction factor, heat transfer rate and wall couple stress. The local heat transfer rate is found to be increase with increasing in the exponent value of the power-low variation in wall temperature.

Influence of variable permeability on combined convection along a nonisothermal wedge in a saturated porous medium.

Mixed convection along a vertical nonisothermal wedge embedded in a fluid-saturated porous media incorporating the variation of permeability and thermal conductivity is studied. The surface temperature is assumed to vary as a power of the axial coordinate measured from the leading edge of the plate. A nonsimilar mixed convection parameter ζ and a pseudo-similarity variable η are introduced to cast the governing boundary layer equations into a system of dimensionless equations which are solved numerically using finite difference method. The entire mixed convection regime is covered by the single nonsimilarity parameter ζ=[1+(Ra x /Pe x )1/2]−1 from pure forced convection (ζ=1) to pure free convection (ζ=0). The problem is solved using nonsimilarity solution for the case of variable wall temperature. Velocity and temperature profiles as well as local Nusselt number are presented. The wedge angle geometry parameter is ranged from 0 to 1.

FILM CONDENSATION OF SATURATED AND SUPERHEATED VAPORS ALONG ISOTHERMAL VERTICAL SURFACES IN MIXED CONVECTION

An analysis for condensation from an isothermal vertical flat plate in mixed convection is reported. The entire mixed convection regime is divided into two regions. One region covers the forced-convection-dominated regime, and the other covers the free-convection-dominated regime. The governing system of equations is first transformed into a dimensionless form by the nonsimilar transformation, separately for each regime, and then solved using the local nonsimilarity method along with a finite difference scheme. Two nonsimilarity parameters are introduced. The parameter xi f = Grx Re2 x characterizes the effect of buoyancy force on forced convection, while the parameter xi n = Rex Gr1 x /2 characterizes the effect of forced flow on free convection. Numerical results for pure steam and refrigerant R-134a are presented for both saturated and superheated cases. It is found that the buoyancy force significantly increases the wall shear stress and condensate mass flux. To a lesser degree, the buoyancy force also increases the wall heat flux. Superheating is found to have an insignificant effect on wall heat flux for a pure vapor.

Mixed convection heat transfer from a horizontal plate with variable surface heat flux in a porous medium

In this article nonsimilarity solution for mixed convection from a horizontal surface in a saturated porous medium was obtained for the case of variable surface heat flux. The entire mixed convection regime, ranging from pure forced convection to pure free convection, is considered by introducing a single nonsimilarity parameter. Heat transfer results are predicted by employing four different flow models, namely, Darcy's law, the Ergun model, and the Brinkman-Forchheimer-extended Darcy model with constant and variable porosity. The variable porosity effect is approximated by an exponential function. Effects of transverse thermal dispersion are taken into consideration in the energy equation, along with variable stagnant thermal conductivities. The formulation of the present problem shows that the flow and heat transfer characteristics depend on five parameters, that is, the power in the variation of surface heat flux, the nonsimilarity mixed-convection parameter, the inertia effect parameter, the boundary effect parameter, and the ratio of thermal conductivity of the fluid phase to that of the solid phase. Numerical results for the local Nusselt number variations, based on the various flow models, are presented for the entire mixed convection regime. The impacts␣of different governing parameters on the heat transfer results are thoroughly investigated.

Nonsimilar solutions for non-Darcy mixed convection from a nonisothermal horizontal surface in a porous medium

The nonsimilar non-Darcy mixed convection adjacent to a horizontal surface in a saturated porous medium is analyzed. Nonsimilarity solutions are obtained for the case of variable surface temperature in the form T w( x)= T ∞+ ax n . The analysis is performed for the entire mixed convection regime which is divided into two regions. The first region covers the forced-convection-dominated regime and the second region covers the free-convection-dominated regime. The Darcy–Brinkman–Forchheimer equation is used as the momentum equation, and the effect of near-wall porosity variation is approximated by an exponential function. The effects of thermal dispersion and variable stagnant thermal conductivities are taken into consideration in the energy equation. Velocity and temperature profiles and local Nusselt numbers are presented for different governing parameters. Effects of non-Darcy flow phenomena on the heat transfer characteristics are thoroughly examined.

MIXED CONVECTION BOUNDARY LAYER FLOW OF A MICROPOLAR FLUID ON A HORIZONTAL PLATE

An analysis is performed to study the heat transfer characteristics of laminar mixed convection boundary layer flow of a micropolar fluid past a semi-infinite horizontal fiat plate with variable surface heat flux. A nonsimilar mixed convection parameter £ and a pseudosimilarity variable v are introduced to cast the governing boundary layer equations into a system of dimensionless equations, which are solved numerically using the finite difference method. A single mixed convection parameter is used to cover the entire regime of mixed convection from the pure forced convection limit to the pure free convection limit. The effect of material parameters, the power-law variation of surface heat flux, nonsimilar mixed convection parameter and Prandtl number are considered. The micropolar fluids are observed to display drag reduction and reduced surface heat transfer rate when compared to Newtonian fluids. The effect of the buoyancy force results in the enhancements of friction factor, heat transfer rate and wall couple stress.

Nonsimilarity solutions for non-Darcy mixed convection from horizontal surfaces in a porous medium

Non-Darcy mixed convection in a porous medium from horizontal surfaces with variable surface heat flux of the power-law distribution is analyzed. The entire mixed convection regime is divided into two regions. The first region covers the forced convection dominated regime where the dimensionless parameter ζ f =Ra* x /Pe2 x is found to characterize the effect of buoyancy forces on the forced convection with K′U∞/ν characterizing the effect of inertia resistance. The second region covers the natural convection dominated regime where the dimensionless parameter ζ n =Pe x /Ra*1/2 x is found to characterize the effect of the forced flow on the natural convection, with (K′U∞/ν)Ra*1/2 x /Pe x characterizing the effect of inertia resistance. To obtain the solution that covers the entire mixed convection regime the solution of the first regime is carried out for ζ f =0, the pure forced convection limit, to ζ f =1 and the solution of the second is carried out for ζ n =0, the pure natural convection limit, to ζ n =1. The two solutions meet and match at ζ f =ζ n =1, and R* h =G* h .

Non-darcy mixed convection over a vertical flat plate in porous media with variable wall heat flux

The problem of non-Darcy mixed convection along a vertical flat plate embedded in a saturated porous medium is analyzed for the case of variable surface heat flux. Based on three different flow models, the influences of non-Darcy flow phenomena on mixed convection from a vertical surface are thoroughly investigated. The wall effect on porosity variation is approximated by an exponential function. The effects of thermal dispersion and variable stagnant thermal conductivity are taken into consideration in the energy equation. The entire regime of mixed convection, including the two limits of pure forced convection and pure free convection, is covered by employing a single nonsimilarity parameter. The resulting nonsimilar system of equations is solved using a finite difference method. Results are presented for temperature and velocity profiles, and local Nusselt number for representative values of different controlling parameters.

MHD Mixed Convection from a Horizontal Cylinder in a Porous Medium.

Mixed convection from a horizontal cylinder imbedded in saturated electrically conducting fluid is investigated using nonsimilarity boundary layer transformation. Variable wall temperature is assumed at the cylinder surface as the thermal boundary condition. The problem is solved numerically using the finite difference technique and double-checked using a local nonsimilarity solution. The effects of the magnetic field on the velocity and temperature profiles, wall shear stress, and Nusselt number are presented. The non-Darican flow model is adopted. The effects of the inertial and boundary parameters on the solution in the presence of a magnetic field are also presented. The problem is solved covering the entire regime of mixed convection.

TECHNICAL NOTE: NON-DARCY MIXED CONVECTION FROM A HORIZONTAL SURFACE WITH VARIABLE SURFACE HEAT FLUX IN A POROUS MEDIUM

Abstract This article investigates numerically the heat transfer characteristics of non-Darcy mixed convection over a horizontal flat plate with nonuniform surface heat flux in a porous medium. The surface heat flux is assumed to vary as a power of the axial coordinate measured from the leading edge of the plate. The entire regime of mixed convection (including the two limits of pure forced convection and pure free convection) is divided into two regions, namely the forced convection dominated regime and the free convection dominated regime. The effects of flow inertia force, solid boundary shear, near-wall porosity variation, and thermal dispersion are considered in the present analysis. The Darcy-Brink-man-Forchheimer equation is used to model the motion of fluid through the porous medium, and the porosity variation is approximated by an exponential function. The local Nussett numbers, valid for the entire mixed convection regime, are presented for representative values of governing parameters.

MHD MIXED CONVECTION FROM A HORIZONTAL CIRCULAR CYLINDER

This work investigates analytically the effect of a radial magnetic field on the flow and heat transfer characteristics of mixed convection from a horizontal circular cylinder. Variable wall temperature is assumed at the cylinder surface. Two sets of transformations are used, one for forced-convection-dominated flow and the other for buoyancy-convection-dominated flow. The results are obtained numerically using the local nonsimilarity method and the coordinate perturbation method. The variation of local wall shear stress and local heat transfer along the circumference up to the point of separation and the velocity and temperature profiles in the boundary layer are obtained for varying values of the magnetic parameter (Ha2/Re) and the buoyancy parameter (Cr/Re2), which covers the entire regime of mixed convection from the pure forced convection to the pure free convection. It is found that the presence as well as the increase in the magnetic field leads to a decrease in the velocity field, local wall shear stress, and local Nusslet number and a rise in the values of temperature in the flow field.

MHD mixed convection from a vertical cylinder embedded in a porous medium

MHD mixed convection flow about a vertical cylinder embedded in a porous medium is considered using non-Darcian model. Variable heat transfer boundary condition is incorporated. A transformation that enable solving for the entire mixed convection regime is introduced. Results are obtained using a finite difference scheme. The effect of the applied magnetic field on the heat transfer coeffecient and on the wall shear stress is presented for the entire mixed convection regime including pure forced and pure natural convection limits. The magnetic field is found to have different behavior in the forced convection dominated regime other than that in natural convection dominated regime.