Search results
1 – 10 of over 1000T. BO and H. IACOVIDES
This article examines the influence of centrifugal buoyancy on the hydrodynamic and thermal behaviour in fully developed flow through an orthogonally rotating duct of aspect ratio…
Abstract
This article examines the influence of centrifugal buoyancy on the hydrodynamic and thermal behaviour in fully developed flow through an orthogonally rotating duct of aspect ratio 2:1. A series of computations have been performed at rotation numbers ranging from 0 to 0.2, for constant‐density flows (no buoyancy) and also for different levels of outward and inward buoyancy. The resulting comparisons reveal that for a Reynolds number of 32,500, rotational buoyancy effects become significant at Rayleigh number values greater than 107. In outward flows, buoyancy is found to strengthen the effects of the Coriolis force on the mean motion and, by raising turbulence levels, buoyancy also enhances wall heat transfer along both the pressure and the suction side of the rotating duct. In inward flows, it is found that strong buoyancy can reverse the direction of the Coriolis‐induced secondary motion, which causes a strong rise in wall heat transfer along the suction side and a similarly significant fall in heat transfer along the pressure side. The computed effects on heat transfer are in qualitative agreement with the findings of a number of experimental studies. For both inward and outward flows, at a constant Reynolds number, the modifications of centrifugal buoyancy on the side‐averaged levels of heat transfer correlate reasonably well with the rotational Rayleigh number.
Details
Keywords
Esmail M.A. Mokheimer, S. Sami and B.S. Yilbas
This paper's aim is to examine flow and heat transfer through vertical channels between parallel plates, which is of prime importance in the design of cooling systems for…
Abstract
Purpose
This paper's aim is to examine flow and heat transfer through vertical channels between parallel plates, which is of prime importance in the design of cooling systems for electronic equipment such as that of finned cold plates in general, plate‐and‐frame heat exchangers, etc.
Design/methodology/approach
Numerical and analytical solutions are presented to investigate the heat transfer enhancement and the pressure drop reduction due to buoyancy effects (for buoyancy‐aided flow) for the developing laminar mixed convection in vertical channel between parallel plates in the vicinity of the critical values of the buoyancy parameter (Gr/Re)crt that are obtained analytically. The numerical solutions are presented for a wide range of the buoyancy parameters Gr/Re that cover both of buoyancy‐opposed and buoyancy‐aided flow situations under each of the isothermal boundary conditions under investigation.
Findings
Buoyancy parameters greater than the critical values result in building‐up the pressure downstream of the entrance such that the vertical channel might act as a thermal diffuser with possible incipient flow reversal. Locations at which the pressure gradient vanishes and the locations at which the pressure‐buildup starts have been numerically obtained and presented for all the investigated cases.
Research limitations/implications
The study is limited to the laminar flow situation.
Practical implications
The results clearly show that for buoyancy‐aided flow, the increase of the buoyancy parameter enhances the heat transfer and reduces the pressure drop across the vertical channel. These findings are very useful for cooling channel or chimney designs.
Originality/value
The study is original and presents new findings, since none of the previous studies reported the conditions for which pressure buildup might take place due to mixed convection in vertical channels between parallel plates.
Details
Keywords
The aim of this article is to present the results of a parametric analysis of the entropy generation due to mixed convection in the entry‐developing region between two…
Abstract
Purpose
The aim of this article is to present the results of a parametric analysis of the entropy generation due to mixed convection in the entry‐developing region between two differentially heated isothermal vertical plates.
Design/methodology/approach
The entropy generation was estimated via a numerical solution of the mass, momentum and energy conservation equations governing the flow and heat transfer in the vertical channel between the two parallel plates. The resultant temperature and velocity profiles were used to estimate the entropy generation and other heat transfer parameters over a wide range of the operating parameters. The investigated parameters include the buoyancy parameter (Gr/Re), Eckert number (Ec), Reynolds number (Re), Prandtl number (Pr) and the ratio of the dimensionless temperature of the two plates (θT).
Findings
The optimum values of the buoyancy parameter (Gr/Re) optimum at which the entropy generation assumes its minimum for the problem under consideration have been obtained numerically and presented over a wide range of the other operating parameters. The effect of the other operating parameters on the entropy generation is presented and discussed as well.
Research limitations/implications
The results of this investigation are limited to the geometry of vertical channel parallel plates under isothermal boundary conditions. However, the concept of minimization of entropy generation via controlling the buoyancy parameter is applicable for any other geometry under any other thermal boundary conditions.
Practical implications
The results presented in this paper can be used for optimum designs of heat transfer equipment based on the principle of entropy generation minimization with particular focus on the optimum design of plate and frame heat exchanger and the optimization of electronic packages and stacked packaging of laminar‐convection‐cooled printed circuits.
Originality/value
This paper introduces the entropy generation minimization via controlling the operating parameters and clearly identifies the optimum buoyancy parameter (Gr/Re) at which entropy generation assumes its minimum under different operating conditions.
Details
Keywords
J.J. Hwang, T.Y. Lia and S.H. Chen
Turbulent fluid flow and heat transfer characteristics are analyzed numerically for fluids flowing through a rotating periodical two‐pass square channel. The smooth walls of this…
Abstract
Turbulent fluid flow and heat transfer characteristics are analyzed numerically for fluids flowing through a rotating periodical two‐pass square channel. The smooth walls of this two‐pass channel are subject to a constant heat flux. A two‐equation k‐ε turbulence model with modified terms for Coriolis and rotational buoyancy is employed to resolve this elliptic problem. The duct through‐flow rate and rotating speed are fixed constantly; while the wall heat flux into the fluid is varied to examine the rotating buoyancy effect on the heat transfer and fluid flow characteristics. It is disclosed that the changes in local heat transfer due to the rotational buoyancy in the radially outward flow are more significant than those in the radially inward flow. However, the channel averaged heat transfer is altered slightly due to the rotational buoyancy in the both ducts. Whenever the buoyancy effects are sufficiently strong, the flow reversal appears over the leading face of the radially outward‐flow channel, and the radial distance for initiation of flow separation decreases with increasing the buoyancy parameter. A comparison of the present numerical results with the available experimental data by taking buoyancy into consideration is also presented.
Details
Keywords
Andrew J. Martin, Paul Ginns, Brad Papworth and Harry Nejad
Aboriginal students experience disproportionate academic disadvantage at school. It may be that a capacity to effectively deal with academic setback and challenge (academic…
Abstract
Purpose
Aboriginal students experience disproportionate academic disadvantage at school. It may be that a capacity to effectively deal with academic setback and challenge (academic buoyancy) can reduce the incidence of academic adversity. To the extent that this is the case, academic buoyancy may also be associated with positive educational intentions. This study explores the role of academic buoyancy in Aboriginal students’ post-school educational intentions.
Methodology/approach
The survey-based study comprises Aboriginal (N = 350) and non-Aboriginal (N = 592) high school students in Australia.
Findings
Academic buoyancy yielded larger effect sizes for Aboriginal than non-Aboriginal students’ educational intentions – particularly in senior high school when educational intentions are most likely to translate into post-school educational behaviour.
Social and practical implications
Post-school education is one pathway providing access to social opportunity. Any thorough consideration of students’ passage into and through post-school education must first consider the bases of students’ academic plans and, by implication, their decision to pursue further study. Identifying factors such as academic buoyancy in this process provides some specific direction for practice and policy aimed at optimizing Aboriginal students’ academic and non-academic development.
Originality/value of chapter
Academic buoyancy is a recently proposed construct in the psycho-educational literature and has not been investigated among Aboriginal student populations. Its role in relation to post-school educational intentions is also a novel empirical contribution for both Aboriginal and non-Aboriginal students alike.
Details
Keywords
Youssef Azizi, Brahim Benhamou, Nicolas Galanis and Mohammed El‐Ganaoui
The objective of the present study is to investigate numerically the effects of thermal and buoyancy forces on both upward flow (UF) and downward flow (DF) of air in a vertical…
Abstract
Purpose
The objective of the present study is to investigate numerically the effects of thermal and buoyancy forces on both upward flow (UF) and downward flow (DF) of air in a vertical parallel‐plates channel. The plates are wetted by a thin liquid water film and maintained at a constant temperature lower than that of the air entering the channel.
Design/methodology/approach
The solution of the elliptical PDE modeling the flow field is based on the finite volume method.
Findings
Results show that buoyancy forces have an important effect on heat and mass transfers. Cases with evaporation and condensation have been investigated for both UF and DF. It has been established that the heat transfer associated with these phase changes (i.e. latent heat transfer) may be more or less important compared with sensible heat transfer. The importance of these transfers depends on the temperature and humidity conditions. On the other hand, flow reversal has been predicted for an UF with a relatively high temperature difference between the incoming air and the walls.
Originality/value
Contrary to most studies in channel heat and mass transfer with phase change, the mathematical model considers the full elliptical Navier‐Stokes equations. This allows one to compute situations of flow reversal.
Details
Keywords
Abdelraheem M. Aly and Ehab Mahmoud Mohamed
The purpose of this study is to use an incompressible smoothed particle hydrodynamics (ISPH) method for simulating buoyancy ratio and magnetic field effects on double diffusive…
Abstract
Purpose
The purpose of this study is to use an incompressible smoothed particle hydrodynamics (ISPH) method for simulating buoyancy ratio and magnetic field effects on double diffusive natural convection of a cooper-water nanofluid in a cavity. An open pipe is embedded inside the center of a cavity, and it is occupied by solid particles.
Design/methodology/approach
The dimensionless governing equations in Lagrangian form were solved by ISPH method. Two different thermal conditions were considered for the solid particles. The actions of the solid particles were tracked inside a cavity. The effects of Hartman parameter, Rayleigh number, nanoparticles volume fraction and Lewis number on features of heat and mass transfer and flow field were tested.
Findings
The results showed that the buoyancy ratio changes the directions of the solid particles diffusion in a cavity. The hot solid particles were raised upwards at aiding mode (N > 0) and downwards at an opposing mode (N < 0). A comparison is made with experimental and numerical simulation results, and it showed a well agreement.
Originality/value
Novel studies for the impacts of buoyancy ratio on the diffusion of solid particles embedded in an open pipe during double-diffusive flow were conducted.
Details
Keywords
M.M. Rahman, Sourav Saha, Satyajit Mojumder, Khan Md. Rabbi, Hasnah Hasan and Talaat A. Ibrahim
The purpose of this investigation is to determine the nature of the flow field, temperature distribution and heat and mass transfer in a triangular solar collector enclosure with…
Abstract
Purpose
The purpose of this investigation is to determine the nature of the flow field, temperature distribution and heat and mass transfer in a triangular solar collector enclosure with a corrugated bottom wall in the unsteady condition numerically.
Design/methodology/approach
Non-linear governing partial differential equations (i.e. mass, momentum, energy and concentration equations) are transformed into a system of integral equations by applying the Galerkin weighted residual method. The integration involved in each of these terms is performed using Gauss’ quadrature method. The resulting non-linear algebraic equations are modified by the imposition of boundary conditions. Finally, Newton’s method is used to modify non-linear equations into the linear algebraic equations.
Findings
Both the buoyancy ratio and thermal Rayleigh number play an important role in controlling the mode of heat transfer and mass transfer.
Originality/value
Calculations are performed for various thermal Rayleigh numbers, buoyancy ratios and time periods. For each specific condition, streamline contours, isotherm contours and iso-concentration contours are obtained, and the variation in the overall Nusselt and Sherwood numbers is identified for different parameter combinations.
Details
Keywords
The purpose of this work is to study heat and mass transfer from mixed convection flow of polar fluid along a plate in porous media with chemical reaction.
Abstract
Purpose
The purpose of this work is to study heat and mass transfer from mixed convection flow of polar fluid along a plate in porous media with chemical reaction.
Design/methodology/approach
The governing equations for this problem are solved numerically.
Findings
Polar fluids behave very differently from Newtonian fluids.
Originality/value
This work is original as little work has been reported for polar fluids.
Details
Keywords
M. Naïmi, M. Hasnaoui and J.K. Platten
Analytical and numerical studies are conducted for two‐dimensional steady‐state coupled Marangoni and buoyancy convection of a non‐Newtonian power law fluid confined in a…
Abstract
Analytical and numerical studies are conducted for two‐dimensional steady‐state coupled Marangoni and buoyancy convection of a non‐Newtonian power law fluid confined in a rectangular horizontal shallow cavity subjected to a horizontal temperature gradient between the two short vertical rigid sides, while the upper free surface and the lower rigid one are insulated. The results obtained by combining the two basic mechanisms (thermocapillarity and buoyancy) depend on whether their effects are aiding or opposite. The effect of the non‐Newtonian behavior on the fluid flow, the temperature field, and the heat transfer is studied. The parallel flow is obtained in some particular situations for which a good agreement is observed between the analytical results based on the parallel flow assumption and those corresponding to the numerical simulations.
Details