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Showing papers on "Combined forced and natural convection published in 2007"


Journal ArticleDOI
TL;DR: In this article, the authors investigated the behavior of nanofluids inside a two-sided lid-driven differentially heated square cavity to gain insight into convective recirculation and flow processes induced by a nano-fluid.

1,797 citations


Journal ArticleDOI
TL;DR: In this paper, a two phase mixture model has been implemented for the first time to study a turbulent forced convection heat transfer in a circular tube with a nanofluid consisting of water and 1 vol.% Cu.

396 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of the buoyancy force, the centrifugal force and the nanoparticles volume fraction on the secondary flow, axial velocity and the skin friction coefficient were investigated.

261 citations


Journal ArticleDOI
TL;DR: In this article, the effects of inclination of the cavity on the flow and thermal fields are investigated for inclination angles ranging from 0° to 30°, and the average Nusselt number is found to increase with cavity inclination.

244 citations


Journal ArticleDOI
TL;DR: In this article, a numerical investigation of unsteady laminar mixed convection heat transfer in a lid driven cavity is executed, where the forced convective flow inside the cavity is attained by a mechanically induced sliding lid, which is set to oscillate horizontally in a sinusoidal fashion.
Abstract: A numerical investigation of unsteady laminar mixed convection heat transfer in a lid driven cavity is executed. The forced convective flow inside the cavity is attained by a mechanically induced sliding lid, which is set to oscillate horizontally in a sinusoidal fashion. The natural convection effect is sustained by subjecting the bottom wall to a higher temperature than its top counterpart. In addition, the two vertical walls of the enclosure are kept insulated. Discretization of the governing equations is achieved through a finite element scheme based on the Galerkin method of weighted residuals. Comparisons with previously reported investigations are performed and the results show excellent agreement. Temporal variations of streamlines, isotherms, and dimensionless drag force, and Nusselt number are presented in this investigation for various pertinent dimensionless groups. Fluid flow and heat transfer characteristics are examined in the domain of the Reynolds number, Grashof number and the dimensionless lid oscillation frequency such that: 10 2 ⩽ Re ⩽ 10 3 , 10 2 ⩽ Gr ⩽ 10 5 and 0.1 ⩽ ϖ ⩽ 5 . The working fluid is assigned a Prandtl number of 0.71 throughout this investigation. The obtained results reveal that the Reynolds number and Grashof number would either enhance or retard the energy transport process and drag force behavior depending on the conduct of the velocity cycle. Moreover, relatively small lid oscillation values are found to constrain the lid associated motion to a shallow depth from the sliding lid plane.

147 citations


Journal ArticleDOI
TL;DR: In this paper, the stagnation point flow toward a stretching vertical sheet is investigated and the features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed.
Abstract: The stagnation point flow toward a stretching vertical sheet is investigated in this study. The temperature and velocity of the sheet as well as the velocity of the external flow are assumed to vary in a power law with the distance from the stagnation point. The governing system of equations is first transformed into a dimensionless form, and then the resulting equations are solved numerically by a finite-difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. It is found that, for opposing flow, dual solutions exist in the neighborhood of the separation region, whereas for assisting flow the solution is unique.

138 citations


Book ChapterDOI
01 Jan 2007
TL;DR: In this paper, the Earth's liquid outer core is stirred by thermal and compositional convection, and the issues of how fast the convective motions are, what is their morphology, and how this relates to the heat transport are discussed.
Abstract: The Earth’s liquid outer core is stirred by thermal and compositional convection. In thermal convection the buoyancy is due to temperature fluctuations, while in compositional convection it is produced by light material released at the inner-core boundary. Convection in the core is strongly supercritical, and is greatly affected by rotation and magnetic field. In this review, we focus on the issues of how fast the convective motions are, what is their morphology, and how this relates to the heat transport. Core convection is believed to be a primary source of dynamo action, and so it is responsible for the Earth’s magnetic field. We therefore also consider how the morphology of core convection affects the magnetic field generated.

129 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated steady mixed convection in a square lid-driven cavity under the combined buoyancy effects of thermal and mass diffusion and solved the transport equations numerically using the Galerkin weighted residual method.

119 citations


Journal ArticleDOI
TL;DR: In this article, the effect of chemical reaction and variable viscosity on hydromagnetic mixed convection heat and mass transfer for Hiemenz flow through porous media has been studied in the presence of radiation and magnetic field.

115 citations


Journal ArticleDOI
TL;DR: The measured profiles of plume numbers and of vertical vorticity quantify the morphological transition of sheetlike plumes to mushroomlike ones and the mixing and merging or clustering of mushroomlike plume.
Abstract: An experimental study of the morphological evolution of thermal plumes in turbulent thermal convection is presented. Individual sheetlike plumes are extracted and their area, circumference, and "heat content" are found to all exhibit log-normal distributions. As the sheetlike plumes move across the plate they collide and convolute into spiraling swirls. These swirls then spiral away from the plates to become mushroomlike plumes which are accompanied by strong vertical vorticity. The measured profiles of plume numbers and of vertical vorticity quantify the morphological transition of sheetlike plumes to mushroomlike ones and the mixing and merging or clustering of mushroomlike plumes. The fluctuating vorticity is found to have the same exponential distribution and scaling behavior as the fluctuating temperature.

104 citations


Journal ArticleDOI
TL;DR: In this article, the effect of Marangoni convection on the flow and heat transfer within a power-law liquid film on an unsteady stretching sheet is examined, and the governing equations are non-dimensionalized using suitable transformation variables and the resulting transformed PDEs are then solved numerically by an implicit finite-difference scheme.

Journal ArticleDOI
TL;DR: The motion of the sensor particle exhibits dynamics close to that of Lagrangian tracers in hydrodynamic turbulence, and statistics of temperature, velocity, and heat transport in turbulent thermal convection are reported on.
Abstract: We have developed a small, neutrally buoyant, wireless temperature sensor. Using a camera for optical tracking, we obtain simultaneous measurements of position and temperature of the sensor as it is carried along by the flow in Rayleigh-Benard convection, at Ra approximately 10;{10}. We report on statistics of temperature, velocity, and heat transport in turbulent thermal convection. The motion of the sensor particle exhibits dynamics close to that of Lagrangian tracers in hydrodynamic turbulence. We also quantify heat transport in plumes, revealing self-similarity and extreme variations from plume to plume.

Journal ArticleDOI
TL;DR: In this paper, the behavior of an air breathing fuel cell (ABFC) operated on dry-hydrogen in dead-ended mode is studied using theoretical analysis, and a one-dimensional, non-isothermal, combined heat and mass transport model is developed that captures the coupling between water generation, oxygen consumption, self-heating and natural convection at the air breathing cathode.

Journal ArticleDOI
TL;DR: In this paper, a critical review is made of recent studies of the modeling of viscous dissipation in a saturated porous medium, with applications to either forced convection or natural convection.
Abstract: A critical review is made of recent studies of the modeling of viscous dissipation in a saturated porous medium, with applications to either forced convection or natural convection. Alternative forms of the viscous dissipation function are discussed. Limitations to the concept of fully developed convection are noted. Special attention is focused on the roles of viscous dissipation and work done by pressure forces (flow work) in natural convection in a two-dimensional box with either lateral or bottom heating.

Journal ArticleDOI
TL;DR: In this article, an analytical closed-form solution of the unsteady hydro-magnetic natural convection heat and mass transfer flow of a rotating, incompressible, viscous Boussinesq fluid is presented in the presence of radiative heat transfer and a first order chemical reaction between the fluid and the diffusing species.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the hydrogeologic parameters governing density effects in a mixed convection system during the injection, storage and recovery of a freshwater bubble in a saline (isotropic and homogeneous) aquifer.

Journal ArticleDOI
TL;DR: In this article, the effect of thermal radiation on a steady two-dimensional mixed convection laminar flow of viscous incompressible optically thick fluid along a vertical wavy surface has been investigated.

01 Jan 2007
TL;DR: In this paper, the authors studied the MHD flow past an infinite vertical oscillating plate through a porous medium, taking account of the presence of free convection and mass transfer.
Abstract: The objective of this paper is to study the MHD flow past an infinite vertical oscillating plate through porous medium, taking account of the presence of free convection and mass transfer. The governing equations are solved in closed form by Laplace-transform technique. The results are obtained for velocity, temperature, concentration, Nusselt number and skin-friction. The effects of various material parameters are discussed on flow variables and presented by graphs.

Journal ArticleDOI
TL;DR: In this paper, the steady mixed convection boundary layer flow over a vertical impermeable surface embedded in a porous medium was studied, where the viscosity of the fluid varies inversely as a linear function of the temperature.

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional, steady, mixed convection flow in an enclosure filled with a Darcian fluid-saturated uniform porous medium is considered and the governing equations are normalized and solved numerically with boundary conditions by finite volume approach using third order accurate upwinding scheme.
Abstract: Two-dimensional, steady, mixed convection flow in an enclosure filled with a Darcian fluid-saturated uniform porous medium is considered. Both the left wall and the right wall are moving upwards with same velocity. They are maintained at cold and hot constant temperatures respectively. The top and the bottom walls are fixed and are thermally insulated. The governing equations are normalized and solved numerically with boundary conditions by finite volume approach using third order accurate upwinding scheme (deferred QUICK). To validate the code, comparisons are made with previously published work and are found to be in excellent agreement. The study is conducted by varying the key parameters i.e., Richardson number (Ri = Gr/Re 2), Darcy number (Da = κ/H 2) and Grashof number (Gr = g β H 3ΔT/ν 2) and fixing Prandtl number (Pr = 0.71). A parametric study is conducted and a set of streamline and isotherm plots are presented. The average Nusselt number reaches a value of 1 asymptotically when the Ri is gradua...

Journal ArticleDOI
TL;DR: In this article, the effect of thermal radiation with mixed convection for a gray fluid in rectangular horizontal ducts has been numerically examined in detail, focusing on the effects of thermal buoyancy and radiative transfer on the development of temperature, the friction factor and the Nusselt number.

Journal ArticleDOI
TL;DR: In this article, an analysis of forced convection heat transfer in micro-channel heat sinks for electronic system cooling is presented, where the velocity field in the microchannel is first solved by a finite-difference scheme, and then the energy equations governing the solid and fluid phases are solved simultaneously for the temperature distributions.

Journal ArticleDOI
TL;DR: In this article, the melting effect on mixed convective heat transfer from a porous vertical plate with uniform wall temperature in the liquid-saturated porous medium with aiding and opposing external flows is numerically examined at steady state.

Journal ArticleDOI
TL;DR: In this paper, the authors describe heat transfer characteristics of turbulent supercritical carbon dioxide flow in vertical tubes with circular, triangular, and square cross-sections, and propose an improved heat transfer correlation, which can be applicable to both forced convection and mixed convection regimes, and compared with previous ones.

Journal ArticleDOI
TL;DR: In this article, the authors presented a computational study of the forced convection heat transfer around two circular cylinders in tandem, where Axisymmetric, steady, laminar flow around the cylinders was assumed.

Journal ArticleDOI
TL;DR: In this article, the effects of the mixed convection parameter, Gr/Re, the Knudsen number, Kn, and the ratio of wall temperature difference, r T, on the microchannel hydrodynamic and thermal behaviors are determined.
Abstract: In this study, fully developed mixed convective heat transfer of a Newtonian fluid in an open-ended vertical parallel plate microchannel is analytically investigated by taking the velocity slip and the temperature jump at the wall into account. The effects of the mixed convection parameter, Gr/Re, the Knudsen number, Kn, and the ratio of wall temperature difference, r T , on the microchannel hydrodynamic and thermal behaviors are determined. Finally, a Nu=f(Gr/Re,Kn,r T ) expression is developed.

Journal ArticleDOI
TL;DR: In this article, the effects of thermal buoyancy on flow of a viscoelastic second grade fluid past a vertical, continuous stretching sheet of which the velocity and temperature distributions are assumed to vary according to a power-law form.
Abstract: In the present study we have explored the effects of thermal buoyancy on flow of a viscoelastic second grade fluid past a vertical, continuous stretching sheet of which the velocity and temperature distributions are assumed to vary according to a power-law form. The governing differential equations are transformed into dimensionless form using appropriate transformations and then solved numerically. The methods here employed are (1) the perturbation method together with the Shanks transformation, (2) the local non-similarity method with second level of truncation and (3) the implicit finite difference method for values of ξ ( = Gr x /Re 2 , defined as local mixed convection parameter) ranging in [0, 10]. The comparison between the solutions obtained by the aforementioned methods found in excellent agreement. Effects of the elasticity parameter λ on the skin-friction and heat transfer coefficients have been shown graphically for the fluids having the values of the Prandtl number equal to 0.72, 7.03 and 15.0. Effects of the viscoelastic parameter and the mixed convection parameter, ξ, on the temperature and velocity fields have also been studied. We notice that with the increase in visco-elastic parameter λ, velocity decreases whereas temperature increases and that velocity gradient is higher than that of temperature.

Journal ArticleDOI
TL;DR: In this article, heat transfer to the wall of a small pressure vessel during filling with some different kinds of gas was investigated experimentally, where the vessel was orientated vertically with the inlet at the top.
Abstract: Heat transfer to the wall of a small pressure vessel during filling with some different kinds of gas was investigated experimentally. The vessel was orientated vertically with the inlet at the top. The space-averaged Nusselt number for the curved wall was found to be a function of both the Reynolds and Rayleigh numbers indicating a mixed convection heat transfer situation. A correlation is proposed for the heat transfer coefficient during charging of the vessel. For the six positions where measurements were taken, the local heat transfer coefficient typically did not differ from the space-averaged value by more than about 30 percent. Measurements were also taken during discharging to atmospheric pressure. For discharging, some of the data was found to agree with a correlation for natural convection in cylindrical geometry. Local Nusselt numbers for discharging tended to be higher towards the bottom of the vessel.

Journal ArticleDOI
TL;DR: In this article, the authors used the large eddy simulation method together with different subgrid scale models to study the near-wall behavior of the boundary layer and the turbulence structure.
Abstract: The natural convection boundary layer in a tall cavity with an aspect ratio of AR=5 is studied numerically. The Rayleigh number based on the width of the cavity is RaW=4.028×108. The large eddy simulation method together with different subgrid scale models are used to study the near-wall behavior of the boundary layer and the turbulence structure. It is found that the dynamic subgrid scale model is the most accurate model in terms of predicting the transition location. Results also indicate that the conventional grid resolutions expressed in viscous units that are used for forced convection flows are not appropriate in the case of the natural convection flows and higher grid resolutions are necessary. The turbulence statistics are studied in both the turbulent and the transition regions. Although the results of the fully turbulent region show no important grid dependency, it is found that the accuracy of the results in the transition region is highly grid dependent, suggesting that the subgrid scale fluct...

Journal ArticleDOI
TL;DR: Turbulent convection models (TCMs) based on hydrodynamic moment equations are compared with the classical mixing-length theory (MLT) in solar models as discussed by the authors, and it is found that TCMs usually give larger convective heat fluxes than the MLT does, and the heat transport efficiency is sensitively related to the dissipation parameters used in the TCMs.
Abstract: Turbulent convection models (TCMs) based on hydrodynamic moment equations are compared with the classical mixing-length theory (MLT) in solar models. The aim is to test the effects of some physical processes on the structure of the solar convection zone, such as the dissipation, diffusion and anisotropy of turbulence that have been ignored in the MLT. Free parameters introduced by the TCMs are also tested in order to find appropriate values for astrophysical applications. It is found that the TCMs usually give larger convective heat fluxes than the MLT does, and the heat transport efficiency is sensitively related to the dissipation parameters used in the TCMs. As a result of calibrating to the present solar values, our solar models usually have rather smaller values of the mixing length to local pressure scaleheight ratio than the standard solar model. The turbulent diffusion is found to have important effects on the structure of the solar convection zone. It leads to significantly lowered and expanded profiles for the Reynolds correlations, and a larger temperature gradient in the central part of the superadiabatic convection region but a smaller one near the boundaries of the convection zone. It is interesting to note that, due to a careful treatment of turbulence developing towards isotropic state, our non-local TCM results in radially dominated motion in the central part and horizontally dominated motion near the boundaries of the convection zone, just as what has been observed in many 3D numerical simulations. Our solar models with the TCMs give small but meaningful differences in the temperature and sound speed profiles compared with the standard solar model using the MLT.