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1 – 8 of 8Taher Armaghani, A. Kasaeipoor, Mohsen Izadi and Ioan Pop
The purpose of this paper is to numerically study MHD natural convection and entropy generation of Al2O3-water alumina nanofluid inside of T-shaped baffled cavity which is…
Abstract
Purpose
The purpose of this paper is to numerically study MHD natural convection and entropy generation of Al2O3-water alumina nanofluid inside of T-shaped baffled cavity which is subjected to a magnetic field.
Design/methodology/approach
Effect of various geometrical, fluid and flow factors such as aspect ratio of enclosure and baffle length, Rayleigh and Hartmann number of nanofluid have been considered in detail. The hydrodynamics and thermal indexes of nanofluid have been described using streamlines, isotherms and isentropic lines.
Findings
It is found that by enhancing Hartmann number, symmetrical streamlines gradually lose symmetry and their values decline. It is found that by enhancing Hartmann number, symmetrical streamlines gradually lose symmetry and their values decline. The interesting finding is an increase in the impact of Hartmann number on heat transfer indexes with augmenting Rayleigh number. However, with augmenting Rayleigh number and, thus, strengthening the buoyant forces, the efficacy of Hartmann number one, an index indicating the simultaneous impact of natural heat transfer to entropy generation increases. It is clearly seen that the efficacy of nanofluid on increased Nusselt number enhances with increasing aspect ratio of the enclosure. Based on the results, the Nusselt number generally enhances with the larger baffle length in the enclosure. Finally, with larger Hartmann number and lesser Nusselt one, entropy production is reduced.
Originality/value
The authors believe that all the results, both numerical and asymptotic, are original and have not been published elsewhere.
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Taher Armaghani, A.M. Rashad, Omid Vahidifar, S.R. Mishra and A.J. Chamkha
This paper aims to concentrate on the impacts of a discrete heat source location on heat transfer and entropy generation for a Ag-water nanofluid in an open inclined L-shaped…
Abstract
Purpose
This paper aims to concentrate on the impacts of a discrete heat source location on heat transfer and entropy generation for a Ag-water nanofluid in an open inclined L-shaped cavity.
Design/methodology/approach
The governing partial differential equations for this study are computed by the finite volume method.
Findings
The results show that increasing the inclination angle leads to a rise in heat transfer. It is clear with the increase in the nanoparticles volume fraction that the thermal performance reduces, and it increases when the inclination angle increases.
Originality/value
Because of the continuous literature survey, the authors have not found a study that concentrates on the entropy generation in a wide variety of irregular ducts. Thus, in this paper, they present the analysis of entropy generation in an L-shaped duct experiencing a mixed convective flow with a nanofluid. The authors deal with this geometry because it is very useful in cooling systems of nuclear and chemical reactors and electronic components.
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Kasra Ayoubi Ayoubloo, Mohammad Ghalambaz, Taher Armaghani, Aminreza Noghrehabadi and Ali J. Chamkha
This paper aims to theoritically investigate the free convection flow and heat transfer of a non-Newtonian fluid with pseudoplastic behavior in a cylindrical vertical cavity…
Abstract
Purpose
This paper aims to theoritically investigate the free convection flow and heat transfer of a non-Newtonian fluid with pseudoplastic behavior in a cylindrical vertical cavity partially filled with a layer of a porous medium.
Design/methodology/approach
The non-Newtonian behavior of the pseudoplastic liquid is described by using a power-law non-Newtonian model. There is a temperature difference between the internal and external cylinders. The porous layer is attached to the internal cylinder and has a thickness of D. Upper and lower walls of the cavity are well insulated. The governing equations are transformed into a non-dimensional form to generalize the solution. The finite element method is used to solve the governing equations numerically. The results are compared with the literature results in several cases and found in good agreement.
Findings
The influence of the thickness of the porous layer, Rayleigh number and non-Newtonian index on the heat transfer behavior of a non-Newtonian pseudoplastic fluid is addressed. The increase of pseudoplastic behavior and increase of the thickness of the porous layer enhances the heat transfer. By increase of the porous layer from 0.6 to 0.8, the average Nusselt number increased from 0.15 to 0.25. The increase of non-Newtonian effects (decrease of the non-Newtonian power-law index) enhances the heat transfer rate.
Originality/value
The free convection behavior of a pseudoplastic-non-Newtonian fluid in a cylindrical enclosure partially filled by a layer of a porous medium is addressed for the first time.
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Ammar I. Alsabery, Taher Armaghani, Ali J. Chamkha, Muhammad Adil Sadiq and Ishak Hashim
The aim of this study is to investigate the effects of two-phase nanofluid model on mixed convection in a double lid-driven square cavity in the presence of a magnetic field. The…
Abstract
Purpose
The aim of this study is to investigate the effects of two-phase nanofluid model on mixed convection in a double lid-driven square cavity in the presence of a magnetic field. The authors believe that this work is a good contribution for improving the thermal performance and the heat transfer enhancement in some engineering instruments.
Design/methodology/approach
The current work investigates the problem of mixed convection heat transfer in a double lid-driven square cavity in the presence of magnetic field. The used cavity is filled with water-Al2O3 nanofluid based on Buongiorno’s two-phase model. The bottom horizontal wall is maintained at a constant high temperature and moves to the left/right, while the top horizontal wall is maintained at a constant low temperature and moves to the right/left. The left and right vertical walls are thermally insulated. The dimensionless governing equations are solved numerically using the Galerkin weighted residual finite element method.
Findings
The obtained results show that the heat transfer rate enhances with an increment of Reynolds number or a reduction of Hartmann number. In addition, effects of thermophoresis and Brownian motion play a significant role in the growth of convection heat transfer.
Originality/value
According to above-mentioned studies and to the authors’ best knowledge, there has no study reported the MHD mixed convection heat transfer in a double lid-driven cavity using the two-phase nanofluid model. Thus, the authors of the present study believe that this work is valuable. Therefore, the aim of this comprehensive numerical study is to investigate the effects of two-phase nanofluid model on mixed convection in a double lid-driven square cavity in the presence of a magnetic field. The authors believe that this work is a good contribution for improving the thermal performance and the heat transfer enhancement in some engineering instruments.
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Ahad Abedini, Saeed Emadoddin and Taher Armaghani
This study aims to investigate the numerical analysis of mixed convection within the horizontal annulus in the presence of water-based fluid with nanoparticles of aluminum oxide…
Abstract
Purpose
This study aims to investigate the numerical analysis of mixed convection within the horizontal annulus in the presence of water-based fluid with nanoparticles of aluminum oxide, copper, silver and titanium oxide. Numerical solution is performed using a finite-volume method based on the SIMPLE algorithm, and the discretization of the equations is generally of the second order. Inner and outer cylinders have a constant temperature, and the inner cylinder temperature is higher than the outer one. The two cylinders can be rotated in both directions at a constant angular velocity. The effect of parameters such as Rayleigh, Richardson, Reynolds and the volume fraction of nanoparticles on heat transfer and flow pattern are investigated. The results show that the heat transfer rate increases with the increase of the Rayleigh number, as well as by increasing the volume fraction of the nanoparticles, the heat transfer rate increases, and this increase is about 8.25 per cent for 5 per cent volumetric fraction. Rotation of the cylinders reduces the overall heat transfer. Different directions of rotation have a great influence on the flow pattern and isotherms, and ultimately on heat transfer. The addition of nanoparticles does not have much effect on the flow pattern and isotherms, but it is quantitatively effective. The extracted results are in good agreement with previous works.
Design/methodology/approach
Studying mixed convection heat transfer in the horizontal annulus in the presence of a water-based fluid with aluminum oxide, copper, silver and titanium oxide nanoparticles is carried out quantitatively using a finite-volume method based on the SIMPLE algorithm.
Findings
Increasing the Rayleigh number increases the Nusselt number. Increasing the Richardson number increases heat transfer. Adding nanoparticles does not have much effect on the flow pattern but is effective quantitatively on heat transfer parameters. The addition of nanoparticles sometimes increases the heat transfer rate by about 8.25 per cent. In constant Rayleigh numbers, increasing the Reynolds number reduces heat transfer. The Rayleigh and Reynolds numbers greatly affect the isotherms and streamlines. In addition to the thermal conductivity of nanoparticles, the thermo-physical properties of nanoparticles has great effect in the formation of isotherms and streamlines and ultimately heat transfer.
Originality/value
Studying the effect of different direction of rotation on the isotherms and streamlines, as well as the comparison of different nanoparticles on mixed convection heat transfer in annulus.
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Alireza Rahimi, Ali Dehghan Saee, Abbas Kasaeipoor and Emad Hasani Malekshah
The purpose of this paper is to carry out a comprehensive review of some latest studies devoted to natural convection phenomenon in the enclosures because of its significant…
Abstract
Purpose
The purpose of this paper is to carry out a comprehensive review of some latest studies devoted to natural convection phenomenon in the enclosures because of its significant industrial applications.
Design/methodology/approach
Geometries of the enclosures have considerable influences on the heat transfer which will be important in energy consumption. The most useful geometries in engineering fields are treated in this literature, and their effects on the fluid flow and heat transfer are presented.
Findings
A great variety of geometries included with different physical and thermal boundary conditions, heat sources and fluid/nanofluid media are analyzed. Moreover, the results of different types of methods including experimental, analytical and numerical are obtained. Different natures of natural convection phenomenon including laminar, steady-state and transient, turbulent are covered. Overall, the present review enhances the insight of researchers into choosing the best geometry for thermal process.
Originality/value
A comprehensive review on the most practical geometries in the industrial application is performed.
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HamidReza KhakRah, Mehdi Mohammaei, Payam Hooshmand, Navid Bagheri and Emad Hasani Malekshah
The nanofluid flow and heat transfer within a heat exchanger, with different thermal arrangements of internal active bodies, are investigated.
Abstract
Purpose
The nanofluid flow and heat transfer within a heat exchanger, with different thermal arrangements of internal active bodies, are investigated.
Design/methodology/approach
For the numerical simulations, the lattice Boltzmann method is utilized. The KKL model is used to predict the dynamic viscosity of CuO-water nanofluid. Furthermore, the Brownian method is taken account using this model. The influence of shapes of nanoparticles on the heat transfer performance is considered.
Findings
The results show that the platelet nanoparticles render higher average Nusselt number showing better heat transfer performance. In order to perform comprehensive analysis, the heatline visualization, local and total entropy generation, local and average Nusselt variation are employed.
Originality/value
The originality of this work is carrying out a comprehensive investigation of nanofluid flow and heat transfer during natural convection using lattice Boltzmann method and employing second law analysis and heatline visualization.
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