Natural Convection Mass Transfer Research Articles

Theoretical analysis of natural convection boundary layer heat and mass transfer of nanofluids: Effects of size, shape and type of nanoparticles, type of base fluid and working temperature

The problem of natural convection boundary layer heat transfer of nanofluids is theoretically analyzed. Different aspects of nanoparticles, such as size, shape and constructive material, as well as the type of the base fluid and the working temperature, are examined. The drift-flux model of nanofluids, including the effects of Brownian motion, thermophoresis, and the local volume fraction of nanoparticles, is adopted to model the boundary layer heat and mass transfer of nanofluids. Following the state-of-the-art, the thermo-physical properties are extracted from five different synthesized types of nanofluids. A new non-dimensional parameter, the enhancement ratio, indicating the ratio of the convective heat transfer coefficient of the nanofluid to the base fluid, is introduced. The effect of the nanoparticles on the enhancement of natural convective heat transfer of nanofluids is discussed. The main findings of this study are as follows: (i) the type of the nanoparticles and the base fluid are the most important parameters affecting the heat transfer of nanofluids; (ii) in some cases, the presence of nanoparticles in the base fluid deteriorates the heat transfer rate; and (iii) the rise of the working temperature reduces the efficiency of the nanofluid, which is a crucial issue in applications of nanofluids as coolants.

LIE GROUP ANALYSIS OF MHD NATURAL CONVECTION HEAT AND MASS TRANSFER FLOW OF A CASSON FLUID OVER AN INCLINED SURFACE WITH CHEMICAL REACTION

Natural convective heat and mass transfer of a non-Newtonian fluid over an inclined surface with uniform magnetic field and chemical reaction has been investigated numerically. The Casson fluid model is used to characterize the nonNewtonian fluid behavior and the first order of chemical reaction is considered. Lie group analysis is employed to obtain the symmetries of the governing system of partial differential equations and they reduce them to a system of ordinary differential equations via scaling transformation. Numerical computations have been carried out using the fourth order Runge–Kutta scheme with shooting techniques with a systematic guessing values of F1´(0), F3´ and F4´(0). The procedure is repeated until we get the results up to the desired degree of accuracy, namely 10-5 .

Natural convection heat and mass transfer in MHD fluid flow past a moving vertical plate with variable surface temperature and concentration in a porous medium

A numerical investigation of two-dimensional steady laminar free convection flow with heat and mass transfer past a moving vertical plate in a porous medium subjected to a transverse magnetic field is carried out. The temperature and concentration level at the plate surface are assumed to follow a power-law type of distribution. The governing non-linear set of equations is solved numerically employing a fully implicit finite difference method. Results are presented to illustrate the influence of different parameters such as Grashof number (Gr), porosity parameter (Kp), magnetic field parameter (Mn) and exponents in the power law variation of the surface temperature and concentration, m and n. The dimensionless velocity, temperature and concentration profiles are analyzed and numerical data for the local Nusselt number and Sherwood number are presented. The study accentuates the significance of the relevant parameters.

A multiscale modeling study for the convective mass transfer in a subsurface aquifer

Quantitative and realistic computer simulations of mass transfer associated with \(\hbox {CO}_2\) disposal in subsurface aquifers is a challenging endeavor. This article has proposed a novel and efficient multiscale modeling framework, and has examined its potential to study the penetrative mass transfer in a \(\hbox {CO}_2\) plume that migrates in an aquifer. Numerical simulations indicate that the migration of the injected \(\hbox {CO}_2\) enhances the vorticity generation, and the dissolution of \(\hbox {CO}_2\) has a strong effect on the natural convection mass transfer. The vorticity decays with the increase of the porosity. The time scale of the vertical migration of a \(\hbox {CO}_2\) plume is strongly dependent on the rate of \(\hbox {CO}_2\) dissolution. Comparisons confirm the near optimal performance of the proposed multiscale model. These primary results with an idealized computational model of the \(\hbox {CO}_2\) migration in an aquifer brings the potential of the proposed multiscale model to the field of heat and mass transfer in the geoscience.

MHD Natural Convection Heat and Mass Transfer of Al2O3-Water and Ag-Water Nanofluids over a Vertical Cone with Chemical Reaction

In this paper, we have presented a numerical solution to the MHD heat and mass transfer flow of a nanofluid through porous media over a vertical cone with heat generation/absorption and chemical reaction. Though we have different varieties of nanofluids, we have considered Al2O3-water and Ag-water based nanofluids (with volume fraction 1% and 4%) in this problem. The transformed conservation equations for the nanofluid are solved numerically subject to the boundary conditions using finite element method. The numerical code is validated with previous studies. The influence of important non-dimensional parameters, namely nanoparticles volume fraction (φ), Prandtl number (Pr), magnetic (M), mixed convection (Ra), buoyancy ratio (Nr), space-dependent (A), temperature-dependent (B) and chemical reaction (Cr) parameters on velocity, temperature and nanoparticle concentration fields as well as the skin-friction coefficient, Nusselt number and Sherwood number are examined in detail and the results are shown in graphically and in tabular form.

Natural Convection Heat and Mass Transfer Flow with Hall Current, Rotation, Radiation and Heat Absorption Past an Accelerated Moving Vertical Plate with Ramped Temperature

Natural Convection Heat and Mass Transfer Flow with Hall Current, Rotation, Radiation and Heat Absorption Past an Accelerated Moving Vertical Plate with Ramped Temperature

Role of thermal diffusion on double-diffusive natural convection in a vertical annular porous medium

Abstract This paper derives analytical solutions of fully developed natural convection heat and mass transfer in a vertical annular non-Darcy porous medium. This investigation extends the work of Cheng (2006) to a situation where Soret effect is present and the flow is both aided and opposed. The influence of the controlling parameters on the flow characteristics has been seen to be higher for double diffusion in the absence of Soret effect than in the presence of Soret effect. It is found that the presence of Soret effect reduces the dependence of the volume flow rate, the total heat rate and the total species rate on the inner radius-gap ratio and on the modified Darcy number.

Double-diffusive natural convection of Al2O3-water nanofluid in an enclosure with partially active side walls using variable properties

Natural convection heat and mass transfer characteristics in a square enclosure using variable thermal conductivity and variable viscosity are numerically studied. The fluid in the enclosure is a water-based nanofluid containing Al2O3 nanoparticles. The top and bottom horizontal walls are insulated, while a source (Th, Ch) and a sink (Tc, Cc) are located at the vertical left and right walls as active parts, respectively, with Th>Tc and Ch>Cc. The governing equations in the two-dimensional space are discretized using the control volume method. A proper upwinding scheme is employed to obtain stabilized solutions. The study has been carried out for the Rayleigh numbers of 104 to 106, the buoyancy ratios of −5∼5, and different configurations of the source and sink. Results are presented in the form of the streamlines, isotherms and iso-concentraions as well as the average Nusselt and Sherwood numbers. It is observed that average Nusselt number is increased by adding the nanoparticles, while average Sherwood number is reduced. Moreover, both Nusselt and Sherwood number are increased as absolute value of the buoyancy ratio or Rayleigh number is increased.

MHD Natural Convection Heat and Mass Transfer Flow Past a Time Dependent Moving Vertical Plate with Ramped Temperature in a Rotating Medium with Hall Effects, Radiation and Chemical Reaction

AbstractAn investigation of unsteady hydromagnetic natural convection heat and mass transfer flow of an electrically conducting, viscous, incompressible and optically thick radiating fluid past an impulsively moving infinite vertical plate embedded in a uniform porous medium in a rotating system with Hall effects in the presence of homogeneous first order chemical reaction is carried out when temperature of the plate has a temporarily ramped profile. Exact solution of the governing equations is obtained in closed form by Laplace transform technique. Expressions for skin friction due to primary and secondary flows and Nusselt number are derived for both ramped temperature and isothermal plates. Expression for Sherwood number is also derived. The numerical values of primary and secondary fluid velocities, fluid temperature and species concentration are displayed graphically whereas those of skin friction are presented in tabular form for various values of pertinent flow parameters. In order to highlight the influence of ramped temperature distribution within the plate on the flow-field, the fluid flow past a ramped temperature plate is compared with the one past an isothermal plate.

State space approach to unsteady magnetohydrodynamics natural convection heat and mass transfer through a porous medium saturated with a viscoelastic fluid

A technique of the state space approach and the inversion of the Laplace transform method are applied to dimensionless equations of an unsteady one-dimensional boundary-layer flow due to heat and mass transfer through a porous medium saturated with a viscoelastic fluid bounded by an infinite vertical plate in the presence of a uniform magnetic field is described. Complete analytical solutions for the temperature, concentration, velocity, and induced magnetic and electric fields are presented. The inversion of the Laplace transforms is carried out by using a numerical approach. The proposed method is used to solve two problems: boundary-layer flow in a viscoelastic fluid near a vertical wall subjected to the initial conditions of a stepwise temperature and concentration and viscoelastic fluid flow between two vertical walls. The solutions are found to be dependent on the governing parameters including the Prandtl number, the Schmidt number, the Grashof number, reaction rate coefficient, viscoelastic parameter, and permeability of the porous medium. Effects of these major parameters on the transport behavior are investigated methodically, and typical results are illustrated to reveal the tendency of the solutions. Representative results are presented for the velocity, temperature, concentration, and induced magnetic and electric field distributions, as well as the local skin-friction coefficient and the local Nusselt and Sherwood numbers.

A BINARY CHEMICAL REACTION ON UNSTEADY FREE CONVECTIVE BOUNDARY LAYER HEAT AND MASS TRANSFER FLOW WITH ARRHENIUS ACTIVATION ENERGY AND HEAT GENERATION/ABSORPTION

We investigate a local similarity solution of an unsteady natural convection heat and mass transfer boundary layer incompressible fluid flow past a moving vertical porous plate in the presence of the heat absorption and generation. The effects of chemical reaction rate which is function of temperature and Arrhenius activation energy on the velocity, temperature and concentration are also studied in this paper. The governing partial differential equations are reduced to ordinary differential equations by introducing local similarity transformation (Maleque, 2010a). Numerical solutions to the reduced non-linear similarity equations are then obtained by adopting Runge-Kutta and shooting methods using the Nachtsheim- Swigert iteration technique. The results of the numerical solution are then presented graphically in the form of velocity, temperature and concentration profiles. The corresponding skin friction coefficient, the Nusselt number and the Sherwood number are also calculated and displayed in table showing the effects of various parameters on them.

Unsteady Natural Convective Flow Over an Impulsively Started Semi-Infinite Vertical Plate in the Presence of Porous Medium

The fundamental study of the phenomenon of natural convective heat and mass transfer near a vertical plate in the presence of porous medium is investigated. The fluids considered in the discussion are air and water. The unsteady, coupled, non-linear partial differential equations are solved numerically by Crank Nicolson scheme. The influence of various parameters like velocity, temperature and concentration are analyzed. The skin friction, the Nusselt number, the Sherwood number, average skin friction, average Nusselt number and average Sherwood number are also presented graphically for both air and water. It has been observed that velocity components increase with permeability parameter where as temperature and concentration decreases with it. An analysis is performed to check the stability and the convergence of the finite difference scheme which converges faster and unconditionally stable.

FREE CONVECTIVE MASS TRANSFER BEHAVIOR OF FINNED TUBES

Rates of natural convective mass transfer at vertical and horizontal finned cylinders were determined by an electrochemical technique that involved measuring the limiting current of the cathodic deposition of copper from acidified copper sulfate solution. Variables studied were fin spacing (s), fin diameter (d), and physical properties of the solution. For vertical and horizontal finned tubes it was found that the mass transfer coefficient increases with increasing fin height and decreases with increasing fin separation. Rates of mass transfer at vertical and horizontal finned tubes were found to be higher than that at unfinned (plain) tubes by an amount ranging from 44% to 96%. Although the degree of mass transfer enhancement by fins is higher at vertical cylinders, horizontal finned cylinders have higher mass transfer coefficients than vertical finned cylinder under the same conditions. Mass transfer data at vertical finned cylinders were correlated by the equation while mass transfer data at horizontal finned cylinders were correlated by the equation Implications of the present study for determining the rate of diffusion-controlled metal finishing processes that are conducted during the fabrication of finned tubes such as electroplating, electroless plating, etching, electro-polishing, and pickling were noted. Also, the importance of the present results for design and operation of electrochemical reactors fitted with fins (baffles) was highlighted. The possibility of using the derived equations in predicting rates of heat transfer in solutions of high Pr by analogy with mass transfer was outlined.

Effects of Hall current, radiation and rotation on natural convection heat and mass transfer flow past a moving vertical plate

An investigation of the effects of Hall current and rotation on unsteady hydromagnetic natural convection flow with heat and mass transfer of an electrically conducting, viscous, incompressible and optically thick radiating fluid past an impulsively moving vertical plate embedded in a fluid saturated porous medium, when temperature of the plate has a temporarily ramped profile, is carried out. Exact solution of the governing equations is obtained in closed form by Laplace transform technique. Exact solution is also obtained in case of unit Schmidt number. Expressions for skin friction due to primary and secondary flows and Nusselt number are derived for both ramped temperature and isothermal plates. Expression for Sherwood number is also derived. The numerical values of primary and secondary fluid velocities, fluid temperature and species concentration are displayed graphically whereas those of skin friction are presented in tabular form for various values of pertinent flow parameters.

Analysis of the characteristics of heat and mass transfer of a three-effect tubular solar still and experimental research

A self-made solar-powered or residual heat-powered three-effect tubular solar still is used to analyze the characteristics of heat and mass transfer and study on normal-pressure and fixed-temperature heating in and fixed-power heating, attempting to figure out the principles of heat and mass transfer as well as the parameters of water production by desalination. The interior heat and mass transfer of still is consistent with three-effect energy equilibrium formula, the process of which mainly includes natural convection mass transfer and radiation heat exchange. The experimental results show that there exists a direct-proportion linear relationship between the temperature and water production by desalination at normal pressure, that at negative pressure, the water production is several times as large as that at normal pressure, increasing with the decrease of interior pressure, and reaching as high as 1.12kg/h when the temperature is at 80°C and the interior pressure is close to the saturation vapor pressure of 50kPa at the first level, and that the water yield by desalination increases as the heating power (<300W) increases, the optimal heating power is 300W and its corresponding performance ratio reaches the highest value of 1.3.

Natural convection heat and mass transfer from a sphere in non-Newtonian nanofluids

A boundary layer analysis has been presented for the natural convection flow of a non-Newtonian nanofluid past a sphere. Solutions of the set of nonsimilarity equations are obtained by employing the implicit finite difference method together with Keller box elimination method. Numerical results for friction factor, surface heat transfer rate and mass transfer rate have been presented for parametric variations of the material parameters, buoyancy ratio parameter [Formula: see text], Brownian motion parameter NB, thermophoresis parameter NT and Schmidt number Sc. The dependency of the surface heat transfer rate (Nusselt number) and mass transfer rate on these parameters has been discussed. It was found that the heat transfer rate decreases and mass transfer rates increase as Schmidt number increases. The friction factor and heat transfer rates decrease as the cross viscosity parameter [Formula: see text] increases. The heat transfer rates increase and mass transfer rates decrease as the buoyancy ratio parameter N increases. As the thermophoresis parameter NT increases, the heat and mass transfer rates increase. As the Brownian parameter NB increases, the heat and mass transfer rates decrease. Brownian motion decelerates the flow in the nanofluid boundary layer. Brownian diffusion promotes heat conduction. The Brownian motion and thermophoresis of nanoparticles increase the effective thermal conductivity of the nanofluid. Both Brownian diffusion and thermophoresis give rise to cross diffusion terms that are similar to the familiar Soret and Dufour cross diffusion terms that arise with a binary fluid.

Natural Convection Heat and Mass Transfer in a Micropolar Fluid with Thermal and Mass Stratification

The effects of thermal and solutal stratification on natural convection along a vertical plate embedded in a micropolar fluid are analyzed in both cases of buoyancy-assisting and buoyancy-opposing flows. The nonlinear governing equations and their associated boundary conditions are initially cast into dimensionless forms by pseudo-similarity variables. The resulting system of equations is then solved numerically using the Keller-box method. The numerical results are compared and found to be in good agreement with previously published results as special cases of the present investigation. The velocity, microrotation, temperature, and concentration profiles are shown for different values of the coupling number, thermal, and solutal stratification parameters. The numerical values of the skin friction, wall couple stress, heat and mass transfer rates for different values of governing parameters are also tabulated.

Effects of Exothermic/Endothermic Chemical Reactions with Arrhenius Activation Energy on MHD Free Convection and Mass Transfer Flow in Presence of Thermal Radiation

A local similarity solution of unsteady MHD natural convection heat and mass transfer boundary layer flow past a flat porous plate within the presence of thermal radiation is investigated. The effects of exothermic and endothermic chemical reactions with Arrhenius activation energy on the velocity, temperature, and concentration are also studied in this paper. The governing partial differential equations are reduced to ordinary differential equations by introducing locally similarity transformation (Maleque (2010)). Numerical solutions to the reduced nonlinear similarity equations are then obtained by adopting Runge-Kutta and shooting methods using the Nachtsheim-Swigert iteration technique. The results of the numerical solution are obtained for both steady and unsteady cases then presented graphically in the form of velocity, temperature, and concentration profiles. Comparison has been made for steady flow () and shows excellent agreement with Bestman (1990), hence encouragement for the use of the present computations.

Natural convection of nanofluid over vertical plate embedded in porous medium: prescribed surface heat flux

The aim of the present paper is to analyze the natural convection heat and mass transfer of nanofluids over a vertical plate embedded in a saturated Darcy porous medium subjected to surface heat and nanoparticle fluxes. To carry out the numerical solution, two steps are performed. The governing partial differential equations are firstly simplified into a set of highly coupled nonlinear ordinary differential equations by appropriate similarity variables, and then numerically solved by the finite difference method. The obtained similarity solution depends on four non-dimensional parameters, i.e., the Brownian motion parameter (N b), the Buoyancy ratio (N r), the thermophoresis parameter (N t), and the Lewis number (Le). The variations of the reduced Nusselt number and the reduced Sherwood number with N b and N t for various values of Le and N r are discussed in detail. Simulation results depict that the increase in N b, N t, or N r decreases the reduced Nusselt number. An increase in the Lewis number increases both of the reduced Nusselt number and the Sherwood number. The results also reveal that the nanoparticle concentration boundary layer thickness is much thinner than those of the thermal and hydrodynamic boundary layers.

English

The entropy generation for natural convection heat and mass transfer in a two dimensional porous cavity subjected to a magnetic field is selected for numerical investigation. The Darcy model is used in the mathematical formulation of the fluid flow in porous media. The mathematical model is derived in dimensionless form and the governing equations are solved using the finite volume method. The governing parameters arise in the mathematical model are the Rayleigh number, Lewis number, buoyancy ratio and Hartmann number. The results are presented as&nbsp;average Nusselt number (), Sherwood numbers () and&nbsp;dimensionless form of local entropy generation rate (Ns) for different values of the governing parameters.&nbsp;&nbsp;The numerical results show that increasing the magnetic field parameter (Hartmann number) leads to deterioration of the flow circulation strength in the cavity and this leads to a decrease in the rates of the heat and mass transfer as well as the rate of entropy generation. The results show a stagnate fluid everywhere in the cavity when the buoyancy forces generated due to temperature and concentration differences are in the same order and opposite directions. In this case, the values of&nbsp;,&nbsp;&nbsp;and&nbsp;Ns&nbsp;are the minimum. Increasing or decreasing the value of the buoyancy ratio parameter leads to enhance the fluid circulation and hence increase the values of&nbsp;,&nbsp;&nbsp;and&nbsp;Ns. The average Sherwood number can be increased with increasing Lewis number. It is observed that the strength of the fluid circulation in the cavity is reduced by increasing the Lewis number. This leads to the decrease in the average Nusselt number and the entropy generation by increasing Lewis number. Key words:&nbsp;Natural convection, mass transfer, entropy generation, magnetic field, porous media.