Thermogravitational separation in horizontal annular porous cell

Thermogravitational separation has until now, been used in different heated vertical cells called thermogravitational columns. The cell can be an annular cavity with two isothermal faces maintained at different temperatures. The main objective of this paper is to study the two dimensional coupled convection with thermodiffusion process. It concerns a theoretical and numerical investigation of species separation in a binary liquid mixture saturating a horizontal porous annulus space where the inner cylinder is heated isothermally. This kind of geometry is used instead of the annular vertical cell, hence the novelty of this technique. Analytical resolution is performed using the perturbation method function of time versus the corresponding physics (Raleigh and Lewis numbers...). Results reveal that the separation can be increased with an optimum for small values of Rayleigh number. Further, these values are less important than the critical value of Raleigh leading to the loss of unicellular flow stability found in literature

A numerical study of viscous dissipation effect on non-Newtonian fluid flow inside elliptical duct

Laminar heat transfer inside duct with elliptical cross section, subjected to uniform wall temperature is studied by taking into account the viscous dissipation. The temperatures distributions are evaluated numerically by using a dynamic Alternating Direction Implicit method (dADI). Nusselt number (Nu) is presented graphically for various Brinkman number (Br) and aspect ratio for a non-Newtonian fluid described by the power law model. The results obtained showed a good agreement with those found in the literature for fluid flow in circular cross section ducts and in elliptical cross section without viscous dissipation effects. It is shown that in the fully developed region and for Br – 0, Nusselt number has a fixed asymptotic value independent of Brinkman number (Br). In the thermally developing region, it is observed a single fixed point independent of heating or cooling condition which the numerical value is equal to the asymptotic Nusselt number. Another relevant feature is that in the fully developed region, the Nusselt number increases with the aspect rati

Application of variational formulation to the periodic conjugated laminar forced convection within ducts

A theoretical study of laminar forced convection with a parabolic velocity profile inside parallel-plate channels and circular ducts, subjected to a sinusoidally varying inlet temperature, is presented. Thermal diffusion in the duct wall and a boundary condition that accounts for external convection are considered. A new methodology is presented to this extended Graetz problem by using the Laplace transform with a Ritz method. The variation of the amplitudes and phase lag for the centerline, wall, and fluid bulk temperature are investigated. The wall heat flux along the channel is also determined. It is concluded that for large values of wall thermal capacitance, the thermal wave is rapidly damped along the duct and the Biot number will slightly affect the dimensionless temperature amplitude. The effects of the wall transverse conduction are more pronounced at large values of the parameter β. The results are plotted and tabulated for comparison with the literatur

APPLICATION OF VARIATIONAL FORMULATION TO THE PERIODIC CONJUGATED LAMINAR FORCED CONVECTION WITHIN DUCTS

A theoretical study of laminar forced convection with a parabolic velocity profile inside parallel-plate channels and circular ducts, subjected to a sinusoidally varying inlet temperature, is presented. Thermal diffusion in the duct wall and a boundary condition that accounts for external convection are considered. A new methodology is presented to this extended Graetz problem by using the Laplace transform with a Ritz method. The variation of the amplitudes and phase lag for the centerline, wall, and fluid bulk temperature are investigated. The wall heat flux along the channel is also determined. It is concluded that for large values of wall thermal capacitance, the thermal wave is rapidly damped along the duct and the Biot number will slightly affect the dimensionless temperature amplitude. The effects of the wall transverse conduction are more pronounced at large values of the parameter β. The results are plotted and tabulated for comparison with the literatur

Coupled radiation and natural convection within an inclined sinusoidal solar collector heated from below

The main objective of this article is to study the effect of coupled mode free convection with surface radiation on the fluid flow behavior inside a tilted solar collector having a flat glass cover and a wavy bottom absorber. The cavity is subject to vertical gradient temperature while its top sidewalls remain thermally insulated. The dimensionless governing equations under Boussinesq approximation are coupled with a radiative model through the boundary conditions and solved by the Finite Volume Method. The numerical results are discussed in terms of streamlines, isotherms, convective and radiative Nusselt number along the cover plate for various aspect ratios, inclination angle, emissivity and Rayleigh number. These results highlighted the condition of the enclosure performance and revealed that the heat and fluid flow fields are affected by surface radiation and the above parameters. In the end, correlations for predicating the convection heat loss in term of averaged Nusselt numbers are developed in both pure free convection and coupled convection-surface radiation modes

Effects of thermal boundary conditions, surface radiation and aspect ratio on thermal performance in “T” shallow cavity

The main objective of this article is to study the effect of 2D coupled mode free convection with surface radiation on the fluid flow behavior in an air filled partitioned and shallow cavity subjected to isothermal or insulated boundary conditions. The dimensionless governing equations under Boussinesq approximation are coupled with a radiative model through the boundaries conditions and solved by the finite volume method. The numerical results are discussed in terms of streamlines, isotherms, convective and radiative Nusselt numbers along the cover plate for various aspect ratios (a, b and c), emissivities and Rayleigh number. These results highlighted the condition of the enclosure performance and revealed among other that isothermal boundaries induce better convective heat exchange compared to adiabatic cases. Also, it is noticed that varying aspect ratio (a) causes strong influence on both Nusselt numbers compared to the aspect ratios (b) and (c). The increase of (ϵo) raises Nuconv and decreases Nurad slightly. Whereas, an increase of (ϵC) leads to minor changes in Nurad when (b) or (c) vary, this effect becomes appreciable with increasing (a)

Flow patterns of non-Newtonian nanofluid flow in cylindrical enclosure with rotating endwall: Effects of nanoparticles concentration

In this paper, a numerical study on the flow structure of non-Newtonian nanofluid in cylindrical enclosure with rotating end wall. The considered nanofluid, MWCNT-water, exhibits a strong power-law shear-thinning behavior with the increase in nanoparticles loading. The main focus in this study is the effect of nanoparticles concentration on the vortex breakdown phenomenon. The simulation results showed that adding a small amount of nanoparticle eliminate the vortex breakdown which is considered as a positive in mixing process. However, the increase in nanoparticles concentration as well as the enclosure aspect ratio promotes the apparition of secondary recirculation zone and stagnation zone