Study Of Natural Convection Flow Research Articles

Numerical Study of Natural Convection Flow in Rectangular Cavity with Viscous Dissipation and Internal Heat Generation for Different Aspect Ratios

Numerical simulations have been performed to investigate the influence of constant volumetric heat generation and viscous dissipation on the unsteady natural convection flow of an incompressible Newtonian fluid contained in a rectangular cavity. The left vertical wall of the cavity is cooled, while the right vertical wall is heated, and the bottom and top walls are adiabatic. A numerical technique based on the implicit finite difference method (IFDM), along with an upwind finite difference scheme and an iterative successive over relaxation (SOR) technique, is employed to solve the governing equations numerically. The effect of physical parameters, namely the modified Rayleigh number (103≤Ra≤107), aspect ratio (1≤A≤4), Prandtl number (Pr=0.7, 1.0, 6.2, 15), volumetric internal heat generation parameter (Qλ=0, 1), and Eckert number (0≤Ec≤10−6), on the streamlines and isotherms are discussed graphically. Variations of maximum stream function, as well as average and local Nusselt number, are also discussed. The results show that the increase in Eckert number from 0 to 10−4 causes the average heat transfer to decrease, while Pr=0.71, Ra=104, and Qλ=0. Additionally, the average heat transfer decreases as the cavity width increases from 1 to 4, while Pr=0.71, Ra = 5×104, Ec=10−6 and Qλ=1. The results of the numerical model used here are in excellent accord with earlier findings.

Numerical Study of Natural Convection Flow in a Square Porous Enclosure Filled with Casson Viscoelastic Fluid

The present simulation, a numerical investigation of natural convection of Casson viscoelastic fluid in a porous square enclosure has been reported. Darcy-Boussinesq approximation mathematical model has been considered. The enclosure has been uniformly heated from the left wall and uniformly cooled from right side wall. The developed partial differential equations of the present computational domain are employed by using stream function approach along with finite difference scheme. The house-computational numerical algorithm has been validated against with the previous work and the computational results have been registered a good correlation. All the important results as shown by streamlines, isotherms, and local Nusselt numbers, the impact of Casson fluid parameter (β), Rayleigh number (Ra) is examined. It has been observed that with the increase in Casson fluid parameter (β), the buoyancy induced fluid circulation and convection effect decreases inside the enclosure. For each Rayleigh number, there correspond a critical Casson fluid parameter (β), for which the heat transfer inside the enclosure takes place solely by conduction mode. It has been also observed that at high Casson viscoelastic fluid the effect of increase in Rayleigh number on average Nusselt number is lesser compared to the effect of increasing Rayleigh number at low Casson viscoelastic fluid.

Approximate Analytical Study of Natural Convection Flow of Non-newtonian Fluid Through Parallel-Pates With Heat Generation

In this present paper, approximate analytical study of natural convection flow of non-Newtonian fluid through Parallel-plates with heat generation is considered. The coupled non-linear momentum and energy equations was solved using perturbation technique. The cases of constant viscosity and temperaturedependent viscosity are treated with the case of temperature-dependent viscosity considered in two models: Reynold's model and Vogel's model. Within the constant viscosity case, results show that increase in the non-Newtonian parametersß, M, decreases the velocity of the fluid flow and increase in these parameters enhances the temperature of the plates. The effects of non-Newtonian and viscosity indices of both Reynold's and Vogel's models on velocity and temperature profiles are presented.

Numerical Simulation and Experimental Study of Natural Convection Flow in a Test Bench for Solar Air Heaters

This paper is intended to check the thermal convection flow during a new solar air heater (SAH) test bench, which is conducted in the LASEM laboratory. In fact, the applied system includes two-passage heater solar air separated by an absorber. On the other hand, a glass piece is connected to the box prototype via a pipe. Then, the piece of the glass is attached to the front side of this device in which an absorber is inserted. Moreover, two circular holes are made on the same face of the box prototype. The first is an entry hole through which hot air goes inside, and an exit hole through which air is released into the surrounding area. The study was conducted using the Navier-Stokes equations associated with the k–ω turbulence model through the use of the newly released Ansys 17.0 software to characterize the aero-thermal structure of our new system operating in natural convection. In these conditions, it has been observed that the hot zone created on the mirror side receiving the solar radiation generates an ascendant movement. It goes from the bottom to the top and enters the box prototype. The same phenomenon is also created in the box where the airflow coming from the solar heat escapes into the environment. This movement created between the hot zone of the solar heat and the box prototype is also imposed in the cold zone of the solar heat on the heat-insulating side. In these conditions, the air movement is however from the top to the bottom. Indeed, the acceleration of the air velocity at the inlet of the solar heat is due to the change of the section which is more reduced by comparison to the rest of the air circulation duct. Based on our experimental results generated in a two-passage solar air heater connected to the box prototype, the computational approach and the simulation results were validated. By referring to the classic solar air heater with one passage, the energy efficiency measured in the same conditions was enhanced and presented the efficient one with an improvement of about 27%. Finally, the numerical results are compared to our experimental results and those obtained by the authors. The comparison proved a good agreement.

A Comparative Study of Natural Convection Flow of Fractional Maxwell Fluid with Uniform Heat Flux and Radiation

This paper focuses on the comparative study of natural convection flow of fractional Maxwell fluid having uniform heat flux and radiation. The well-known Maxwell fluid equation with an integer-order derivative has been extended to a non-integer-order derivative, i.e., fractional derivative. The explicit expression for the temperature and velocity is acquired by utilizing the Laplace transform (LT) technique. The two fractional derivative concepts are used (Caputo and Caputo–Fabrizio derivatives) in the formulation of the problem. Utilizing the Mathcad programming, the effect of certain embedded factors and fractional parameters on temperature and velocity profile is graphically presented.

A Simple Nonlinear Eddy Viscosity Model for Geophysical Turbulent Flows

Eddy viscosity models in turbulence modeling can be mainly classified as linear and nonlinear models. Linear formulations are simple and require less computational resources but have the disadvantage that, those can’t predict actual flow pattern in complex geophysical flows where streamline curvature and swirling motion are predominant. A constitutive equation of Reynolds stress anisotropy is adopted for the formulation of eddy viscosity including all the possible higher order terms quadratic in the mean velocity gradients and a simplified model is developed for actual oceanic flows where only the vertical velocity gradients are important. The simplified formulation is used for the study of natural convection flow in a vertical water column and the results are compared with the observational data and predictions of other existing turbulence models. The developed formulation can be incorporated in other computational fluid dynamics codes for the flow analysis in various engineering applications. The model predictions of marine turbulence and other related data (e.g. sea surface temperature, surface heat flux and vertical temperature profile) can be utilized in determining the effective siting for the Ocean Thermal Energy Conversion (OTEC) plants and in particular for the development of tidal energy projects.

English

English

A mathematical study of natural convection flow through a channel with non-singular kernels: An application to transport phenomena

In this manuscript, we have obtained closed form solution using Laplace transform, inversion algorithm and convolution theorem. The study of mass transfer flow of an incompressible fluid is carried out near vertical channel. Recently, new classes of differential operators have been introduced and recognized to be efficient in capturing processes following the decay law and the crossover behaviors. For the study of heat and mass transfer, we applied the newly differential operators say Atangana-Baleanu (ABC) and Caputo-Fabrizio (CF) to model such flow. This model for temperature, concentration and velocity gradient is presented in dimensionless form. The obtained solutions have been plotted for various values physical parameters like α,Df,Gm,Gr,Sc and Pr on temperature and velocity profile. Our results suggest that for the variation of time the velocity behavior for CF and ABC are reversible. Finally, an incremental value of prandtl number is observed for decrease in the velocity field which reflects the control of thickness of momentum and enlargement of thermal conductivity. Further, dynamical analysis of fluid with memory effect are efficient for ABC as compared to CF.

Numerical Study of Natural Convection Flow of Nanofluid Past a Circular Cone with Cattaneo–Christov Heat and Mass Flux Models

The objective of this study is to analyze the natural convection flow of nanofluid along a circular cone placed in a vertical direction. The generalized heat flux and mass flux models are commonly known as the Cattaneo–Christov heat flux model and mass flux models. In the present study, these models are used for both heat and mass transfers analysis in nanofluid flow. For the governing equations, the Buongiorno transport model is used in which two important slip mechanism, namely thermophoresis and Brownian motion parameters, are discussed. The resulting governing equations in the form of partial differential equations (PDEs) are converted into ordinary differential equations (ODEs) due to similar flow along the surface of a circular cone. To solve these ODEs, a numerical algorithm based on implicit finite difference scheme is utilized. The effects of dimensionless parameters on heat and mass transfer in nanofluid flow are discussed graphically in the form of velocity profile, temperature profile, Sherwood number and Nusselt number. It is noted that in the presence of the Cattaneo–Christov heat flux model and mass flux model, the heat transfer rate decreases by increasing both thermal and concentration relaxation parameters; however, Sherwood number decreases by increasing the thermal relaxation parameter, and increases by increasing the concentration relaxation parameter.

Numerical Investigation of Natural Convection Flow in a Hexagonal Enclosure Having Vertical Fin

Numerical study of natural convection flow in a hexagonal enclosure with a single vertical fin attached to its heated bottom wall has been carried out. Finite element method based Galerkin weighted residual technique is used to solve the governing equation. The horizontal walls of the enclosure are kept at constant high temperature while the inclined walls are kept at constant cold temperature. A vertical heated fin is attached to the hot bottom wall with a length at a position from the left surface having thickness . The Prandlt number for the flow inside the enclosure is 0.71. The results of the problem are presented in graphical and tabular forms and discussed. The fin efficiency and temperature distribution were examined. The numerical results indicate the strong influence of the mentioned parameters on the flow structure and heat transfer as well as temperature. A set of graphical results are presented in terms of streamlines, isotherms contour, temperature profiles, velocity profiles, local Nusselt number and average Nusselt number. The obtained results indicated that the heat transfer rate increases with the increase of Rayleigh number in a hexagonal enclosure. The results are validated comparing with the published works.

Numerical study of the effects of natural convection in a thermoacoustic configuration

This study focuses on natural convection flows within a cylindrical guide containing a porous medium. This configuration is applicable to standing-wave thermoacoustic engines, usually composed of an acoustic resonator where a (short) stack (or porous medium) is inserted, with a heat exchanger placed at one of its ends. The resulting horizontal temperature gradient, when high enough, triggers the onset of an acoustic wave. Natural convection effects are usually neglected in thermoacoustics so that axisymmetry is often assumed. Here a 3D numerical study of natural convection flow is performed using a finite volume code for solving mixed Navier-Stokes and Darcy-Brinkman equations under Boussinesq approximation. The influence of the porous medium’s physical characteristics (permeability, thermal conductivity, anisotropy) on the flow and temperature fields is investigated. It is shown that such flows are fully three-dimensional and therefore can modify significantly starting as well as steady operating conditions of the thermoacoustic engine.

Simultaneous measurement of velocity and temperature fields during natural convection in a water-filled cubical cavity

Many advanced schlieren systems have been reported in the literatures and a great number of it are associated in gas flow study, commonly air. Present research proposes an efficient use of Z-type schlieren technique for simultaneous measurement of ray-averaged velocity as well as temperature fields beside qualitative flow visualization. Experiments are conducted to study natural convective flow in de-ionized water in a differentially heated cubical enclosure. The same set of transient schlieren images has been used for simultaneous measurement of velocity and temperature field. The velocity field is also determined by using laser based particle image velocimetry (PIV) to compare with schlieren based technique. The developed schlieren system has been used to obtain ray-averaged quantities, such as, thermal and hydrodynamic boundary layer thicknesses, temperature gradient and temperature fields, distribution of local Nusselt number along the thermally active walls, average Nusselt number and velocity field. In this work, the above quantities have been simultaneously determined for the first time using halogen projector lamp based Z-type calibration schlieren system. The results inspire the use of calibration schlieren system for the study of natural convective flow in water-filled cubical enclosures. The above results also provide experimental data as new benchmark for researchers to compare results for high Rayleigh number free convective flow with water as the working medium.

Natural convective flow of a magneto-micropolar fluid along a vertical plate

This paper presents a numerical study of natural convective flow of an electrically conducting viscous micropolar fluid past a vertical plate. Internal heat generation (IHG) versus without IHG in the medium are discussed in the context of corresponding similarity solutions. Results are presented in terms of velocity, angular velocity, temperature, skin friction in tabular forms, local wall-coupled stress, and Nusselt number. Computations have been accomplished by parametrizing the micropolar, micro-rotation, magnetic field, suction parameters, and the Prandtl number. Several critical issues are addressed at the end of the paper with reference to a previous study by El-Hakiem. The study is relevant to high-temperature electromagnetic materials fabrication systems.

Numerical analysis of convective flow and thermal stratification in a cryogenic storage tank

ABSTRACTIn this study, the liquid–vapor mixture model was used for a numerical study of natural convective flow in a cryogenic tank with a capacity of 4.9 m3 under various conditions of heat flux and filling level to understand the early stages of convective flow phenomena and the consequent thermal stratification of cryogenic liquid. Two cryogens—liquefied natural gas (LNG) and liquefied nitrogen (LN2)—were compared to observe their effects. LN2 exhibited faster vaporization owing to its lower heat of vaporization. It was observed that higher heat flux and lower filling level led to faster vaporization and relatively vigorous heat transfer, showing early thermal stratification.

Natural convection in a horizontal cylindrical annulus filled with a porous medium saturated by a nanofluid using Tiwari and Das’ nanofluid model

This paper deals with a numerical study of natural convection flow and heat transfer inside a concentric horizontal annulus filled with a porous medium saturated by a cuprum (Cu)-water nanofluid. The inner and outer cylinders are kept at different constant temperatures. First, the governing partial differential equations in dimensional formulation in a polar coordinate system for the physical domain are transformed in dimensionless form in terms of stream function-temperature formulation. These equations along with the corresponding boundary conditions were solved numerically by the finite difference method. Particular efforts have been focused on the effects of the Rayleigh number, porosity of the porous medium, solid volume fraction parameter of nanoparticles, annulus radius ratio, and the solid matrix of the porous medium (glass balls and aluminum foam) on the local and average Nusselt numbers, streamlines and isotherms. It is found that a very good agreement exists between the present results and those from the open literature.

Numerical Study of Natural Convection Flow in a Square Cavity with Linearly Heating on Bottom Wall Using Copper-Water Nanofluid

Numerical Study of Natural Convection Flow in a Square Cavity with Linearly Heating on Bottom Wall Using Copper-Water Nanofluid

Natural convection flow of viscous fluid over triangular wavy horizontal surface

The purpose of this paper is to conduct a numerical study of natural convection flow along an irregular semi-infinite triangular wavy horizontal surface. Coordinate transformation is introduced to transform the boundary layer equations into a form which is more suitable for numerical integration. Implicit finite difference iterative numerical scheme is employed to produce solutions of the problem. Effect of wave amplitude is studied in detail. Important features of the flow field are discussed graphically in terms of skin friction, heat transfer rate, streamlines and isotherms. Although amplitude of the wavy surface play its role in enhancement in the heat transfer rate but it is found difficult to accomplish numerical computations for a>1.5. Thus, it is concluded that heat liberation is more effective in sinusoidal wavy surface than in triangular surface.

An analysis on free convection flow, heat transfer and entropy generation in an odd-shaped cavity filled with nanofluid

A study of natural convective flow, heat transfer and entropy generation in an odd-shaped geometry is presented here. The geometry considered is a combination of the horizontal and vertical enclosure shapes. The cavity is filled with Cu–water nanofluid. The numerical study focuses specifically on the effect of natural convection parameter and solid volume fraction of nanoparticle on the average Nusselt number, total entropy generation and Bejan number. Also isotherms, stream function and entropy generation due to heat transfer are presented for various Rayleigh number and solid volume fraction. The governing equations are solved by using penalty finite element method with Galerkins weighted residual technique. The results reveal that increasing Rayleigh number causes increase of the average Nusselt number as well as the heat transfer term of entropy generation and decrease of the viscous term. The proper choice of Rayleigh number could be able to maximize heat transfer rate simultaneously minimizing entropy generation.

New analytical method for the study of natural convection flow of a non‐Newtonian fluid

PurposeThe purpose of this paper is to discuss the natural convection flow of an incompressible third grade fluid between two parallel plates. The basic equations governing the flow are reduced to a nonlinear ordinary differential equation.Design/methodology/approachThe resulting nonlinear ordinary differential equation is solved by multi‐step differential transform method (MDTM).FindingsThe obtained solutions in comparison with the numerical solutions (fourth‐order Runge‐Kutta) admit a remarkable accuracy.Originality/valueThe analysis illustrates the validity and the great potential of the MDTM in solving nonlinear differential equations.

Natural convection flow and heat transfer in an eccentric annulus filled by Copper nanofluid

A numerical study of natural convection flow and heat transfer of Copper (Cu)–water nanofluid inside an eccentric horizontal annulus is presented. The inner and outer cylinders are kept at constant temperatures as Th and Tc, respectively. First the governing equations in terms of stream function-vorticity formulation in polar coordinate system for eccentric physical domain are derived and then transformed to a rectangular domain in order to get better accuracy of the solution near the boundaries. The resultant governing equations are discretized with a finite volume technique based on second order upwind scheme and then solved by iteration. The effects of the eccentricity ε, radii ratio (RR), the nanoparticles volume fraction parameter ϕ, the Rayleigh number Ra and the Prandtl number Pr on the mean Nusselt number Nu, streamlines and isotherms are investigated. The results are also discussed in detail. It is found that a very good agreement exist between the present results and those from the open literature.