Papers by Keyword: Free Convection

Abstract: Abstract. The topic of free convection thermal transmission through different geometrical shapes of enclosures is an engaging subject. It has caught the attention of the researchers during the last decades according to its significance in lots of engineering applications. Nuclear reactors, solar collectors, cooling electronic equipment, Oil wells, cooling electric components (as in the copper electric wires that are surrounded by the housing), and many industrial systems. Many parameters are discussed and analyzed to see their effect on the process of transferring heat such as: the effect of the geometrical shape, Nusslet number, and Rayliegh number. The studies were divided into seven categories based on the geometrical shape of the enclosure ( square , triangular, circular, trapezoidal, polygonal, elliptical, and wavy). The governing equations of the free convective thermal transmission were stated. The objective of this study is to collect the data from a large number of previous studies and compare them to reach a conclusion about the best results.

Abstract: We try through this research to present a detailed study on free convection heat transfer inside a closed space. The work is carried out in numerical way, using the method called finite volume. The governing equations are solved for numerical simulations of steady state and laminar regime. The studied domain is an annular space consisting mainly of two cylinders positioned horizontally, the inner cylinder has an elliptical shape with different aspect ratio (E) while the outer one has a single shape which is circular. The primary conditions adopted in this research are as follow: the outer cylinder has a cold surface, while the inner cylinder has a cold surface. The space between cylinders is considered to be filled with fluid of different values of thermo-physical proprieties (Pr). The fluid in the space moves under the influence of thermal buoyancy which is controlled by Ri number. The pertinent parameters for this research are: the aspect ratio of elliptical cylinder which is E = 0.1 to 1, the Prandtl number Pr = 1 to 100 and finally the Richardson number Ri = 10³, 10⁴ and 10⁵. The results of this work show that the elliptical form allows an increase in thermal transfer activity. Also, values of the number Pr have a limited effect on heat transfer.

Abstract: The effect of viscous dissipation on heat transfer through nano-fluid in a vertical wavy channel filled with porous media has been studied. The consequential differential equations are simplified by the R-K method of 6th order. The numerical obtained results are shown in the graphs. The significant results of fluid flow and heat transfer rate and its properties are shown graphically. Nusslet values are calculated a for varying the governing parameters φ Da, Gr, ε, Ec and the remaining parameters are to be constants.

Abstract: This study extends previous investigation on ohmic heating of magnetohydrodynamic viscous fluid flow over a continuous moving plate to include radiative heat-loss, viscous dissipation and buoyancy effects. The mathematical formulation representing the modified physical model involves a system of three partial differential equations, which are transformed into a system of two coupled non-linear ordinary differential equations using suitable dimensionless variables. Thereafter, the resulting dimensionless system of equations governing modified model are solved via Homotopy Analysis Method (HAM). The accuracy and convergence of solutions are vali￾dated by comparing the results obtained with those in literature and they are in good agreement. Parametric study is performed to illustrate the effects of emerging parameters on fluid velocity and temperature, skin friction coefficient and Nusselt number. It is found that the impacts of pertinent parameters due to the extensions are significant and these are presented in graphs and tables. The results indicate that the skin friction coefficient and the heat transfer rate increase with the increasing values of thermal radiation and decrease with the increasing value of viscous dissipation parameter.

Abstract: The main trends and prospects of water resources consumption, as well as existing ways of obtaining fresh drinking water, were analyzed. The design of a vortex condenser of atmospheric moisture has been provided. Its operating principle is based on the organization of free-convective flow under the temperature drop effect and air-cooling to a temperature below the dew point. The designed vortex condenser of atmospheric moisture runs on solar energy and do not require using additional energy sources. The results of numerical simulation of the flow structure in a vortex condenser of atmospheric moisture and experimental data, which confirms the formation of air flow inside the condenser and moisture condensation in its lower part, are presented.

Abstract: The coupled of free convection with surface radiation in an annular region of two concentric vertical cylinders filled with air has been numerically investigated. The steady-state continuity, Navier–Stokes and energy equations were carried out by the finite volume method, and the Discrete Ordinates Method (DOM) was used to solve the radiative heat transfer equation (RTE). The computations have been performed for 10³ ≤Ra≤ 10⁶, with the emissivity coefficient of all the walls varying between 0 and 1. The influence of the both, Rayleigh numbers and emissivity coefficient of the wall for fixed height ratio X=0.5 on natural convection and radiation heat transfer in enclosure have been solved. The result shows that surface radiation significantly altered the temperature distribution and the flow patterns, especially at higher Rayleigh numbers. The average Nusselt number has also been discussed for different emissivity through the enclosure.

Abstract: The investigation is undertaken to study the thermal diffusion and radiation effects on unsteady MHD heat and mass transfer flow past a semi-infinite inclined porous plate embedded in a porous medium in a slip flow regime with variable suction in the presence of first order chemically reaction. The analytical solutions for velocity, temperature and concentration fields are obtained by reducing the governing nonlinear coupled partial differential equations in dimensionless form into a system of ordinary differential equations, using perturbation method. The effect of pertinent flow parameters on velocity, temperature, concentration, the skin friction, the rate of heat transfer and the rate of mass transfer are studied graphically.

Abstract: The objective of investigation is to study the hydro-magnetic boundary layer micropolar nanofluid steady flow past a stretching sheet with a non-uniform heat suction/sink by taking into account of nanofluids containing Cu– water, TiO₂–water, Al₂O₃–water, and Ag–water. As per the geometry of the flow configuration the conservation laws are transformed into a non-linear model. Using the appropriate analoguestransformations, the resultant equations are employing order approach along with shooting technique to derive closed form solutions for momentum, angular velocity, and temperature fields as well as couple stress, skin friction, local Nusselt number, and then to analyse and physical insight of various flow parameters on these fields. Also the numerical computations are performed and plotted through graphs and tables. It is found that the effect of volume fraction of nanoparticles on the fluid velocity, it decreases due to the absence of surface tension forces and hence, the momentum boundary layer thickness reduced. Furthermore, comparisons with published results are in very good agreement. Nomenclature

Abstract: In this article, a comparative analysis of free convective Blasius and Sakiadis flows of a viscous fluid over a vertical porous surface is presented. The relationship between the flow rate and pressure drop as the Newtonian fluid flows past a porous medium is linear; hence Darcy model is adopted. Suitable similarity variables are employed to transform the governing non-linear partial differential equations into a set of coupled non-linear ordinary differential equations. An approximate analytical solution of the coupled ordinary differential equation is obtained using Optimal Homotopy Analysis method (OHAM). The computational results for velocity and temperature profiles are shown graphically for various flow parameters and analyzed. The results show that an increase in convective parameter leads to increase in velocity and temperature profiles. Also, increasing buoyancy parameter increases the velocity profile and decreases the temperature profiles for both Sakiadis and Blasius flow. The temperature distribution at the maximum value of Prandtl in Sakiadis case is greater than the temperature distribution at the maximum value of Prandtl even in Blasius case.

Abstract: Free convection on a vertical surface with Newtonian heating of the form proposed by Merkin (1994) in the fluid-filled porous medium is considered on the basis of the full equations of a viscous liquid. Using dimensional analysis a set of criteria that define the characteristics of flow and heat transfer was derived. Asymptotic analysis of the full equations allowed us to determine the region of applicability of the boundary layer approximation, which was used in the previous studies of this problem. Darcy parameter influence was studied; the composite numerical and analytical solution for stream function and temperature was derived.