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Article

Igor V Miroshnichenko and M A Sheremet

The purpose of this paper is to present transient turbulent natural convection with surface thermal radiation in a square differentially heated enclosure using…

Abstract

Purpose

The purpose of this paper is to present transient turbulent natural convection with surface thermal radiation in a square differentially heated enclosure using non-primitive variables like stream function and vorticity.

Design/methodology/approach

The governing equations formulated in dimensionless variables “stream function, vorticity and temperature,” within the Boussinesq approach taking into account the standard two equation k-ε turbulence model with physical boundary conditions have been solved using an iterative implicit finite-difference method.

Findings

It has been found that using of the presented algebraic transformation of the mesh allows to effectively conduct numerical analysis of turbulent natural convection with thermal surface radiation. It has been shown that the average convective Nusselt number increases with the Rayleigh number and decreases with the surface emissivity, while the average radiative Nusselt number is an increasing function of these key parameters. It has been shown that a presence of surface thermal radiation effect leads to an expansion of the eddy viscosity zones close to the walls.

Originality/value

It should be noted that for the first time in this paper we used stream function and vorticity variables with very effective algebraic transformation of the mesh in order to create a non-uniform mesh for an analysis of turbulent flow. Such method allows to reduce the computational time essentially in comparison with using of the primitive variables. The considered method has been successfully validated on the basis of the experimental and numerical data of other authors in case of turbulent natural convection without thermal radiation. The used numerical method would benefit scientists and engineers to become familiar with the analysis of turbulent convective heat and mass transfer, and the way to predict the properties of the turbulent flow in advanced nuclear systems, in industrial sectors including transportation, power generation, chemical sectors, ventilation, air-conditioning, etc.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 25 no. 7
Type: Research Article
ISSN: 0961-5539

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Article

Mahmoud Salari, Mohammad Mehdi Rashidi, Emad Hasani Malekshah and Masoud Hasani Malekshah

Because the local Re numbers, ratio of inertia to viscous forces, are not same at different regions of the enclosures, the present study aims to deal with the influences…

Abstract

Purpose

Because the local Re numbers, ratio of inertia to viscous forces, are not same at different regions of the enclosures, the present study aims to deal with the influences of using the turbulent/transition models on numerical results of the natural convection and flow field within a trapezoidal enclosure.

Design/methodology/approach

The three-dimensional (3D) trapezoidal enclosure with different inclined side walls of 75, 90 and 105 degrees are considered, where the side walls are heated and cooled at Ra = 1.5 × 109 for all cases. The turbulent models of the k-ε-RNG, k- ω-shear-stress transport (SST) and the newly developed transition/turbulent model of Reθ-γ-transition SST are utilized to analyze the fluid flow and heat transfer characteristics within the enclosure and compared their results with validated results.

Findings

Comprehensive comparisons have been carried out for all cases in terms of flow and temperature fields, as well as turbulent quantities, such as turbulent kinetic energy and turbulent viscosity ratio. Furthermore, the velocity and thermal boundary layers have been investigated, and the approximate transition regions for laminar, transitional and turbulent regimes have been determined. Finally, the heat transfer coefficient and skin friction coefficient values have been presented and compared in terms of different turbulent models and configurations. The results show that the transition/turbulence model has better prediction for the flow and heat fields than fully turbulent models, especially for local parameters for all abovementioned governing parameters.

Originality value

The originality of this work is to analyze the 3D turbulent/transitional natural convection with different turbulence/transition models in a trapezoidal enclosure.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 12
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

C.D. Pérez‐Segarra, A. Oliva, M. Costa and F. Escanes

In this paper a numerical simulation, based on finite differencetechniques, has been developed in order to analyse turbulent natural andmixed convection of air in internal…

Abstract

In this paper a numerical simulation, based on finite difference techniques, has been developed in order to analyse turbulent natural and mixed convection of air in internal flows. The study has been restricted to two‐dimensional cavities with the possibility of inlet and outlet ports, and with internal heat sources. Turbulence is modelled by means of two‐equation k‐ε turbulence models, both in the simplest form using wall functions and in the more general form of low‐Reynolds‐number k‐ε models. The couple time average governing equations (continuity, momentum, energy, and turbulence quantities) are solved in a segregated manner using the SIMPLEX method. An implicit control volume formulation of the differential equations has been employed. Some illustrative numerical results are presented to study the influence of geometry and boundary conditions in cavities. A comparison of different k‐ε turbulence models has also been presented.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 5 no. 1
Type: Research Article
ISSN: 0961-5539

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Article

Alireza Rahimi, Ali Dehghan Saee, Abbas Kasaeipoor and Emad Hasani Malekshah

The purpose of this paper is to carry out a comprehensive review of some latest studies devoted to natural convection phenomenon in the enclosures because of its…

Abstract

Purpose

The purpose of this paper is to carry out a comprehensive review of some latest studies devoted to natural convection phenomenon in the enclosures because of its significant industrial applications.

Design/methodology/approach

Geometries of the enclosures have considerable influences on the heat transfer which will be important in energy consumption. The most useful geometries in engineering fields are treated in this literature, and their effects on the fluid flow and heat transfer are presented.

Findings

A great variety of geometries included with different physical and thermal boundary conditions, heat sources and fluid/nanofluid media are analyzed. Moreover, the results of different types of methods including experimental, analytical and numerical are obtained. Different natures of natural convection phenomenon including laminar, steady-state and transient, turbulent are covered. Overall, the present review enhances the insight of researchers into choosing the best geometry for thermal process.

Originality/value

A comprehensive review on the most practical geometries in the industrial application is performed.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Mohamed Omri and Nicolas Galanis

The purpose of this paper is to evaluate the capacity of two equation turbulence models to reproduce mean and fluctuating quantities in the case of both natural convection

Abstract

Purpose

The purpose of this paper is to evaluate the capacity of two equation turbulence models to reproduce mean and fluctuating quantities in the case of both natural convection and isothermal flows.

Design/methodology/approach

Numerical predictions of mean velocity profiles, air and wall temperatures as well as turbulent kinetic energy by three different two equation models (standard kε, renormalisation group kε and shear‐stress transport‐kω) are compared with corresponding experimental values.

Findings

The prediction of mean velocities and temperatures is in all cases satisfactory. On the other hand, the prediction of turbulent quantities is less precise.

Originality/value

The three models under consideration in this paper can be used for engineering applications such as HVAC calculations.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 1
Type: Research Article
ISSN: 0961-5539

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Article

Igor Miroshnichenko, Mikhail Sheremet and Ali J. Chamkha

The purpose of this paper is to conduct a numerical analysis of transient turbulent natural convection combined with surface thermal radiation in a square cavity with a…

Abstract

Purpose

The purpose of this paper is to conduct a numerical analysis of transient turbulent natural convection combined with surface thermal radiation in a square cavity with a local heater.

Design/methodology/approach

The domain of interest includes the air-filled cavity with cold vertical walls, adiabatic horizontal walls and isothermal heater located on the bottom cavity wall. It is assumed in the analysis that the thermophysical properties of the fluid are independent of temperature and the flow is turbulent. Surface thermal radiation is considered for more accurate analysis of the complex heat transfer inside the cavity. The governing equations have been discretized using the finite difference method with the non-uniform grid on the basis of the special algebraic transformation. Turbulence was modeled using the kε model. Simulations have been carried out for different values of the Rayleigh number, surface emissivity and location of the heater.

Findings

It has been found that the presence of surface radiation leads to both an increase in the average total Nusselt number and intensive cooling of such type of system. A significant intensification of convective flow was also observed owing to an increase in the Rayleigh number. It should be noted that a displacement of the heater from central part of the bottom wall leads to significant modification of the thermal plume and flow pattern inside the cavity.

Originality/value

An efficient numerical technique has been developed to solve this problem. The originality of this work is to analyze unsteady turbulent natural convection combined with surface thermal radiation in a square air-filled cavity in the presence of a local isothermal heater. The results would benefit scientists and engineers to become familiar with the analysis of turbulent convective–radiative heat transfer in enclosures with local heaters, and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors and electronics.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Toru Fusegi

A calculation procedure for turbulent natural convection in enclosuresis described. A two‐equation model based on the eddy diffusivityconcept for the temperature field…

Abstract

A calculation procedure for turbulent natural convection in enclosures is described. A two‐equation model based on the eddy diffusivity concept for the temperature field possessing a form similar to the k—ε model of flow is incorporated, thus, extending the applicability of the eddy diffusivity models by removing constraints of the Reynolds analogy between momentum and thermal transport processes. As a test problem, natural convection in a square cavity subjected to differential side‐wall heating is analysed. The vertical walls are divided into isothermal and constant heat‐flux surfaces and heated non‐uniformly. AtRa = 1010 and for an air—filled cavity (Pr = 0.71), variations of heating patterns are found to significantly alter the field characteristics. Numerical predictions demonstrate dissimilar features of the velocity and temperature fluctuations.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 4 no. 6
Type: Research Article
ISSN: 0961-5539

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Article

YONGKE WU and MARCEL LACROIX

Melting of pure metal in presence of turbulent natural convection with Rayleigh number ranging from 106 to 109 has been studied numerically. The governing equations are…

Abstract

Melting of pure metal in presence of turbulent natural convection with Rayleigh number ranging from 106 to 109 has been studied numerically. The governing equations are formulated in terms of stream function—vorticity—temperature and the moving distorted solid/liquid interface is tracked using body‐fitted coordinates. The turbulent flow is taken into account using an algebraic eddy‐viscosity model with Prandtl's mixing length. Results indicate that turbulent natural convection plays a more significant role than laminar flow in the process of melting. Heat transfer and melting rates are significantly increased and a correlation for the average Nusselt number at the heated wall in the quasi‐steady melting regime is proposed.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 2 no. 3
Type: Research Article
ISSN: 0961-5539

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Article

Behrouz Mozafari, Ali Akbar Abbasian Arani, Ghanbar Ali Sheikhzadeh and Mahmoud Salimi

The purpose of this paper is to study the effects of using different Brownian models on natural and mixed convection fluid flow and heat transfer inside the square…

Abstract

Purpose

The purpose of this paper is to study the effects of using different Brownian models on natural and mixed convection fluid flow and heat transfer inside the square enclosure filled with the AlOOH–water nanofluid.

Design/methodology/approach

Due to fulfill of this demand, five different models for the effective thermal conductivity and viscosity of the nanofluid are considered. The following results are presented for the Ra=107 to 1010 and Ri=0.01 to 100, whereas the volume fraction of the nanoparticles is varied from φ = 0.01 to 0.04.

Findings

According to the obtained results, increasing of Rayleigh number and reduction of Richardson number leads to the higher values of the average Nusselt number and entropy generation. Also, it is realized that, variation trend of the average Nusselt number and entropy generation in all cases is increasing by growing the volume fraction. It is found that the obtained average Nusselt numbers and entropy generations with Koo and Kleinstreuer are the highest among all the studied cases, and it is followed by Patel, Vajjha and Das, Corcione and Maxwell–Brinkman models, respectively.

Originality/value

Based on the results of present investigation, the Nusselt number difference predicted between the Maxwell–Brinkman model (as constant-property model) and Koo and Kleinstreuer model is about 7.84 per cent at 0.01 per cent volume fraction and 5.47 per cent at 0.04 per cent volume fraction for the Rayleigh number equal to 107. The entropy generation difference predicted between the two above studied model is about 8.05 per cent at 0.01 per cent volume fraction and 5.86 per cent at 0.04 per cent volume fraction for the Rayleigh number equal to 107. It is observed that using constant-property model has a significant difference in the obtained results with the results of other variable-property models.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 5
Type: Research Article
ISSN: 0961-5539

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Article

M. Ghassemi, M. Fathabadi and A. Shadaram

The paper's purpose is to consider a numerical study of turbulent natural convection heat transfer inside a triangular‐shaped enclosure.

Abstract

Purpose

The paper's purpose is to consider a numerical study of turbulent natural convection heat transfer inside a triangular‐shaped enclosure.

Design/methodology/approach

In the formulation of governing non‐linear partial differential equations the momentum and energy equations coupled with a kε model are applied to the enclosure. To solve these equations, a commercially available computational fluid dynamic (CFD) code, Fluent, is utilized. In addition a control volume‐based code is developed. Finally, the results are compared.

Findings

Flow and temperature field are presented as a function of aspect ratio (Ar), angle between the sloped and horizontal wall (θ) and the Grashof number (Gr). It is shown that heat transfer is higher for turbulent flow when compared with laminar flow. Meanwhile the results reflect a strong dependency on the angle between two enclosure walls (θ). It is clear from the data that the results obtained by CFD code are similar to that of control volume method.

Research limitations/implications

The case considered is two‐dimensional, the motion is two‐dimensional and steady state, the flow is incompressible, the flow is Boussinesq, and the fluid properties are constant. It is recommended to conduct an experimental test in order to validate the analytical results.

Originality/value

The code enables the prediction of the heat transfer inside an attic‐shaped enclosure. This helps in locating the highest area of heat loss; hence prevention can be implemented for this area.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 18 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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