Air movement can be utilized to increase the thermal comfort within the building. Microclimatic zones are created within a building due to air movement, radiation, relative humidity and temperature. Free CONVECTION is one of the factors affecting air movement and can thus be used for improving the comfort level. This paper examines the velocity of air movement as a function of the difference in temperature an opening height. It further explains the factors affecting air movement speed and thermal comfort.

Present study proposes a new multidimensional artificially characteristic-based (MACB) scheme for simulation of combined CONVECTION flows. Multidimensional characteristic structure for energy propagation in incompressible flow is derived for the first time. Four pseudo-waves are selected and equations are discretized along them to observe the physical behavior of domain. Viscous fluxes are computed by variables derivatives at the cell interfaces and for time discretization, a 4th-order Runge-Kutta method was used. According to the new scheme, two-dimensional flow with heat transfer in a square cavity and forced CONVECTION around a circular cylinder are solved for a wide range of Reynolds and Grashof numbers. Also, for comparison purposes, the CB scheme with averaging for energy equation is used. It was found that MACB has remarkable faster convergence in comparison with CB scheme and averaging methods. Also, by using MACB scheme, maximum permissible CFL number can be increased 80 percent in comparison to CB scheme. At higher Richardson numbers, the conventional flux averaging was failed to converge properly while MACB scheme presents the most rapid convergence. The computed results of MACB scheme are in good agreement with the benchmark solutions.

The influence of rheological behavior on the natural CONVECTION in a dielectric nanofluid with vertical AC electric field is investigated. The rheology of the nanofluid is described by Maxwell model for calculating the shear stresses from the velocity gradients. The employed model introduces the combined effects of movement of the molecules of the fluid striking the nanoparticles, thermophoresis and electrophoresis due to embedded nanoparticles. The exact solutions of the eigen model value problem for stress-free bounding surfaces are obtained analytically using one term Galerkin method to find the thermal Rayleigh number for onset of both non-oscillatory (stationary) and oscillatory motions. It is found that the oscillatory modes are possible for both bottom and top-heavy distributions of nanoparticles. It is observed that the value of critical Rayleigh number is decreased by a substantial amount with the increase in electric field intensity, whereas role of viscoelasticity (time relaxation parameter) is to hasten the occurence of oscillatory modes appreciably. The thermal Prandtl number is found to delay the occurence of oscillatory modes. These results are also shown graphically.

The problem of steady, laminar and incompressible natural CONVECTION flow in an octagonalenclosure was studied. In this investigation, two horizontal walls were maintained at a constant hightemperature, two vertical walls were kept at a constant low temperature and all inclined walls wereconsidered adiabatic. The enclosure was assumed to be filled with a Bousinessq fluid. The studyincludes computations for different Prandtl numbers Pr such as 0.71, 7, 20 and 50 whereas the Rayleighnumber Ra was varied from 103 to 106. The pressure-velocity form of Navier-Stokes equations andenergy equation was used to represent the mass, momentum and energy conservations of the fluidmedium in the enclosure. The governing equations and boundary conditions were converted todimentionless form and solved numerically by penalty finite element method with discretization bytriangular mesh elements. Flow and heat transfer characteristics were presented in terms of streamlines, isotherms and average Nusselt number Nu. Results showed that the effect of Ra on the CONVECTION heattransfer phenomenon inside the enclosure was significant for all values of Pr studied (0.71-50). It wasalso found that, Pr influence natural CONVECTION inside the enclosure at high Ra (Ra > 104).

In this paper pin-fin cooling by mixed CONVECTION has been considered. The system consisting of a pin-fin heat sink and a chimney is presented for increasing heat transfer and draft force. The flow regime is laminar. The results is applied to problems in which the size of the overall system is constrained. For a given heat dissipation and total system size optimal values of the pin-fin diameter and heat sink porosity are obtained. It is shown hat the optimum occur for systems with and without chimney. The pin-fin array is modeled as a Forchheimer-flow porous medium (Non Darcy-flow). The results of optimization are compared with existing data in literature. Also it is shown that the results obtained grom Forchheimer-flow porous model agree much better with the experimental results compared with the natural CONVECTION dary model.

Natural CONVECTION flow on a vertical cylinder is considered here when the Prandtl number is large. Little work has been done in this field apart from some experimental studies which are for lower Prandtl numbers. Here. the singular perturbation technique is used to solve this problem. The method adopted is to split the flow into a thin layer close to the surface of the cylinder, surrounded by a much thicker layer where the velocity is reduced to zero. It is shown that at high Prandtl numbers, the velocity boundary layer tends to be somewhat larger due to large kinematic viscosity relative to thermal diffusivity. The motion of the outer layer, however, seems to be caused by the drag force exerted by the inner layer, not due to the buoyancy itself.The basic properties of the flow are evaluated. The heat transfer coefficient is shown to give good prediction for all ranges of Prandtl numbers.

In this work, the rising of a single bubble in a quiescent liquid under microgravity condition was simulated. In addition to general studies of microgravity effects, the initiation of hydrodynamic CONVECTION, solely due to the variations of interface curvature (surface tension force) and thus the generation of shearing forces at the interfaces was also studied. Then, the variation of surface tension due to the temperature gradient (Marangoni CONVECTION), which can initiate the onset of CONVECTION even in the absence of buoyancy, was studied. The related unsteady incompressible full Navier-Stokes equations were solved using a finite difference method with a structured staggered grid. The interface was tracked explicitly by connected marker points via a hybrid front capturing and tracking method. A one field approximation was used where one set of governing equations is only solved in the entire domain and different phases are treated as one fluid with variable physical properties, while the interfacial effects are accounted for by adding appropriate source terms to the governing equations. Also, a Multi-grid technique, in the context of the projection method, improved convergences and computational stiffness. The results show that the bubble moves in a straight path under microgravity condition, compared to the zigzag motion of bubbles in the presence of gravity. Also, in the absence of gravity, the variation of surface tension force due to interface curvature or temperature gradient can still cause the upward motion of the bubble. This phenomenon was explicitly shown in the results of this paper.

In this paper we would like to present a numerical study of the effect of magnetic fields on natural CONVECTION (magneto-CONVECTION) flow of electrically conducting fluid. The 2D square cavity which was studied is subjected to a sinusoidal temperature conditions. The left and the right walls were respectively heated and cooled with a sinusoidal temperature while the top wall was kept thermally insulated. The equations are solved numerically by employing finite element method (MEF) using the software COMSOL Multiphysics. We presented the results in wide range of Hartmann number and Rayleigh number in terms of isotherm contours, velocities fields streamlines,, and in an average and local Nusselt number which varies sinusoidally. Our results are shown to be in good conformity with the available benchmark solutions.