Showing papers on "Combined forced and natural convection published in 2014"

Mixed convection of copper-water nanofluid in a shallow inclined lid driven cavity using the lattice Boltzmann method

Abstract: The goal of this work is to study the laminar mixed convection of water–Cu nanofluid in an inclined shallow driven cavity using the lattice Boltzmann method. The upper lid of the cavity moves with constant velocity, U 0 , and its temperature is higher than that of the lower wall. The side walls are assumed to be adiabatic. The effects of different values of the cavity inclination angle and nanoparticles volume fraction at three states of free, force and mixed convection domination are investigated while the Reynolds number is kept fixed as Re = 100 and Re = 10 . Validation of present results with those of other available ones shows a suitable agreement. Streamlines, isotherms, Nusselt numbers, and velocity and temperature profiles are presented. More Nusselt numbers can be achieved at larger values of the inclination angle and nanoparticles volume fraction at free convection domination. Results imply the appropriate ability of LBM to simulate the mixed convection of nanofluid in a shallow inclined cavity.

Comparison of the Finite Volume and Lattice Boltzmann Methods for Solving Natural Convection Heat Transfer Problems inside Cavities and Enclosures

Abstract: Different numerical methods have been implemented to simulate internal natural convection heat transfer and also to identify the most accurate and efficient one. A laterally heated square enclosure, filled with air, was studied. A FORTRAN code based on the lattice Boltzmann method (LBM) was developed for this purpose. The finite difference method was applied to discretize the LBM equations. Furthermore, for comparison purpose, the commercially available CFD package FLUENT, which uses finite volume Method (FVM), was also used to simulate the same problem. Different discretization schemes, being the first order upwind, second order upwind, power law, and QUICK, were used with the finite volume solver where the SIMPLE and SIMPLEC algorithms linked the velocity-pressure terms. The results were also compared with existing experimental and numerical data. It was observed that the finite volume method requires less CPU usage time and yields more accurate results compared to the LBM. It has been noted that the 1st order upwind/SIMPLEC combination converges comparatively quickly with a very high accuracy especially at the boundaries. Interestingly, all variants of FVM discretization/pressure-velocity linking methods lead to almost the same number of iterations to converge but higher-order schemes ask for longer iterations.

Effect of nanofluid variable properties on mixed convection flow and heat transfer in an inclined two-sided lid-driven cavity with sinusoidal heating on sidewalls

Abstract: In this study, mixed convection fl uid fl ow and heat transfer in an inclined two-sided lid-driven cavity subjected to Al2O3–water nanofl uid (with diff erent particle diameters from 15 to 99 nm) has been investigated numerically. The geometry is a double lid-driven square cavity with sinusoidal temperature distribution on the left sidewall, while the right wall is kept at Tc. The top and bott om walls of the cavity, which move in opposite directions, are assumed to be insulated. The eff ects of inclination angle, Richardson number, nanoparticle volume fraction, temperature, and nanoparticle diameter based on recent variable property formulations are studied. The eff ects of an increase in Richardson number while the solid volume fraction is constant and eff ects of an increase in solid volume fraction when the Richardson number is kept constant are investigated. Also, the obtained results show that an increase in nanoparticle diameter infl uences the fl ow patt ern and isotherm contours inside the cavity relatively when the Richardson number is kept constant and the diameter is varied from 15 to 99 nm. As the mean nanoparticle diameter increases, the corresponding fl ow velocity decreases, and hence the heat transfer enhancement is reduced. The results indicate that as Richardson number increases, the average Nusselt number rapidly increases for diff erent values of dp. Moreover, the results have clearly indicated that the addition of Al2O3 nanoparticles has produced a remarkable enhancement on heat transfer with respect to that of the pure fl uid.

MHD mixed convection of nanofluid filled partially heated triangular enclosure with a rotating adiabatic cylinder

Abstract: MHD mixed convection of Cu–water nanofluid filled triangular enclosure with a rotating cylinder is investigated numerically. A partial heater is added on the left vertical wall of the cavity and the right inclined wall is kept at constant temperature. Other walls of the triangular cavity and cylinder surface are assumed to be adiabatic. The governing equations are solved using the finite element method. The effects of the Grashof number, Hartmann number, angular rotational speed of the cylinder and volume fraction of the nanoparticle on fluid flow and heat transfer are investigated numerically. The second law of thermodynamics is also applied to the flow and heat transfer corresponding to different combinations of parameters. It is observed that with increasing the Hartmann number the total entropy generation, local and averaged heat transfer decrease. Averaged Nusselt number increases with the Grashof number. Averaged heat transfer and total entropy generation increase with increase in the angular rotational speed of the cylinder. 50.4% and 37.4% of heat transfer enhancements are obtained for ω = 20 and ω = −20 compared to motionless cylinder ω = 0. Heat transfer and total entropy generation increase as the solid volume fraction of nanoparticle increases.

Thermophoresis particle deposition in mixed convection three-dimensional radiative flow of an Oldroyd-B fluid

Abstract: This article describes heat and mass transfer characteristics in three-dimensional flow of an Oldroyd-B fluid. The flow caused is due to bidirectional stretching surface. Radiation effects are taken into account via Rosseland approximation. In addition the thermophoresis effects are considered. Results of velocities, temperature and concentration are constructed. The obtained results are plotted and discussed for interesting physical parameters. We have seen that the increasing values of thermophoretic parameter leads to a decrease in the concentration field and concentration boundary layer thickness. Also it is noticed that the concentration field corresponding to thermophoretic parameter decays quickly in comparison to concentration field for Schmidt number.

Unsteady Heat and Mass Transfer by MHD Mixed Convection Flow From a Rotating Vertical Cone With Chemical Reaction and Soret and Dufour Effects

Abstract: This work focused on the study of Soret and Dufour effects on unsteady coupled heat and mass transfer by mixed convection flow over a vertical cone rotating in an ambient fluid with a time-dependent angular velocity in the presence of a magnetic field and chemical reaction. The cone surface is maintained at variable temperature and concentration. The resulting governing equations are non-dimensionalised and transformed into a non-similar form and then solved numerically by an implicit, iterative, finite-difference method. Comparisons with previously published work are performed and excellent agreement is obtained. A parametric study showing the effects of the buoyancy parameter, magnetic field, chemical reaction parameter, Soret and Dufour numbers on the local tangential and azimuthal skin friction coefficients, and the local Nusselt and Sherwood numbers are conducted. These results are illustrated graphically to depict special features of the solutions.

Numerical investigation on mixed convective peristaltic flow of fourth grade fluid with Dufour and Soret effects

Abstract: Heat and mass transfer analysis in the mixed convective peristaltic flow of fourth-grade fluid under viscous dissipation, Dufour and Soret effects is carried out Mathematical model is formulated by incorporating long wavelength and low Reynolds number assumptions The resulting coupled nonlinear boundary value problem (BVP) has been solved numerically by Keller–box method The computations are validated through the built in routine for solving nonlinear boundary value problems via shooting method through the software Mathematica The results indicate an increase in the pumping rate and a decrease in the temperature and concentration functions with an increase in the elastic parameter (Deborah number) for fourth grade fluid The temperature and concentration are increasing functions of the buoyancy forces due to temperature and concentration gradients