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Article
Publication date: 15 May 2009

Manab Kumar Das and Pravin Shridhar Ohal

The purpose of this paper is to investigate the behaviour of nanofluids numerically inside a partially heated and partially cooled square cavity to gain insight into heat transfer…

570

Abstract

Purpose

The purpose of this paper is to investigate the behaviour of nanofluids numerically inside a partially heated and partially cooled square cavity to gain insight into heat transfer and flow processes induced by a nanofluid.

Design/methodology/approach

A model is developed to analyze the behaviour of nanofluids taking into account the solid volume fraction χ. The transport equations are solved numerically with finite volume approach using SIMPLEC algorithm.

Findings

Comparisons with previously published work on the basis of special cases are performed and found to be in excellent agreement. Five different relative positions of the active zones are considered.While circulation depend strongly on the total exit length. Governing parameters were 103 < Gr < 107 but due to space constraints the results for 104 < Gr <107 are presented. It is found that both the Grashof number and solid volume fraction χ affect the fluid flow and heat transfer in the cavity. CopperWater nanofluid is used with Pr = 6.2 and solid volume fraction is varied as 0, 4, 8, 12, 16 and 20 per cent. Detailed results are presented for flow pattern and heat transfer curves.

Originality/value

The present study focusses on the analysis of several parameters on the heat transfer characteristics of nanofluids within the enclosure.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 3/4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 15 May 2009

Elaprolu Vishnuvardhanarao and Manab Kumar Das

The purpose of this paper is to consider a two‐dimensional, steady, mixed convection flow in an enclosure filled with a fluid‐saturated uniform porous medium. The left wall is…

545

Abstract

Purpose

The purpose of this paper is to consider a two‐dimensional, steady, mixed convection flow in an enclosure filled with a fluid‐saturated uniform porous medium. The left wall is moving down and the right wall is moving up and are maintained at cold and hot constant temperatures, respectively. The top and the bottom walls are fixed and are thermally insulated.

Design/methodology/approach

The governing equations are normalized and solved numerically with appropriate boundary conditions by finite‐volume approach using third‐order accurate scheme (deferred QUICK).

Findings

The study is conducted by varying the key parameters, i.e. Richardson number (Ri=Gr/Re2), Darcy number (Da=κ /H2) and Grashof number (Gr=gβ H3 Δ T2) and fixing Prandtl number at (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 gradually increased for Gr up to 103. The asymptotic value is 1.5 for Gr=104. A heat transfer correlation is also presented.

Originality/value

The study of the mixed convection problem with lid‐driven flows in enclosures will be useful in cooling of electronic devices, lubrication technologies, chemical processing equipment, etc.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 3/4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 9 January 2009

E. Vishnuvardhanarao and Manab Kumar Das

The purpose of this paper is to consider the conjugate heat transfer from a flat plate involving a turbulent plane wall jet. The bottom wall of the solid block is heated by a…

463

Abstract

Purpose

The purpose of this paper is to consider the conjugate heat transfer from a flat plate involving a turbulent plane wall jet. The bottom wall of the solid block is heated by a constant heat flux.

Design/methodology/approach

High Reynolds number two‐equation model (κϵ) has been used for turbulence modeling. The parameters considered are the conductivity ratio of solid and fluid, the solid slab thickness and the Prandtl number. The Reynolds number considered is 15,000 because the flow becomes fully turbulent and then is independent of the Reynolds number. The range of parameters considered are: conductivity ratio = 1‐1,000, solid slab thickness = 1‐10 and Prandtl number = 0.01‐100.

Findings

The non‐dimensional bottom surface temperature is high for high‐Prandtl number fluid and vice versa. As conductivity ratio increases, it decreases whereas it increases with the increase in slab thickness. Similar trend is observed for the distribution of the interface temperature. The Nusselt number computed based on the interface temperature increases with Prandtl number. It is observed that for the range of parameters considered, local Nusselt number distribution superimposes with each other. The average heat flux at the interface has been computed and found to be equal with average heat flux at the bottom which ensures the overall heat balance.

Originality/value

The study of conjugate heat transfer with a turbulent wall jet will be useful for cooling of heated body.

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
Publication date: 6 November 2007

Manab Kumar Das and P. Rajesh Kanna

The purpose of the paper is to study the steady and periodic solution of a lid‐driven cavity flow problem with the gradual increase of Reynolds number (Re) up to 10,000.

875

Abstract

Purpose

The purpose of the paper is to study the steady and periodic solution of a lid‐driven cavity flow problem with the gradual increase of Reynolds number (Re) up to 10,000.

Design/methodology/approach

The problem is solved by unsteady stream function‐vorticity formulation using the clustered grids. The alternating direction implicit (ADI) method and the central difference scheme have been used for discretization of the governing equations. Total vorticity error and the total kinetic energy have been considered for ensuring the state of flow condition. The midplane velocity distribution and the top wall vortex distribution are compared with the results of other authors and found to show good agreement.

Findings

Kinetic energy variation with time is studied for large time computation. Below 7,500, it becomes constant signifying the flow to be in steady‐state. At Re=10,000, the fluid flow has an oscillating nature. The dimensionless period of oscillation is found to be 1.63. It is demonstrated that the present computation is able to capture the periodic solution after the bifurcation very accurately.

Originality/value

The findings will be useful in conducting a steady and periodic solution of variety of fluid flows or thermally‐driven fluid flows.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 17 no. 8
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 25 February 2014

Shantanu Pramanik and Manab Kumar Das

The purpose of the present study is to investigate the flow and turbulence characteristics of a turbulent wall jet flowing over a surface inclined with the horizontal and to…

407

Abstract

Purpose

The purpose of the present study is to investigate the flow and turbulence characteristics of a turbulent wall jet flowing over a surface inclined with the horizontal and to investigate the effect of variation of the angle of inclination of the wall on the flow structure of the wall jet.

Design/methodology/approach

The high Reynolds number two-equation κ− model with standard wall function is used as the turbulence model. The Reynolds number considered for the present study is 10,000. The Reynolds averaged Navier-Stokes (RANS) equations are used for predicting the turbulent flow. A staggered differencing technique employing both contravariant and Cartesian components of velocity has been applied. Results for distribution of wall static pressure and skin friction, decay of maximum streamwise velocity, streamwise variation of integral momentum and energy flux have been compared for the cases of α=0°, 5°, and 10°.

Findings

Flow field has been represented in terms of streamwise and lateral velocity contours, static pressure contour, vorticity contour and streamwise velocity and static pressure profiles at different locations along the oblique offset plate. Distribution of Reynolds stresses in terms of spanwise, lateral and turbulent shear stresses, and turbulent kinetic energy and its dissipation rate have been presented to describe the turbulent characteristics. Similarity of streamwise velocity and the velocity parallel to the oblique wall has been observed in the developed region of the wall jet flow. A decaying trend is observed in the variation of total integral momentum flux in the developed region of the wall jet which becomes more evident with increase in oblique angle. Developed flow region has indicated trend of similarity in profiles of streamwise velocity as well as velocity component parallel to the oblique wall. A depression in wall static pressure has been observed near the nozzle exit when the wall is inclined and the depression increases with increase in inclination. Effect of variation of oblique angles on skin friction coefficient has indicated that it decreases with increase in oblique angle. Growth of the outer and inner shear layers and spread of the jet shows linear variation with distance along the oblique wall. Decay of maximum streamwise velocity is found to be unaffected by variation in oblique angle except in the far downstream region. The streamwise variation of spanwise integral energy shows increase in oblique angle and decreases the magnitude of energy flux through the domain. In the developed flow region, streamwise variation of centreline turbulent intensities shows increased values with increase in oblique angle, while turbulence intensities along the jet centreline in the region X<12 remain unaffected by change in oblique angles. Normalized turbulent kinetic energy distribution highlights the difference in turbulence characteristics between the wall jet and reattached offset jet flow. Near wall velocity distribution shows that the inner region of boundary layer of the developed oblique wall jet follows a logarithmic profile, but it shows some difference from the standard logarithmic curve of turbulent boundary layers which can be attributed to an increase in skin friction coefficient and a decrease in thickness of the wall attached layer.

Originality/value

The study presents an in-depth investigation of the interaction between the jet and the inclined wall. It is shown that due to the Coanda effect, the jet follows the nearby wall. The findings will be useful in the study of combined flow of wall jet and offset jet and dual offset jet on oblique surfaces leading to a better design of some mechanical jet flow devices.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 2
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 21 October 2021

Masoud Nakhaei Ashtari and Mariana Correia

The aim of this research is to evaluate the vulnerability of earthen heritage when facing climate change, by focusing on Tchogha Zanbil site as a case study – an outstanding…

241

Abstract

Purpose

The aim of this research is to evaluate the vulnerability of earthen heritage when facing climate change, by focusing on Tchogha Zanbil site as a case study – an outstanding example of an earthen site that recurrently faces extreme climatic events. Moreover, the adaptive capacity of traditional knowledge and ancient systems is also evaluated, in order to contribute for future climate change adaptation planning.

Design/methodology/approach

The vulnerability of cultural heritage to climate change was considered as the degree to which an identified cultural heritage value was susceptible to, or would be adversely affected by, the effects of climate change, including climate variability and extreme temperatures. In order to establish a vulnerability assessment, this paper will assess different definitions regarding vulnerability, exposure and sensitivity, crossing it with indicators of physical parameters, in order to propose an adaptive capacity for the site, based on ancient traditional knowledge.

Findings

Nonetheless, the entailed research helped establish a framework that contributes to outline the vulnerability and the potential for adaptive capacity of World Heritage properties, especially earthen sites located in regions exposed to rising climate change impact.

Research limitations/implications

The research faced some limitations regarding access to data and to site visits, due to COVID-19 restrictions that were in place.

Originality/value

This research presents a methodological assessment of climate change risk in Tchogha Zanbil, a World Heritage earthen site in Iran, representative of a property highly exposed to risk and vulnerability.

Details

Journal of Cultural Heritage Management and Sustainable Development, vol. 12 no. 2
Type: Research Article
ISSN: 2044-1266

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Article
Publication date: 17 July 2023

Shabeer Khan, Mohd Ziaur Rehman, Mohammad Rahim Shahzad, Naimat U Khan and Lutfi Abdul Razak

There has been a burgeoning interest in exploring the impact of uncertainty factors on share returns. However, studies on the influence of global financial uncertainties on…

257

Abstract

Purpose

There has been a burgeoning interest in exploring the impact of uncertainty factors on share returns. However, studies on the influence of global financial uncertainties on emerging market sectoral indices are scarce. Thus, there is a need to have a thorough investigation of the connection between global financial uncertainties and emerging market sectoral indices. To fill this gap, using the theoretical framework of international portfolio diversification (IPD) and utilizing data from 2008 to 2021, this study examines the spillover connection between global uncertainty indices (GUIs) and leading sectoral indices of 28 emerging markets.

Design/methodology/approach

The authors employ the quantile spillover-based connectedness approach and minimum connectedness portfolio approach to explore the dynamic connectedness among sectoral indices and global uncertainty indices (GUIs) as well as portfolio implication.

Findings

The study found high connectedness among all indices, especially at higher and lower quantiles. Among GUIs, the authors find that stock market volatility (VIX) and oil volatility index (OVX) are strongly interconnected with all leading emerging markets' sectoral indices. Among sectoral indices, the linkage between the financial (F-Index), information technology (IT-Index), and consumer discretionary (CD-Index) sectors shows moderate interconnectedness. In contrast, the communication services (CS-Index) sector has low interconnectedness with the system. In terms of spillover effects, the authors find EVZ, OVX, and the IT sectors to be net recipients for the entire period. The authors also explored portfolio diversification benefits by employing a minimum connectedness portfolio approach. The cumulative returns' findings show a slight decline in the portfolio's value after 2010; during 2012, the pattern remained stable; from 2014 to 2020, the portfolio performed negatively, that is, underperformance due to different events in that period, including COVID-19. The Consumer Discretionary sector is found to be significant because of having the largest weight, 51%, in the portfolio during the study period.

Practical implications

The study suggests that investors should invest in the communication services sector as it is the least connected. However, the connectedness increases during COVID-19, which implies that it may be difficult for investors to benefit from IPD in a crisis period. Hence, to obtain the benefits from IPD, the evidence suggests that investors need to consider Consumer Discretionary sector while considering assets for investment.

Originality/value

The study's uniqueness is that the authors have investigated spillover between GUIs and 28 emerging markets sectoral indices by employing a quantile spillover-based connectedness approach and minimum connectedness portfolio approach with a special focus on portfolio implication.

Details

International Journal of Emerging Markets, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1746-8809

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Article
Publication date: 24 April 2024

Mohamed Moshreh Ali Ahmed, Dina Kamal Abd El Salam Ali Hassan and Nourhan Hesham Ahmed Magar

The purpose of this paper is to investigate whether audit committee characteristics, in particular audit committee size, audit committee activity and audit committee gender…

806

Abstract

Purpose

The purpose of this paper is to investigate whether audit committee characteristics, in particular audit committee size, audit committee activity and audit committee gender diversity, are associated with financial performance in Egyptian banks. The second purpose of this paper is to explore the moderating role of board gender diversity on the relationship between audit committee characteristics and financial performance.

Design/methodology/approach

A multiple regression analysis is used to estimate the moderating role of board gender diversity on the relationship between audit committee characteristics and financial performance of a sample of Egyptian banks during the period between 2018 and 2022.

Findings

The results indicate that audit committee size has a negative and insignificant effect impact on return on assets (ROA) and return on equity (ROE), respectively. The results also indicate that the audit committee gender diversity has a significant positive impact on ROA and ROE, respectively. Regarding audit committee activity, the number of board meetings has a negative and insignificant effect on ROA and ROE, respectively. Regarding gender diversity as a moderating variable, in general there is a positive effect of gender diversity on the relationship between audit committee characteristics and financial performance.

Research limitations/implications

The study was limited to 20 banks in one country, but it sets the tone for future empirical research on this subject matter. The study also relied on one moderating variable, which is board gender diversity. This study provides an avenue for future research in the area of corporate governance and financial performance in other emerging countries, especially other African countries.

Practical implications

This study provides useful insights for managers and policymakers to better understand which audit committee characteristics can best encourage a company to improve financial performance. Furthermore, regulators should ensure that banks strictly adhere to corporate governance principles to build a strong banking industry capable of achieving economic development.

Social implications

Banks will benefit equally from valuable qualities across demographic groupings in society by having females on the audit committee and appropriate audit committee meetings. Additionally, if audit committee members are correctly selected, banks with more females in audit committee and suitable audit committee meetings can successfully contribute to strengthening financial performance and social welfare of diverse segments of society. A culture of good banking governance must emerge to improve bank financial stability and, as a result, greater stability and economic growth.

Originality/value

To the best of the authors’ knowledge, the study is, perhaps, the first to examine the moderating role of board gender diversity on the relationship between audit committee characteristics and financial performance in Egyptian banks. This study adds to the literature by investigating such an issue in a developing economy that operates in a different context than those in developed countries.

Details

Journal of Financial Reporting and Accounting, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1985-2517

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