Asymmetric Wall Temperatures Research Articles

New Investigation of Asymmetric Wall Temperature and Fluid-Wall Interaction on Radiative Steady MHD Fully Developed Natural Convection in Vertical Micro-Porous–Channel

New Investigation of Asymmetric Wall Temperature and Fluid-Wall Interaction on Radiative Steady MHD Fully Developed Natural Convection in Vertical Micro-Porous–Channel

Investigation of asymmetric wall temperature and concentration on free convection of conducting fluid in a microchannel

AbstractIt is of great practical interest to study the fluid flow phenomena using buoyancy‐induced flow in a microchannel. The present problem is concerned with the natural convection in a vertical microchannel within electrically nonconducting surfaces with asymmetric wall temperature and concentration distributions. The interplay of velocity slip, temperature, and concentration jump at the walls contribute to salient features of the analysis. The governing equations of the fully developed flow are solved analytically as well as numerically. The results of both methods are in good agreement, providing the consistency and reliability of the applied numerical method. The striking outcome of the present study is that temperature, as well as concentration jump conditions at the walls, lead to flow reversal and non‐laminarity distributions of the induced current intensity and magnetic field. The higher rarefaction parameter, which ascribes the microchannel flow characteristics, prevents the growth of negative current intensity, whereas it favors the growth of velocity with induced magnetization.

Variable Viscosity and Thermal Conductivity Effects on Entropy Generation in Nanofluid Flow in an Inclined Channel: HAM Solution

This work investigates the entropy generation in nanofluid flow in a sloping channel with Navier slip and asymmetric wall temperatures. The viscosity and thermal conductivity are assumed to be dependent on temperature. The equations governing the flow, temperature are nonlinear and are solved using Homotopy Analysis Method (HAM) after non-dimensionalisation. Comparisons with existing literature have been produced and are found to be in excellent agreement, for special case of the current formulation. The impact of pertinent flow and fluid parameters on entropy generation, Bejan number, Nusselt number and skin friction is addressed, developed and displayed graphically.

Mixed Convection between Horizontal Parallel Plates.(Dept.M)

In the present study laminar mixed convection between two horizontal parallel lates kept at symmetric and asymmetric Uniform wall temperatures is studied. The momentum and energy equations are transformed to a dimensionless form by introducing appropriate dependent and independent variables and a dimensionless temperature ratio The local similarity solution method is implemented to transform the governing equations to a system of ordinary differential equations. The locally similar equations are solved numerically by the Runge--Kutta integration technique along with the Newton-Raphson shooting method at different axial locations over the range of the mixed convection parameter 0. 01 5 ≤ ζ ≤ 0.1. Results are obtained for thelocal heat transfer. coefficient of friction. and velocity and temperature distributions. Effect of the mixed convection parameter, the configuration parameter. Prandtl number and the temperature ratio are studied.

DynamFluid: Development and Validation of a New GUI-Based CFD Tool for the Analysis of Incompressible Non-Isothermal Flows

A computational fluid dynamics software (DynamFluid) based on the application of the finite element method with the characteristic-based-split algorithm is presented and validated. The software is used to numerically integrate the steady and unsteady Navier–Stokes equations for both constant-density and Boussinesq non-isothermal flows. Benchmark two-dimensional computations carried out with DynamFluid show good agreement with previous results reported in the literature. Test cases used for validation include (i) the lid-driven cavity flow, (ii) mixed convection flow in a vertical channel with asymmetric wall temperatures, (iii) unsteady incompressible flow past a circular cylinder, and (iv) steady non-isothermal flow past a circular cylinder with negligible buoyancy effects. The new software is equipped with a graphical user interface that facilitates the definition of the fluid properties, the discretization of the physical domain, the definition of the boundary conditions, and the post-processing of the computed velocity, pressure and temperature fields.

Soret effects on the mixed convection flow using Robin boundary conditions

AbstractAn investigation has been undertaken as Soret and Schmidt outcomes on the mixed convection flow using Robin boundary conditions. The results use a vertical channel being kept at constant cold temperature and concentration at the left wall and hot temperature and concentration at the right wall. The exchange of heat is done by help of plates with a fluid. We consider the external fluid with equal and different temperatures. This physical problem is solved by using nondimensional parameters with the corresponding boundary conditions. To find analytical solution, the regular perturbation series method is used, and for finding the numerical solution, the well‐known Runge–Kutta method with shooting technique is employed. Comparison of the current study is favorable with the previous published results. The obtained results depend on the governing parameters such as thermal Grashof number, solutal Grashof number, Biot numbers, symmetric and asymmetric wall temperatures, Schmidt number, Soret number, and Brinkman number. An influence of these parameters on the fields of velocity, temperature, and concentration is reported. Further, the numerical results for the Nusselt number, mean value of the velocity, dimensionless bulk temperature, skin friction, and molecular diffusion coefficient are tabulated for different parametric conditions and explained. For small value of Brinkman number, the obtained values agree with other published results for all considered cases.

Effect of viscous dissipation on mixed convection flow in a vertical double passage channel using Robin boundary conditions

The laminar fully developed flow in a vertical double passage channel filled with clear fluid has been discussed using Robin boundary conditions. The thin perfectly conductive baffle is inserted in the channel. The governing equations of the fluid which are coupled and nonlinear are solved analytically by the perturbation method and semi analytically using differential transform method (DTM). The reference temperature of the external fluid is considered to be equal and different. The perturbation method which is valid for small values of perturbation parameter is used to find the combined effects of buoyancy forces and viscous dissipation. The limitation imposed on the perturbation parameter is relaxed by solving the basic equations using differential transform method. The influence of mixed convection parameter, Biot number for symmetric and asymmetric wall temperatures on the velocity, temperature and the Nusselt number is explored at different positions of the baffle. The solutions obtained by differential transform method are justified by comparing with the solutions obtained by perturbation method and the solutions agree very well for small values of the perturbation parameter.Keywords: Baffle, Differential Transform Method, Perturbation Method, Viscous dissipation, Robin Boundary Conditions, Double passage channel.

Analytical and experimental studies for power-law fluids in a double-pass parallel-plate heat exchanger under asymmetric isotherm conditions

The double-pass parallel-plate heat exchanger under asymmetric isotherm conditions referred to conjugated Graetz problem was proposed to enhance the thermal performance and investigated theoretically and experimentally. The analytical solutions were obtained using the separation of variables, superposition principle and an orthogonal expansion technique in terms of power series. The dependence of the average Nusselt number on the Graetz number and power-law index was formulated in a simplified expression. The theoretical predictions show that the power-law fluids in such a double-pass operation come up with the considerable heat-transfer efficiency improvement as compared with those in an open conduit (without an impermeable resistless sheet inserted), especially when the double-pass device was operated in larger Graetz numbers. This work shows that the good agreement was obtained between the experimental results and theoretical predictions. The effects of the ratio of asymmetric wall temperatures, impermeable-sheet position and power-law index on both the device performance enhancement and power consumption increment have also been presented.

Recycle effect on heat transfer enhancement in double-pass heat exchangers under asymmetric isotherm conditions

The mathematical formulation of a heat transfer flow problem in the recycling parallel-plate heat exchanger under asymmetric wall temperatures was developed theoretically with ignoring axial conduction, and the analytical solution was obtained using a superposition principle and an orthogonal expansion technique in extended power series. The influences of the design parameters of the impermeable-sheet position (∆), and the operating parameters of the Graetz number (Gz), wall temperature ratio (σ) and recycle ratio (R) are examined. Significant heat transfer improvement is obtainable by employing double-pass devices instead of using single-pass ones for a larger Graetz number system. A technical feasibility of the new double-pass device was investigated in terms of the Nusselt number and device performance improvement under the effect of wall temperature ratios.

Free Convection Heat and Mass Transfer MHD Flow in a Vertical Porous Channel in the Presence of Chemical Reaction

The objective of the present study is to examine the fully developed free convective MHD flow of an electrically conducting viscous incompressible fluid in a vertical porous channel under influence of asymmetric wall temperature and concentration in the presence of chemical reaction. The heat and mass transfer coupled with diffusion-thermo effect renders the present analysis interesting and curious. The analytical solution by Laplace transform technique of partial differential equations is used to obtain the expressions for the velocity, temperature, and concentration. It is observed that under the influence of dominating mass diffusivity over thermal diffusivity with stronger Lorentz force the velocity is reduced at all points Further, low rate of thermal diffusion delays the attainment of free stream state. Flow of aqueous solution in the presence of heavier species is prone to back flow.

Effects of Thermal‐Diffusion, Diffusion‐Thermo, and Space Porosity on MHD Mixed Convective Flow of Micropolar Fluid in a Vertical Channel with Viscous Dissipation

This paper examines thermal‐diffusion and diffusion‐thermo effects on the fully developed MHD flow of a micropolar fluid through a porous space in a vertical channel with asymmetric wall temperatures and concentrations. The homotopy analysis method (HAM) is adopted to obtain the approximate analytical solution for the velocity, micro‐rotation, temperature, and concentration field. The convergence and the accuracy of the solutions are discussed. The role of pertinent parameters on the heat and mass transfer characteristics of the flow are presented graphically. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(6): 561–576, 2014; Published online 11 November 2013 in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21100

Heat transfer modeling of conjugated Graetz problems in double-pass parallel-plate heat exchangers under asymmetric wall temperatures

The heat transfer of a Graetz problem is investigated theoretically. The problem involves an improvement to the design of a parallel-plate heat exchanger using an inserted plate which forms a double-pass device with recycle operation. The parallel plates are at different temperatures. The theoretical mathematical model is solved analytically using the separation of variables, superposition principle, and an orthogonal expansion technique in extended power series. Significant heat transfer improvement can be realized by the design compared to a single-pass device. The improvement is greater for a larger Graetz number system. For a small Graetz number system, the single-pass design is preferred. The optimal location of the inserted plate is when the two subchannels are at the same height.

Second-Order Mixed Convective Flow in a Long Vertical Microchannel

The present investigation is concerned with the role of second-order slip in the mixed convection through a long heated vertical planar microchannel with asymmetric wall temperatures. The fully developed solutions of fields and the corresponding characteristics are analytically derived on the basis of second-order Maxwell–Smoluchowski–Burnett (MSB) slip/jump boundary conditions. Results reveal that second-order slip has an appreciable effect on the flow but a negligible effect on the heat transfer. The effect is to raise the gas motion speeds near the heated walls and to enlarge the pressure gradient required to drive the flow. It then leads to the reduction of local flow drag, except for the case where a reversed flow region exists. The second-order effect could be magnified by increasing the mixed convection number, the ratio of the Grashof number to the Reynolds number.

Transient magneto-micropolar free convection heat and mass transfer through a non-Darcy porous medium channel with variable thermal conductivity and heat source effects

The laminar, fully developed, transient magnetohydrodynamic (MHD) free convection heat and mass transfer of an electrically conducting micropolar fluid between two vertical plates containing a non-Darcy porous medium with heat generation/absorption and asymmetric wall temperature and concentration has been discussed in this article. A similarity transformation is used to render the problem into a system of coupled, partial, differential equations, which are solved using the finite-element method (FEM). The solutions are validated with a robust finite difference method (FDM) solver. The present work examines the effect of Darcian parameter, Forchheimer parameter, heat absorption/generation parameter, vortex viscosity parameter, buoyancy ratio parameter, magnetic parameter, and variable thermal conductivity parameter on velocity, angular velocity, temperature and concentration profiles. Space—time graphs of velocity and microrotation are also plotted to provide a better perspective of the flowfield evolution with respect to time. Applications of the study may arise in, for example, packed-bed chemical reactors, materials processing, magnetic field control of chemical engineering transport processes in filter media, purification of hydrocarbons with electromagnetic fields, etc.

Fully Developed Free Convection Heat and Mass Transfer of a Micropolar Fluid Between Porous Vertical Plates

In this article, we consider the problem of fully developed natural convection heat and mass transfer of a micropolar fluid between porous vertical plates with asymmetric wall temperatures and concentrations. The resulting boundary-value problem is solved analytically by the homotopy analysis method (HAM). Profiles for velocity and microrotation are presented for a range of values of the Reynolds number and the micropolar parameter.

Solution of fully developed free convection of a micropolar fluid in a vertical channel by homotopy analysis method

AbstractIn this paper, we reconsider the problem of fully developed natural convection heat and mass transfer of a micropolar fluid in a vertical channel with asymmetric wall temperatures and concentrations. The resulting boundary‐value problem is solved analytically by the homotopy analysis method. The accuracy of the present solution is found to be in excellent agreement with the solutions of Cheng (Int. Commun. Heat Mass Transfer 2006; 33:627–635). Copyright © 2008 John Wiley & Sons, Ltd.

Variable Physical Properties in Natural Convective Gas Microflow

Anisothermal flow prevails in a heated microchannel. It is desirable to understand the influence of temperature-dependent physical properties on the flow and heat transfer characteristics for natural convective gas microflow. In this study, formulas for the shear viscosity, thermal conductivity, constant-pressure specific heat, density, and molecular mean free path are proposed in power-law form and validated through experimental data. Natural convective gas flow with variable physical properties in a long open-ended vertical parallel-plate microchannel with asymmetric wall temperature distributions is further investigated. The full Navier–Stokes equations and energy equation combined with the first-order slip∕jump boundary conditions are employed. Analysis process shows that the compressibility and viscous dissipation terms in balance equations are negligible. Numerical solutions are presented for air at the standard reference state with complete accommodation. It is found that the effect of variable properties should be considered for hotter-wall temperatures greater than 306.88K. The effect is to advance the velocity slip and temperature jump as well as the velocity symmetry and temperature nonlinearity. Moreover, it tends to reduce the mass flow rate and the local heat transfer rate excluding on the cooler-wall surface where the temperature-jump effect prevails over the temperature-nonlinearity effect. Increasing the cooler-wall temperature magnifies the effect on flow behavior but minifies that on thermal behavior.

Developing natural convection with thermal creep in a vertical microchannel

Thermal creep occurs in anisothermal gas microflow. It is highly desirable to understand the creep effect on the flow and heat transfer characteristics for developing natural convective microflow. In this study, we investigate the steady developing natural convective flow in an open-ended vertical parallel-plate microchannel with asymmetric wall temperature distributions. The boundary-layer equations subject to the boundary conditions with respect to dynamic pressure at the channel entry as well as higher-order jump temperature and slip velocity with thermal creep along the channel surface are employed. The mathematical model and the numerical code are validated through available macroscale work. Numerical solutions of high-order slip coefficient, slip/jump, velocity, pressure, temperature, flow rate, flow drag and heat transfer rate are presented for air at the standard reference state with complete accommodation. It is found that thermal creep has significant effect on the high-order slip effect and the flow and thermal fields. The creep effect is to increase the flow rate; moreover, valuable reduced flow drag and enhanced heat transfer are obtained.

Fully-developed heat transfer in annuli with viscous dissipation

For Newtonian concentric annular flows analytical solutions are obtained under imposed asymmetric constant wall heat fluxes as well as under imposed asymmetric constant wall temperatures, taking into account viscous dissipation and for fluid dynamic and thermally fully-developed conditions. Results for the special case of the heat flux ratio for identical wall temperatures and the critical Brinkman numbers marking changes of sign in wall heat fluxes are also derived. Equations are presented for the Nusselt numbers at the inner and outer walls, bulk temperature and normalised temperature distribution as a function of all relevant non-dimensional numbers. Given the complexity of the derived equations, simpler exact expressions are presented for the Nusselt numbers for ease of use, with their coefficients given in tables as a function of the radius ratio.

Fully developed natural convection heat and mass transfer in a vertical annular porous medium with asymmetric wall temperatures and concentrations

This work examines the effects of the modified Darcy number, the buoyancy ratio and the inner radius-gap ratio on the fully developed natural convection heat and mass transfer in a vertical annular non-Darcy porous medium with asymmetric wall temperatures and concentrations. The exact solutions for the important characteristics of fluid flow, heat transfer, and mass transfer are derived by using a non-Darcy flow model. The modified Darcy number is related to the flow resistance of the porous matrix. For the free convection heat and mass transfer in an annular duct filled with porous media, increasing the modified Darcy number tends to increase the volume flow rate, total heat rate added to the fluid, and the total species rate added to the fluid. Moreover, an increase in the buoyancy ratio or in the inner radius-gap ratio leads to an increase in the volume flow rate, the total heat rate added to the fluid, and the total species rate added to the fluid.