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Article
Publication date: 1 March 2003

S. Kasbioui, E.K. Lakhal and M. Hasnaoui

The investigation of heat transfer and fluid flow by mixed convection in a vertical rectangular cavity containing adiabatic partitions attached to the heated wall is numerically…

375

Abstract

The investigation of heat transfer and fluid flow by mixed convection in a vertical rectangular cavity containing adiabatic partitions attached to the heated wall is numerically studied. The parameters governing this problem are the Rayleigh number (103≤Ra≤4×105), the Reynolds number (5≤Re≤100), the aspect ratio of the cavity (2.5≤A≤15), the partitions length (0.1≤B≤0.95), the aspect ratio of the micro cavities (0.33≤C≤0.66) and the Prandtl number (Pr=0.72). The results obtained indicate that the heat exchange between the system and the external medium, through the cold wall and the upper vent, are considerably affected by the presence of the partitions and for all the values of A and Ra considered. However, the quantity of heat released by the higher opening remains insensitive to the presence of the partitions; it depends only on the intensity of the forced flow. Moreover, it is shown that for critical values of Re and Ra, these rates of heat transfer pass by maxima of which the value is independent of A when this parameter is equal to or higher than 10. For high Reynolds numbers, the flow is dominated by forced convection for low values of Ra and high values of B. Finally, the competition between natural and forced convection occurs when Ra≥104. The heat transfer is correlated with the main parameters and presented for an eventual utilization in design.

Details

Engineering Computations, vol. 20 no. 2
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 9 January 2020

Lei Wang, Yang Cai, Wei-Wei Wang, Run-Zhe Liu, Di Liu, Fu-Yun Zhao and Hanqing Wang

This paper aims to numerically investigate the magnetohydrodynamic (MHD) convection heat transfer of nanofluid inside a differentially heated enclosure with various fin…

216

Abstract

Purpose

This paper aims to numerically investigate the magnetohydrodynamic (MHD) convection heat transfer of nanofluid inside a differentially heated enclosure with various fin morphologies.

Design/methodology/approach

The fluid flow within the cavity was governed by N-S equations while it within porous medium was solved by the non-Darcy model, called the Darcy–Forchheimer model based on representative element-averaging method. Empirical correlations from experimental data are used to evaluate the effective thermal conductivity and dynamic viscosity. Relevant governing parameters, including thermal Rayleigh number (105-107), Hartmann number (0-50), Darcy number (10−6-10−1), thermal conductivity ratio of porous matrix (1-103), nanoparticles volume fraction (0-0.04) and topology designs of porous fins, are sensitively varied to identify their effects and roles on the fluid flow and heat transfer. Particularly, heatlines are used to investigate the mechanism of heat transport.

Findings

Numerical results demonstrate that the predictions of average Nusselt number are augmented by using more porous fins with high permeability, and this effect becomes opposite in tiny Darcy numbers. Particularly, for high Darcy and Rayleigh numbers, the shortest fins could achieve the best performance of heat transfer. In addition, the prediction of average Nusselt number reduces with an increase in Hartmann numbers. An optimal nanoparticles concentration also exists to maximize heat transfer enhancement. Finally, numerical correlations for the average Nusselt number were proposed as functions of these governing parameters.

Practical implications

Present work could benefit the thermal design of electronic cooling and thermal carriers in nanofluid engineering.

Social implications

Present work could benefit the thermal design of electronic cooling and thermal carriers in nanofluid engineering. In addition, optimum thermal removals could enhance the lifetime of electronics, therefore reducing the cost of energy and materials.

Originality/value

To the best knowledge of authors, there are not any studies considering the synergetic effects of porous fins on MHD convection of nanofluids. Present work could benefit the thermal design of electronic cooling and thermal carriers in nanofluid engineering.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 8
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 9 April 2019

Fatih Selimefendigil, Hakan F. Öztop and Ali J. Chamkha

This paper aims to numerically examine the mixed convection of SiO2-water nanofluid flow in a three-dimensional (3D) cubic cavity with a conductive partition considering various…

358

Abstract

Purpose

This paper aims to numerically examine the mixed convection of SiO2-water nanofluid flow in a three-dimensional (3D) cubic cavity with a conductive partition considering various shapes of the particles (spherical, cylindrical, blade, brick). The purpose is to analyze the effects of various pertinent parameters such as Richardson number (between 0.1 and 10), Hartmann number (between 0 and 10), solid nanoparticle volume fraction (between 0 and 0.04), particle shape (spherical, cylindrical, blade, brick) and different heights and lengths of the conductive partition on the fluid flow and heat transfer characteristics.

Design/methodology/approach

The numerical simulation was performed by using Galerkin-weighted residual finite element method for various values of Richardson number, Hartmann number, solid nanoparticle volume fraction, particle shape (spherical, cylindrical, blade, brick) and different heights and lengths of the conductive partition. Two models for the average Nusselt number were proposed for nanofluids with spherical and cylindrical particle by using multi-layer feed-forward neural networks.

Findings

It was observed that the average Nusselt number reduces for higher values of Richardson number and Hartmann number, while enhances for higher values of nanoparticle volume fraction. Among various types of particle shapes, blade ones perform the worst and cylindrical ones perform the best in terms of heat transfer enhancement, but this is not significant which is less than 3 per cent. The average Nusselt number deteriorates by about 6.53per cent for nanofluid at the highest volume fraction of spherical particle shapes, but it is 11.75per cent for the base fluid when Hartmann number is increased from 0 to 10. Conductive partition geometrical parameters (length and height) do not contribute to much to heat transfer process for the 3D cavity, except for the case when height of the partition reaches 0.8 times the height of the cubic cavity, the average Nusselt number value reduces by about 25per cent both for base fluid and for nanofluid when compared to case with cavity height which is 0.2 times the height of the cubic cavity.

Originality/value

Based on the literature survey, a 3D configuration for MHD mixed convection of nanofluid flow in a cavity with a conductive partition considering the effects of various particle shapes has never been studied in the literature. This study is a first attempt to use a conductive partition with nanofluid of various particle shapes to affect the fluid flow and heat transfer characteristics in a 3D cubic cavity under the influence of magnetic field. Partial or all findings of this study could be used for the design and optimization of realistic 3D thermal configurations that are encountered in practice and some of the applications were already mentioned above. In this study, thermal performance of the system was obtained in terms of average heat transfer coefficient along the hot surface, and it is modeled with multi-layer feed-forward neural networks.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 10
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 15 June 2022

Mounir Kouhila, Younes Bahammou, Hamza Lamsyehe, Zakaria Tagnamas, Haytem Moussaoui, Ali Idlimam and Abdelkader Lamharrar

The paper aims to evaluate drying performance of earth mortar by solar drying for more durability, minimize pathologies in traditional construction and determine the influence of…

67

Abstract

Purpose

The paper aims to evaluate drying performance of earth mortar by solar drying for more durability, minimize pathologies in traditional construction and determine the influence of temperature and humidity on the microstructure of earth mortar using static gravimetric method.

Design/methodology/approach

A convective solar dryer was used for the pretreatment of building and solid materials for construction.

Findings

The humidity influences the mortar sorption – surface water sorption of earth mortar increased with increasing temperature.

Originality/value

The study used a novel method for pretreatment building materials by using solar dryer.

Details

International Journal of Building Pathology and Adaptation, vol. 42 no. 5
Type: Research Article
ISSN: 2398-4708

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Article
Publication date: 12 June 2009

S.Z. Shuja, B.S. Yilbas and S.M.A. Khan

The purpose of this paper is to consider flow over heat generating bodies in an open‐ends cavity, which finds applications in electronics cooling and industrial processing. Heat…

373

Abstract

Purpose

The purpose of this paper is to consider flow over heat generating bodies in an open‐ends cavity, which finds applications in electronics cooling and industrial processing. Heat transfer rates depend on the flow situation in the cavity, which is influenced by the cavity inlet and exit port locations, heat transferring body size and its orientation in the cavity, and the cavity size. Consequently, modeling of flow over heat transferring bodies in an open‐ends cavity and examination of the effect of the aspect ratio and orientation of the heat transferring bodies on the flow field and heat transfer rates becomes essential.

Design/methodology/approach

The flow over heat generating solid blocks situated in an open‐ends cavity is considered and the effects of blocks' orientations and aspect ratios on flow field as well as heat transfer rates are examined. A numerical scheme using a control volume approach is introduced to predict flow field in the cavity and heat transfer rates from the blocks.

Findings

It is found that complex flow structure is generated in the cavity due to the aspect ratios and orientations of the blocks. This, in turn, influences significantly heat transfer rates from the blocks in the cavity.

Research limitations/implications

Surface areas of blocks are kept the same and aspect ratio is varied such that the surface area of each block remains the same in the simulations. In addition, Steady flow situation is considered for governing equations of flow and heat transfer in the cavity. However, for the future study transient heating and flow situations can be considered while varying the surface araes of the blocks. This will provide useful information on the circulations in the cavity and the enhancement of heat transfer due to the complex flow structure.

Practical implications

In practice, cooling effectiveness can be improved through changing the aspects ratio of the heat generating bodies in the cavity.

Originality/value

The findings are original and will be useful for the scientists and the design engineers working the specific area of heat transfer and fluid flow.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 5
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 6 June 2016

Abderrahmane Baïri

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…

236

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°.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 5
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 7 November 2016

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…

285

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.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 8
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 30 May 2024

Bilel Bzeouich, Florence Depoers and Faten Lakhal

The purpose of this paper is to examine the effect of chief executive officer (CEO) overconfidence on earnings quality and the moderating role of ownership structure as a crucial…

293

Abstract

Purpose

The purpose of this paper is to examine the effect of chief executive officer (CEO) overconfidence on earnings quality and the moderating role of ownership structure as a crucial corporate governance device.

Design/methodology/approach

The paper uses the generalized method of moments (GMM) estimation method to test our models on a sample of 335 French companies between 2009 and 2020, i.e. 4,020 observations.

Findings

The results show that CEO overconfidence negatively affects earnings quality. This result supports the predictions of behavioral finance theory and suggests that CEO overconfidence is a behavioral bias that affects the quality of earnings. The authors also examined the effect of different types of ownership structures on this relationship. The results show the significant role of controlling shareholders, owner-managers, families and institutional investors in mitigating the negative effect of CEO overconfidence on earnings quality.

Research limitations/implications

This paper has some limitations. First, other types of ownership structures could have been analyzed such as state ownership. Second, we ignored the role of the board of directors as an important governance mechanism in controlling overconfident CEOs’ actions.

Practical implications

Companies should be aware of the potential risks associated with CEO overconfidence, which can compromise the faithful representation of earnings. This highlights the importance of effective monitoring and internal controls to detect and prevent such practices, which involve the role of ownership structure.

Originality/value

This paper addresses the effect of CEO overconfidence on earnings quality and provides new evidence on the role of different ownership structure types in shaping this relationship. Additionally, this paper sheds new light on how overconfident CEOs may behave in challenging times.

Details

Journal of Applied Accounting Research, vol. 26 no. 1
Type: Research Article
ISSN: 0967-5426

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Article
Publication date: 1 January 2024

Oumayma Tajouri and Lassaad Lakhal

This article examines the direct effect of total quality management (TQM) practices on organizational performance (OP) and innovation (INN), as well as their indirect effect…

704

Abstract

Purpose

This article examines the direct effect of total quality management (TQM) practices on organizational performance (OP) and innovation (INN), as well as their indirect effect through organizational learning (OL) as a mediating variable. In addition, this survey examines company size as a contextual variable in the relationship between TQM and outcome variables.

Design/methodology/approach

A conceptual framework is proposed to test causal links between TQM, OP, INN and OL. To empirically test this framework, 110 questionnaires were collected from large Tunisian quality-certified industries, and 167 questionnaires were collected from small and medium-sized industries (SMIs) in order to examine the effect of company size. In this order, a multigroup analysis (MGA) is performed.

Findings

Using the structural equation modeling technique, seven hypotheses are investigated. The results reveal that TQM has a direct and significant positive effect on OP and INN. Data analysis shows that there is a significant positive effect between TQM and OL, while OL positively influences OP and INN. Furthermore, the results illustrate a mediating effect of OL between TQM and OP and INN. The results reveal that large industries and SMIs show significant differences in the relationship, including the conceptual model.

Practical implications

The conceptual framework can be used by practitioners for effective implementation of TQM practices to simultaneously improve operational performance, quality performance and INN. This study also focuses on the role of OL in large-scale industries.

Originality/value

While the relationships between TQM, INN and OP have been examined separately in previous studies, this study examines the relationship between these variables in a unique model in Tunisian industries, including OL as a mediating variable. In addition, it is one of the few studies that considers firm size as a contextual variable and provides an analysis of its effect on the relationships between these variables. This study presents new data and empirical insights into the relationship between these variables.

Details

International Journal of Quality & Reliability Management, vol. 41 no. 6
Type: Research Article
ISSN: 0265-671X

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Article
Publication date: 20 February 2024

Giammarco Marras, Matteo Opizzi and Michela Loi

The aim of this study is to systematise the entrepreneurial coaching (EC) literature by understanding how the phenomenon has been investigated along four dimensions inspired by…

282

Abstract

Purpose

The aim of this study is to systematise the entrepreneurial coaching (EC) literature by understanding how the phenomenon has been investigated along four dimensions inspired by Gartner’s (1985) conceptualisation of entrepreneurship: entrepreneurial process, context, target and outcomes. In so doing, this study will provide a frame of its multifunctional role and identify relevant gaps and suggestions for future research.

Design/methodology/approach

We conducted a systematic literature review to collect existing works on EC. We analysed 85 selected papers with a qualitative content analysis that allowed us to highlight relevant research themes for the entrepreneurial process, context, outcomes and target.

Findings

Our results demonstrate that EC has a multifunctional role in entrepreneurship that can be summarised in five different typologies, depending on the stage of the entrepreneurial process in which it is applied, the context, the target and the outcomes.

Originality/value

As one of the first attempts to systematise studies on EC, this work extends previous conceptualisation of EC by detailing different typologies of this intervention, thereby contributing to reduced fragmentation and conceptual ambiguity.

Details

Journal of Managerial Psychology, vol. 39 no. 6
Type: Research Article
ISSN: 0268-3946

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