Soufiane Derfoufi, Fayçal Moufekkir and Ahmed Mezrhab
The paper aims to focus on modeling of combined mixed convection and volumetric radiation within a vertical channel using a hybrid thermal lattice Boltzmann method (LBM). The…
Abstract
Purpose
The paper aims to focus on modeling of combined mixed convection and volumetric radiation within a vertical channel using a hybrid thermal lattice Boltzmann method (LBM). The multiple relaxation time LBM (MRT-LBM) is used to compute the dynamical field. The thermal field is determined by a finite difference method (FDM), and the simple relaxation time-LBM (SRT-LBM) serves to calculate the radiative part. The geometry considered concerns a vertical channel defined by two diffuse and isothermal walls. The active fluid represents a gray gas participating in absorption, emission and isotropically scattering. The parametrical study conducted aims to highlight the effect of Richardson number (Ri), Planck number (Pl) and the optical thickness (τ) on dynamical and thermal fields. It is found that radiation affects greatly heat transfer.
Design/methodology/approach
MRT-LBM is used to compute the dynamical field. The thermal field is determined by FDM, and SRT-LBM serves to calculate the radiative part.
Findings
This study has shown the strong capability of this approach to simulate similar problems. The Planck number largely affects the streamlines and isotherms distribution. Also, it causes disappearance of reversal flow, undesirable in most industrial applications, for low Planck numbers. The optical thickness causes the disappearance of reversal flow, in the case in which it appears, for lower opacity. However, for higher opacity it leads to a recurrence of reversed flow.
Originality/value
The use of a new original method composed of MRT-LBM to solve the fluid velocity, FDM to handle the temperature equation and extended SRT-LBM to compute the radiative part of the energy equation.
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A. Mezrhab and M. Bouzidi
This paper describes an approach for the automatic calculation of view factors between surfaces of arbitrary shape, when taking into account possible screening effects due to…
Abstract
Purpose
This paper describes an approach for the automatic calculation of view factors between surfaces of arbitrary shape, when taking into account possible screening effects due to intermediate surfaces.
Design/methodology/approach
The specifically developed numerical code is based on the utilization of boundary elements to fit the surfaces of an algorithm solving the shadow effect and on a Monte Carlo method for the numerical integrations.
Findings
The code has been tested for a set of geometrical configurations. It was clearly shown that it obtains good results in terms of accuracy and computing time. Its accuracy increases when the mesh of radiative surfaces is finer.
Research limitations/implications
The use of the code is limited to opaque surfaces separated by an isothermal semi‐transparent medium which can be absorbent but not diffusing of the thermal radiation.
Practical implications
The study of the radiative exchanges between opaque surfaces with shadow effects due to intermediate surfaces may have concrete practical applications by using this code. Indeed, the code has been used for an industrial application, in order to evaluate view factors inside an enclosure, in the framework of studies concerned with the thermal comfort inside cars.
Originality/value
The originality of this paper lies in taking into account the surfaces of complex geometries by using a boundary elements approximation, the algorithm solving the shadow effect, based on the convexity of the quadrilateral in 2D or the polyhedron in 3D.
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A. Mezrhab, H. Bouali, H. Amaoui and C. Abid
The purpose of this paper is to study the radiation‐natural convection interactions in a vertical divided vented channel. The effects of the surface emissivity, the vent opening…
Abstract
Purpose
The purpose of this paper is to study the radiation‐natural convection interactions in a vertical divided vented channel. The effects of the surface emissivity, the vent opening position and size on the heat transfer and the flow structures inside the channel were studied.
Design/methodology/approach
The governing differential equations are solved by a finite volume method, with adopting the SIMPLER algorithm for pressure‐velocity coupling. The view factors were determined by using a boundary elements approximation and a Monte Carlo method.
Findings
The effect of the radiation exchange is very important, it increases the average hot wall Nusselt number by more than 100 per cent. The contribution of the channel wall emissivity in the heat transfer is more important than that of the plate emissivity. The average hot wall Nusselt number increases with increasing the vent opening size, only in presence of the radiation exchange, and this increase is more pronounced, particularly when the vent opening is located near the channel inlet.
Research limitations/implications
The flow is assumed to be incompressible, laminar and two dimensional. The radiative surfaces are assumed diffuse‐grey. The working fluid, air, is considered as transparent with respect to the radiation.
Practical implications
The industrial applications of this study are solar collectors, thermal building, electronic cooling, aeronautics, chemical apparatus, nuclear engineering, etc.
Originality/value
In comparison to the preceding studies, the originality of this paper is the taking into account of the radiation exchange in a vented and divided channel.
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A. Mezrhab and L. Bchir
The heat transfer by radiation and natural convection in a two‐dimensional, air‐filled square enclosure with a vertical partition of finite thickness and varying height was…
Abstract
The heat transfer by radiation and natural convection in a two‐dimensional, air‐filled square enclosure with a vertical partition of finite thickness and varying height was investigated numerically in the laminar regime. The horizontal end walls are assumed to be adiabatic, and the vertical walls are at different temperatures. Calculations are made by using a finite volume method and an efficient numerical procedure is introduced for calculating the view factors, with shadow effects included. The results indicate that the partition does not significantly modify the heat transfer rate through the cavity, especially at high Rayleigh numbers, provided that its height is less than 90 per cent of the cavity height. The effects of radiation on the velocity and the temperature fields and the overall heat transfer rates as a function of the widths of the vents, solid/fluid conductivity ratio and Rayleigh number are documented.
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H. Bouali and A. Mezrhab
This paper presents a numerical investigation of the interaction of surfaces radiation with developing laminar free convective heat transfer in a divided vertical channel. The…
Abstract
Purpose
This paper presents a numerical investigation of the interaction of surfaces radiation with developing laminar free convective heat transfer in a divided vertical channel. The influence of the radiation on the heat transfer and on the air flow is studied for various sizes (width and length) of the plate.
Design/methodology/approach
The specifically developed numerical code is based on the utilization of the finite volume method. The SIMPLER algorithm for the pressure‐velocity coupling is adopted. The view factors are determined by using boundary elements to fit the surfaces, an algorithm solving the shadow effect and a Monte Carlo method for the numerical integrations.
Findings
Results obtained show that the radiation: plays a very important role on the paces of the isotherms, especially at Ra≥1,600; increases considerably the average wall Nusselt number; and increases the mass flow rate and the average channel Nusselt number at high Rayleigh numbers. The plate location has a significant effect on the heat transfer only in presence of the radiation exchange. The increase of both length and width of the plate causes a decrease of the heat transfer and the mass flow rate.
Research limitations/implications
The use of the code is limited to the flow that is assumed to be incompressible, laminar and two dimensional. The radiative surfaces are assumed diffuse‐gray.
Practical implications
Natural convection in vertical channels formed by parallel plates has received significant attention because of its interest and importance in industrial applications. Some applications are solar collectors, fire research, electronic cooling, aeronautics, chemical apparatus, building constructions, nuclear engineering, etc.
Originality/value
In comparison to the most of the previous studies on natural convection in partitioned channels, the radiation exchange was neglected. This study takes into account the radiation exchange in a divided channel.
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The purpose of this paper is to determine the overall free convective heat transfer coefficient for an assembly constituted by a Quad Flat Non-lead QFN16 welded on a Printed…
Abstract
Purpose
The purpose of this paper is to determine the overall free convective heat transfer coefficient for an assembly constituted by a Quad Flat Non-lead QFN16 welded on a Printed Circuit Board (PCB) which may be inclined with respect to the horizontal plane by an angle varying between 0° and 90° corresponding to the horizontal and vertical position, respectively. This electronic device widely used in electronics generates during its effective operation a power ranging from 0.1 to 0.8 W. The assembly is installed in an air-filled cavity.
Design/methodology/approach
Calculations are done by means of the finite volume method for many configurations obtained by varying the generated power, the inclination angle and the position of the QFN16 on the PCB. The dynamic and thermal aspects are presented and commented.
Findings
The study shows that the thermal state of the electronic device is influenced by the previous three physical parameters. A correlation between the global convective exchange coefficient, the generated power and the PCB inclination angle is proposed in this survey.
Practical implications
The results of this survey allow a better thermal control of this conventional arrangement widely used in electronic applications.
Originality/value
The correlations proposed in this work are original and unpublished. The considered power varies between 0.1 and 0.8W corresponding to the effective operation of the device, associated to a PCB inclination angle ranging between 0° and 90°.
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Daryoush Kamali, Saeid Hejri, Narges Akbar and Emad Hasani Malekshah
The purpose of this study is to present a comprehensive hydrothermal analysis on an inclined mini-channel using numerical and experimental techniques. The fin array acts as heat…
Abstract
Purpose
The purpose of this study is to present a comprehensive hydrothermal analysis on an inclined mini-channel using numerical and experimental techniques. The fin array acts as heat source within the channel, and a wavy wall located at the top of the channel is heat sink. The side walls are insulated with curved profiles. Also, the channel is inclined with four known inclination angles. To solve the governing equations, the dual-multi-relaxation-time lattice Boltzmann method with D2Q9 and D2Q5 lattice models for flow and temperature fields is used, respectively. Also, the channel is filled with SiO2-glycol nanofluid.
Design/methodology/approach
Identifying the behavior of a thermal component during natural convective flow is a challenging topic due to its complexities. This paper focuses on analyzing the thermal and hydrodynamic aspects of a narrow channel equipping with fin array.
Findings
Two correlations are proposed considering temperature and volume fraction ranges for thermal conductivity and dynamic viscosity according to measured experimental data which are used in the numerical phase. Finally, the structure of flow, temperature distribution of fluid, local thermal and viscous dissipations, volume-averaged entropy production, Bejan number and heat transfer rate are extracted by numerical simulations. The results show that the average Nusselt number enhances about 57% (maximum enhancement percentage) when volume fraction increases from 1% to 3% at Ra = 106 and θ = 90°. In addition, the value of entropy generation is maximum at φ = 1%, Ra = 106 and φ = 90°. Also, the maximum enhancement of entropy generation in range of Ra = 103 to 106 is about 4 times at φ = 1% and θ = 90°.
Originality/value
The originality of the present study is combining a modern numerical method (i.e. dual/multi-relaxation-time LBM) with experimental observation on characteristics of SiO2-glycol nanofluid to study the thermal and hydrodynamic properties of the studied mini-channel.
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Muhammet Deveci, Ibrahim Zeki Akyurt and Selahattin Yavuz
The purpose of this paper is to present a new public bread factory location selection for Istanbul Metropolitan Municipality (IMM).
Abstract
Purpose
The purpose of this paper is to present a new public bread factory location selection for Istanbul Metropolitan Municipality (IMM).
Design/methodology/approach
A two-stage methodology is proposed to determine the location for the public bread factory facility. This framework is based on both geographic information systems (GIS) and multi-criteria decision-making (MCDM) techniques. The first stage of the methodology aims to decrease the number of possible alternative locations to simplify the selection activity by applying GIS; the second stage utilises interval type-2 fuzzy MCDM approach to exactly determine the public bread factory site location.
Findings
In this study, the authors present weighted normalised-based interval type-2 hesitant fuzzy and interval type-2 hesitant fuzzy sets (IT2HFSs)-based compressed proportional assessment (COPRAS) methods to overcome facility location selection problem for a fourth public bread factory in Istanbul.
Practical implications
The results show that the proposed approach is practical and can be employed by the bakery industry.
Originality/value
In this study, the authors present a two-stage methodology for public bread factory site selection. In the first stage, the number of alternatives is reduced by the GIS. In the second stage, an interval type-2 fuzzy set is implemented for the evaluation of public bakery factory site alternatives. A new integrated approach based on COPRAS method and weighted normalised with IT2HFSs is proposed.
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Abimanyu Purusothaman, Abderrahmane Baïri and Nagarajan Nithyadevi
The purpose of this paper is to examine numerically the natural convection heat transfer in a cubical cavity induced by a thermally active plate. Effects of the plate size and its…
Abstract
Purpose
The purpose of this paper is to examine numerically the natural convection heat transfer in a cubical cavity induced by a thermally active plate. Effects of the plate size and its orientation with respect to the gravity vector on the convective heat transfer and the flow structures inside the cavity are studied and highlighted.
Design/methodology/approach
The numerical code is based on the finite volume method with semi-implicit method for pressure-linked equation algorithm. The convective and diffusive terms in momentum equations are handled by adopting the power law scheme. Finally, the discretized sets of algebraic equations are solved by the line-by-line tri-diagonal matrix algorithm.
Findings
The results show that plate orientation and size plays a significant role on heat transfer. Also, the heat transfer rate is an increasing function of Rayleigh number for both orientations of the heated plate. Depending on the thermal management of the plate and its application (as in electronics), the heat transfer rate is maximized or minimized by selecting appropriate parameters.
Research limitations/implications
The flow is assumed to be 3D, time-dependent, laminar and incompressible with negligible viscous dissipation and radiation. The fluid properties are assumed to be constant, except for the density in the buoyancy term that follows the Boussinesq approximation.
Originality/value
The present work will give some additional knowledge in designing sealed cavities encountered in some engineering applications as in aeronautics, automobile, metallurgy or electronics.
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Mikhail A. Sheremet, Ioan Pop and Alin V. Rosca
The purpose of this study is a numerical analysis of transient natural convection in an inclined square cavity filled with an alumina-water nanofluid under the effects of…
Abstract
Purpose
The purpose of this study is a numerical analysis of transient natural convection in an inclined square cavity filled with an alumina-water nanofluid under the effects of sinusoidal wall temperature and thermal radiation by using a single-phase nanofluid model with empirical correlations for effective viscosity and thermal conductivity.
Design/methodology/approach
The domain of interest includes the nanofluid-filled cavity with a sinusoidal temperature distribution along the left vertical wall. Horizontal walls are supposed to be adiabatic, while right vertical wall is kept at constant low temperature. Temperature of left wall varies sinusoidally along y-coordinate. It is assumed in the analysis that the thermophysical properties of the fluid are independent of temperature and the flow is laminar. The governing equations have been discretized using the finite difference method with the uniform grid. Simulations have been carried out for different values of the Rayleigh number, cavity inclination angle, nanoparticles volume fraction and radiation parameter.
Findings
It has been found that a growth of radiation parameter leads to the heat transfer enhancement and convective flow intensification. At the same time, an inclusion of nanoparticles illustrates a reduction in the average Nusselt number and fluid flow rate.
Originality/value
The originality of this work is to analyze unsteady natural convection in a square cavity filled with a water-based nanofluid in the presence of a sinusoidal temperature distribution along one wall. The results would benefit scientists and engineers to become familiar with the analysis of convective heat and mass transfer in nanofluids and the way to predict the properties of nanofluid convective flow in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.