M. Sathiyamoorthy and Ali J. Chamkha
– The purpose of this paper is to optimize the heat transfer rate in square cavity by attaching fin at the bottom wall.
Abstract
Purpose
The purpose of this paper is to optimize the heat transfer rate in square cavity by attaching fin at the bottom wall.
Design/methodology/approach
The problem is formulated and solved using finite element method. Accuracy of the method is validated by comparisons with previously published work.
Findings
It was found that attaching fin reduces heat transfer rate in the cavity.
Originality/value
Although the problem is not very original it is important in that many applications have heating on adjacent walls.
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M. Sathiyamoorthy and Ali J. Chamkha
The purpose of this paper is to study the effect of magnetic field on natural convection in an enclosure with uniformly or linearly heated adjacent walls and especially its effect…
Abstract
Purpose
The purpose of this paper is to study the effect of magnetic field on natural convection in an enclosure with uniformly or linearly heated adjacent walls and especially its effect on the local and average Nusselt numbers.
Design/methodology/approach
The problem is formulated and solved using the finite element method. Accuracy of the method is validated by comparisons with previously published work.
Findings
It was found that the presence of a magnetic filed causes significant effects on the local and average Nusselt numbers on all considered walls.
Originality/value
Although the problem is not very original it is important in that many applications have heating on adjacent walls.
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Mohammad Ghalambaz, Mahmoud Sabour, Ioan Pop and Dongsheng Wen
The present study aims to address the flow and heat transfer of MgO-MWCNTs/EG hybrid nanofluid in a complex shape enclosure filled with a porous medium. The enclosure is subject…
Abstract
Purpose
The present study aims to address the flow and heat transfer of MgO-MWCNTs/EG hybrid nanofluid in a complex shape enclosure filled with a porous medium. The enclosure is subject to a uniform inclined magnetic field and radiation effects. The effect of the presence of a variable magnetic field on the natural convection heat transfer of hybrid nanofluids in a complex shape cavity is studied for the first time. The geometry of the cavity is an annular space with an isothermal wavy outer cold wall. Two types of the porous medium, glass ball and aluminum metal foam, are adopted for the porous space. The governing equations for mass, momentum and heat transfer of the hybrid nanofluid are introduced and transformed into non-dimensional form. The actual available thermal conductivity and dynamic viscosity data for the hybrid nanofluid are directly used for thermophysical properties of the hybrid nanofluid.
Design/methodology/approach
The governing equations for mass, momentum and heat transfer of hybrid nanofluid are introduced and transformed into non-dimensional form. The thermal conductivity and dynamic viscosity of the nanofluid are directly used from the experimental results available in the literature. The finite element method is used to solve the governing equations. Grid check procedure and validations were performed.
Findings
The effect of Hartmann number, Rayleigh number, Darcy number, the shape of the cavity and the type of porous medium on the thermal performance of the cavity are studied. The outcomes show that using the composite nanoparticles boosts the convective heat transfer. However, the rise of the volume fraction of nanoparticles would reduce the overall enhancement. Considering a convective dominant regime of natural convection flow with Rayleigh number of 107, the maximum enhancement ratio (Nusselt number ratio compared to the pure fluid) for the case of glass ball is about 1.17 and for the case of aluminum metal foam is about 1.15 when the volume fraction of hybrid nanoparticles is minimum as 0.2 per cent.
Originality/value
The effect of the presence of a variable magnetic field on the natural convection heat transfer of a new type of hybrid nanofluids, MgO-MWCNTs/EG, in a complex shape cavity is studied for the first time. The results of this paper are new and original with many practical applications of hybrid nanofluids in the modern industry.
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Behnam Rafiei, Hamed Masoumi, Mohammad Saeid Aghighi and Amine Ammar
The purpose of this paper is to analyze the effects of complex boundary conditions on natural convection of a yield stress fluid in a square enclosure heated from below (uniformly…
Abstract
Purpose
The purpose of this paper is to analyze the effects of complex boundary conditions on natural convection of a yield stress fluid in a square enclosure heated from below (uniformly and non-uniformly) and symmetrically cooled from the sides.
Design/methodology/approach
The governing equations are solved numerically subject to continuous and discontinuous Dirichlet boundary conditions by Galerkin’s weighted residuals scheme of finite element method and using a non-uniform unstructured triangular grid.
Findings
Results show that the overall heat transfer from the heated wall decreases in the case of non-uniform heating for both Newtonian and yield stress fluids. It is found that the effect of yield stress on heat transfer is almost similar in both uniform and non-uniform heating cases. The yield stress has a stabilizing effect, reducing the convection intensity in both cases. Above a certain value of yield number Y, heat transfer is only due to conduction. It is found that a transition of different modes of stability may occur as Rayleigh number changes; this fact gives rise to a discontinuity in the variation of critical yield number.
Originality/value
Besides the new numerical method based on the finite element and using a non-uniform unstructured grid for analyzing natural convection of viscoplastic materials with complex boundary conditions, the originality of the present work concerns the treatment of the yield stress fluids under the influence of complex boundary conditions.
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GholamReza Kefayati, Mofid Gorji, Hasan Sajjadi and Davood Domiri Ganji
Magneto hydrodynamic (MHD) flows in fluids is known to have an important effect on heat transfer and fluid flow in various substances while the quality of the substances and the…
Abstract
Purpose
Magneto hydrodynamic (MHD) flows in fluids is known to have an important effect on heat transfer and fluid flow in various substances while the quality of the substances and the considered shapes can influence the amount of changes. Thus, MHD flows in a different form and widespread alterations in the kind of the material and the power of MHD flow were carried out by lattice Boltzmann method (LBM) in this investigation. The aim of this paper is to identify the ability of LBM for solving MHD flows as the effect of different substances in the presence of the magnetic field changes.
Design/methodology/approach
This method was utilized for solving MHD natural convection in an open cavity while Hartmann number varies from 0 to 150 and Rayleigh number is considered at values of Ra=103, 104 and 105, with the Prandtl number altering in a wide range of Pr=0.025, 0.71 and 6.2. An appropriate validation with previous numerical investigations demonstrated that this attitude is a suitable method for MHD problems.
Findings
Results show the alterations of Prandtl numbers influence the isotherms and the streamlines widely at different Rayleigh and Hartmann numbers simultaneously. Moreover, heat transfer declines with the increment of Hartmann number, while this reduction is marginal for Ra=103 by comparison with other Rayleigh numbers. The effect of the magnetic field on the average Nusselt number at Liquid Gallium (Pr=0.025) is the least among considered materials.
Originality/value
In this method, just the force term at LBM changes in the presence of MHD flow as the added term rises from the classic equations of fluids mechanic. Moreover, all parameters of the added term and the method of their computing are exhibited.
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M. Sabour, Mohammad Ghalambaz and Ali Chamkha
The purpose of this study is to theoretically analyze the laminar free convection heat transfer of nanofluids in a square cavity. The sidewalls of the cavity are subject to…
Abstract
Purpose
The purpose of this study is to theoretically analyze the laminar free convection heat transfer of nanofluids in a square cavity. The sidewalls of the cavity are subject to temperature difference, whereas the bottom and top are insulated. Based on the available experimental results in the literature, two new non-dimensional parameters, namely, the thermal conductivity parameter (Nc) and dynamic viscosity parameter (Nv) are introduced. These parameters indicate the augmentation of the thermal conductivity and dynamic viscosity of the nanofluid by dispersing nanoparticles.
Design/methodology/approach
The governing equations are transformed into non-dimensional form using the thermo-physical properties of the base fluid. The obtained governing equations are solved numerically using the finite element method. The results are reported for the general non-dimensional form of the problem as well as case studies in the form of isotherms, streamlines and the graphs of the average Nusselt number. Using the concept of Nc and Nv, some criteria for convective enhancement of nanofluids are proposed. As practical cases, the effect of the size of nanoparticles, the shape of nanoparticles, the type of nanoparticles, the type of base fluids and working temperature on the enhancement of heat transfer are analyzed.
Findings
The results show that the increase of the magnitude of the Rayleigh number increases of the efficiency of using nanofluids. The type of nanoparticles and the type of the base fluid significantly affects the enhancement of using nanofluids. Some practical cases are found, in which utilizing nanoparticles in the base fluid results in deterioration of the heat transfer. The working temperature of the nanofluid is very crucial issue. The increase of the working temperature of the nanofluid decreases the convective heat transfer, which limits the capability of nanofluids in decreasing the size of the thermal systems.
Originality/value
In the present study, a separation line based on two non-dimensional parameters (i.e. Nc and Nv) are introduced. The separation line demonstrates a boundary between augmentation and deterioration of heat transfer by using nanoparticles. Indeed, by utilizing the separation lines, the convective enhancement of using nanofluid with a specified Nc and Nv can be simply estimated.
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Harun Zontul, Hudhaifa Hamzah and Besir Sahin
This paper aims to exhibit a numerical study to analyze the influence of a periodic magnetic source on free convection flow and entropy generation of a ferrofluid in a baffled…
Abstract
Purpose
This paper aims to exhibit a numerical study to analyze the influence of a periodic magnetic source on free convection flow and entropy generation of a ferrofluid in a baffled cavity. In this study, ferrofluid nanofluid was selected due to its ability to image magnetic domain structures within the cavity. The non-uniform magnetic source is considered as a sinusoidal distribution in the vertical direction.
Design/methodology/approach
The finite volume technique is used to evaluate the steady two-dimensional partial differential equations that govern the flow with its corresponding boundary conditions.
Findings
The obtained results indicate that a significant increase in the average Nusselt number can be achieved with the use of the periodic magnetic source instead of a uniform case. In addition, the effectiveness of the adiabatic baffle notably depends on its position and Rayleigh number. Regardless of the values of period and Hartmann numbers, the periodic magnetic source has a higher entropy generation and lower Bejan number than the uniform magnetic source.
Originality/value
The novelty of this research lies in applying a periodic magnetic source on the natural convection of ferrofluids in a baffled cavity.
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M. Muthtamilselvan, K. Periyadurai and Deog Hee Doh
The main purpose of this study is to investigate the natural convection of micropolar fluid in a square cavity with two orthogonal heaters placed inside. The study of natural…
Abstract
Purpose
The main purpose of this study is to investigate the natural convection of micropolar fluid in a square cavity with two orthogonal heaters placed inside. The study of natural convection in a two-dimensional enclosure determines the effect of non-uniform heated plate on certain micropolar fluid flows which are found in many engineering applications. Therefore, because of its practical interest in the engineering fields such as building design, cooling of electronic components, melting and solidification process, solar energy systems, solar collectors, liquid crystals, animal blood, colloidal fluids and polymeric fluids, the topic needs to be further explored.
Design/methodology/approach
The dimensionless governing equations have been solved by finite volume method of the second-order central difference and upwind scheme.
Findings
The effects of the Rayleigh number, nonuniformity parameter and vortex viscosity parameter on fluid flow and heat transfer have been analyzed. The rate of heat transfer increases with an increase in the aspect ratio of the heated plates for all the values of Rayleigh number and vortex viscosity parameter. The heat transfer rate is reduced with an increase in the vortex viscosity parameter. It is predicted that the non-uniform of the baffle gives better heat transfer than uniform heating.
Originality/value
The present numerical results were tested against the experimental work. The present results have an excellent agreement with the results obtained by the previous experimental work.
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Modeling of multi-phase flows for Rayleigh-Taylor instability and natural convection in a square cavity has been investigated using an incompressible smoothed particle…
Abstract
Purpose
Modeling of multi-phase flows for Rayleigh-Taylor instability and natural convection in a square cavity has been investigated using an incompressible smoothed particle hydrodynamics (ISPH) technique. In this technique, incompressibility is enforced by using SPH projection method and a stabilized incompressible SPH method by relaxing the density invariance condition is applied. The paper aims to discuss these issues.
Design/methodology/approach
The Rayleigh-Taylor instability is introduced in two and three phases by using ISPH method. The author simulated natural convection in a square/cubic cavity using ISPH method in two and three dimensions. The solutions represented in temperature, vertical velocity and horizontal velocity have been studied with different values of Rayleigh number Ra parameter (103=Ra=105). In addition, characteristic based scheme in Finite Element Method is introduced for modeling the natural convection in a square cavity.
Findings
The results for Rayleigh-Taylor instability and natural convection flow had been compared with the previous researches.
Originality/value
Modeling of multi-phase flows for Rayleigh-Taylor instability and natural convection in a square cavity has been investigated using an ISPH technique. In ISPH method, incompressibility is enforced by using SPH projection method and a stabilized incompressible SPH method by relaxing the density invariance condition is introduced. The Rayleigh-Taylor instability is introduced in two and three phases by using ISPH method. The author simulated natural convection in a square/cubic cavity using ISPH method in two and three dimensions.
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Rangaswamy Navamani and Nadarajan Murugan
The purpose of this paper is to numerically study transient natural convective flow in a square cavity with partially heated and cooled vertical walls, thermally insulated top…
Abstract
Purpose
The purpose of this paper is to numerically study transient natural convective flow in a square cavity with partially heated and cooled vertical walls, thermally insulated top wall and linearly heated bottom wall.
Design/methodology/approach
The governing equations of motion are non‐dimensionalized and reformulated using stream function‐vorticity approach. Alternating direction implicit finite difference scheme is used to solve the coupled equations.
Findings
The transient results obtained for different values of Grashof number (Gr) and fixed Prandtl number Pr = 0.733 are presented in the form of isotherms, streamlines, bifurcation diagram and time series. The transition from steady to oscillatory motions is analyzed in detail with respect to Gr. The flow is observed to be steady up to Gr ≈ 2 × 104. A time‐periodic unsteady solution first appears at Gr = 20,900 and the amplitude of the fluctuation grows as Gr is increased.
Research limitations/implications
The study is limited to laminar flow in a square cavity. Further extension of this work could include the influence of various choices of Prandtl number and the effect of aspect ratio. Buoyancy‐driven convection in a sealed cavity with differentially heated walls is a prototype of many industrial applications such as energy‐efficient design of buildings and rooms, convective heat transfer associated with boilers, etc.
Originality/value
The paper presents an original computer program written in FORTRAN to solve the partial differential equations.