MHD natural convection flow in cavities filled with square solid blocks

2014 ◽  
Vol 24 (8) ◽  
pp. 1813-1830 ◽  
Author(s):  
Majid Ashouri ◽  
Mohammad Behshad Shafii ◽  
Hossein Rajabi Kokande
Keyword(s):  
Magnetic Field ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Code ◽  
Thermal Conductivity Ratio ◽  
Convection Flow ◽  
Conductivity Ratio ◽  
Natural Convection Flow ◽  
Content Type

Purpose – The purpose of this paper is to study the influence of magnetic field on natural convection inside the enclosures partially filled with conducting square solid obstacles. Also, the effect of thermal conductivity ratio between the solid and fluid materials is investigated for different number of solid blocks. Design/methodology/approach – The dimensionless governing equations are transformed into sets of algebraic equations using finite volume method and momentum equations are solved by the SIMPLE algorithm with the hybrid scheme. The validation of the numerical code was conducted by comparing the results of average Nusselt number with previously published works. Findings – The results indicate that both the magnetic field and solid blocks can significantly affect the flow and temperature fields. It is shown that for a given Rayleigh number, variation of Nusselt number might be increasing or decreasing with change in solid-to-fluid thermal conductivity ratio depending on magnetic field strength and number of solid blocks. Originality/value – No work has been reported previously on the effect of magnetic field on natural convection flow in a cavity partially filled with square solid blocks. The numerical analysis of conductivity ratio between the solid and fluid materials under the effect of magnetic field have been carried out for the first time.

Natural convection flow in a vertical micro-annulus with time-periodic thermal boundary conditions

2018 ◽  
Vol 14 (5) ◽  
pp. 1064-1081
Author(s):  
Basant Kumar Jha ◽  
Michael O. Oni
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Skin Friction ◽  
Convection Flow ◽  
Natural Convection Flow ◽  
Content Type ◽  
Thermal Boundary Conditions ◽  
The Impact ◽  
Time Periodic

PurposeThe purpose of this paper is to investigate the impact of time-periodic thermal boundary conditions on natural convection flow in a vertical micro-annulus.Design/methodology/approachAnalytical solution in terms of Bessel’s function and modified Bessel’s function of order 0 and 1 is obtained for velocity, temperature, Nusselt number, skin friction and mass flow rate.FindingsIt is established that the role of Knudsen number and fluid–wall interaction parameter is to decrease fluid temperature, velocity, Nusselt number and skin friction.Research limitations/implicationsNo laboratory practical or experiment was conducted.Practical implicationsCooling device in electronic panels, card and micro-chips is frequently cooled by natural convection.Originality/valueIn view of the amount of works done on natural convection in microchannel, it becomes interesting to investigate the effect that time-periodic heating has on natural convection flow in a vertical micro-annulus. The purpose of this paper is to examine the impact of time-periodic thermal boundary conditions on natural convection flow in a vertical micro-annulus.

Conjugate heat transfer in porous triangular enclosures with thick bottom wall

2009 ◽  
Vol 19 (5) ◽  
pp. 650-664 ◽  
Author(s):  
Yasin Varol ◽  
Hakan F. Oztop ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Conjugate Heat Transfer ◽  
Bottom Wall ◽  
Thick Wall ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Governing Equations ◽  
Content Type

PurposeThe purpose of this paper is to study the conjugate heat transfer via natural convection and conduction in a triangular enclosure filled with a porous medium.Design/methodology/approachDarcy flow model was used to write governing equations with Boussinesq approximation. The transformed governing equations are solved numerically using a finite difference technique. It is assumed that the enclosure consists of a conducting bottom wall of finite thickness, an adiabatic (insulated) vertical wall and a cooled inclined wall.FindingsFlow patterns, temperature and heat transfer were presented at different dimensionless thickness of the bottom wall, h, from 0.05 to 0.3, different thermal conductivity ratio between solid material and fluid, k, from 0.44 to 283 and Rayleigh numbers, Ra, from 100 to 1000. It is found that both thermal conductivity ratio and thickness of the bottom wall can be used as control parameters for heat transport and flow field.Originality/valueIt is believed that this is the first paper on conduction‐natural convection in porous media filled triangular enclosures with thick wall. In the last years, most of the researchers focused on regular geometries such as rectangular or square cavity bounded by thick wall.

Transient two-dimensional natural convection flow of a nanofluid past an isothermal vertical plate using Buongiorno’s model

2017 ◽  
Vol 27 (1) ◽  
pp. 23-47 ◽  
Author(s):  
Marneni Narahari ◽  
Suresh Kumar Raju Soorapuraju ◽  
Rajashekhar Pendyala ◽  
Ioan Pop
Keyword(s):  
Boundary Layer ◽  
Nusselt Number ◽  
Brownian Motion ◽  
Natural Convection ◽  
Vertical Plate ◽  
Volume Fraction ◽  
Convection Flow ◽  
Nanoparticle Volume Fraction ◽  
Natural Convection Flow ◽  
Content Type

Purpose The purpose of this paper is to present a numerical investigation of the transient two-dimensional natural convective boundary-layer flow of a nanofluid past an isothermal vertical plate by incorporating the effects of Brownian motion and thermophoresis in the mathematical model. Design/methodology/approach The problem is formulated using the Oberbeck–Boussinesq and the standard boundary-layer approximations. The governing coupled non-linear partial differential equations for conservation of mass, momentum, thermal energy and nanoparticle volume fraction have been solved by using an efficient implicit finite-difference scheme of the Crank–Nicolson type, which is stable and convergent. Numerical computations are performed and the results for velocity, temperature and nanoparticle volume fraction are presented in graphs at different values of system parameters such as Brownian motion parameter, thermophoresis parameter, buoyancy ratio parameter, Prandtl number, Lewis number and dimensionless time. The results for local and average skin-friction and Nusselt number are also presented graphically and discussed thoroughly. Findings It is found that the velocity, temperature and nanoparticle volume fraction profiles enhance with respect to time and attain steady-state values as time progresses. The local Nusselt number is found to decrease with increasing thermophoresis parameter, while it increases slightly with increasing Brownian motion parameter. To validate the present numerical results, the steady-state local Nusselt number results for the limiting case of a regular fluid have been compared with the existing well-known results at different Prandtl numbers, and the results are found to be in an excellent agreement. Research limitations/implications The present analysis is limited to the transient laminar natural convection flow of a nanofluid past an isothermal semi-infinite vertical plate in the absence of viscous dissipation and thermal radiation. The unsteady natural convection flow of a nanofluid will be investigated for various physical conditions in a future work. Practical implications Unsteady flow devices offer potential performance improvements as compared with their steady-state counterparts, and the flow fields in the unsteady flow devices are typically transient in nature. The present study provides very useful information for heat transfer engineers to understand the heat transfer enhancement with the nanofluid flows. The present results have immediate relevance in cooling technologies. Originality/value The present research work is relatively original and illustrates the transient nature of the natural convective nanofluid boundary-layer flow in the presence of Brownian motion and thermophoresis.

MHD natural convection flow past an impulsively started infinite vertical porous plate with Newtonian heating in the presence of radiation

2016 ◽  
Vol 26 (6) ◽  
pp. 1932-1953 ◽  
Author(s):  
Marneni Narahari ◽  
M Kamran
Keyword(s):  
Magnetic Field ◽  
Natural Convection ◽  
Thermal Radiation ◽  
Transverse Magnetic Field ◽  
Porous Plate ◽  
Transverse Magnetic ◽  
Convection Flow ◽  
Newtonian Heating ◽  
Natural Convection Flow ◽  
Content Type

Purpose – The purpose of this paper is to investigate the effects of thermal radiation and viscous dissipation on steady natural convection flow of a viscous incompressible fluid along a uniformly moving infinite vertical porous plate with Newtonian heating in the presence of transverse magnetic field. The governing non-linear boundary layer equations are solved by using homotopy analysis method (HAM). The effects of various system parameters on velocity and temperature fields are discussed graphically, and the numerical values for skin friction and Nusselt number are presented in tabular form. Design/methodology/approach – The problem is formulated using the Boussinesq approximation under the effects of thermal radiation and transverse magnetic field. The resulting coupled system of non-linear differential equations is solved using HAM with appropriate boundary conditions for Newtonian heating of the plate. HAM is a powerful method which provides rapidly converging series solution for the velocity and temperature fields. The effects of Prandtl number, Grashof number, suction parameter, magnetic field parameter, radiation parameter and Eckert number on the fluid velocity, temperature, skin friction and Nusselt number have been investigated. Findings – The HAM solution has been successfully applied to find the converging series solution for velocity and temperature fields in terms of pertinent system parameters. Comparison of the exact solution results agree well with the HAM solution results in the absence of Eckert number and this indicates that the HAM solutions are accurate. It is found that the velocity and temperature profiles decreases with the increase of thermal radiation and suction parameters. An increase in the magnetic field parameter leads to a rise in the fluid temperature and fall in the fluid velocity. Research limitations/implications – The present analysis is limited to steady state laminar natural convection flow only. Unsteady natural- /mixed-convection laminar flow in the presence of thermal radiation, chemical reaction and transverse magnetic field will be investigated in a future work. Practical implications – The study provides very useful information for heat transfer engineers to understand the heat transfer rate when the moving vertical porous surface temperature is not known a prior. The present results have immediate relevance in the design of nuclear reactors where vertical moving porous plates are using as control rods. Originality/value – The present research work is relatively original and illustrates the effects of thermal radiation, viscous dissipation and transverse magnetic field on natural convection flow past a uniformly moving infinite vertical porous plate with Newtonian heating.

Thermosolutal natural convection in a partly porous cavity with sinusoidal wall heating and cooling

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Abdeslam Omara ◽  
Mouna Touiker ◽  
Abderrahim Bourouis
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Clear Fluid ◽  
Content Type ◽  
Heating And Cooling ◽  
Fortran Code ◽  
Double Diffusive ◽  
Sinusoidal Wall

Purpose This paper aims to consider numerical analysis of laminar double-diffusive natural convection inside a non-homogeneous closed medium composed of a saturated porous matrix and a clear binary fluid under spatial sinusoidal heating/cooling on one side wall and uniform salting. Design/methodology/approach The domain of interest is a partially square porous enclosure with sinusoidal wall heating and cooling. The fluid flow, heat and mass transfer dimensionless governing equations associated with the corresponding boundary conditions are discretized using the finite volume method. The resulting algebraic equations are solved by an in-house FORTRAN code and the SIMPLE algorithm to handle the non-linear character of conservation equations. The validity of the in-house FORTRAN code is checked by comparing the current results with previously published experimental and numerical works. The effect of the porous layer thickness, the spatial frequency of heating and cooling, the Darcy number, the Rayleigh number and the porous to fluid thermal conductivity ratio is analyzed. Findings The results demonstrate that for high values of the spatial frequency of heating and cooling (f = 7), temperature contours show periodic variations with positive and negative values providing higher temperature gradient near the thermally active wall. In this case, the temperature variation is mainly in the porous layer, while the temperature of the clear fluid region is practically the same as that imposed on the left vertical wall. This aspect can have a beneficial impact on thermal insulation. Besides, the porous to fluid thermal conductivity ratio, Rk, has practically no effect on Shhot wall, contrary to Nuinterface where a strong increase is observed as Rk is increased from 0.1 to 100, and much heat transfer from the hot wall to the clear fluid via the porous media is obtained. Practical implications The findings are useful for devices working on double-diffusive natural convection inside non-homogenous cavities. Originality/value The authors believe that the presented results are original and have not been published elsewhere.

A Numerical Study of Conjugate Heat Transfer by Natural Convection and Surface Radiation in a Square Enclosure With Thick Adiabatic Walls

2013 ◽  
Author(s):  
H. Hadim ◽  
K. Blecker
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Natural Convection ◽  
Average Nusselt Number ◽  
Surface Radiation ◽  
Thick Wall ◽  
Thermal Conductivity Ratio ◽  
Conductivity Ratio ◽  
Square Enclosure

A numerical solution of heat transfer by combined natural convection and surface radiation in a square enclosure with thick adiabatic top and bottom walls and isothermal vertical walls is presented. The present model was used to obtain new results with the addition of thermal conduction at the thick top and bottom walls for a thermal conductivity ratio, K = ksolid/kfluid, that ranges from 0 to 10, emissivity of the adiabatic walls that ranges from 0 to 1, and the Rayleigh Number that ranges from 103 to 106. The model was validated by comparing the results to a benchmark solution and other solutions found in the literature. The results showed that with an increase in thermal conductivity ratio, the flow circulation decreases while the average Nusselt Number increases indicating increased heat transfer across the thick walls and the fluid in the corners. The results indicate that while past studies have shown negligible impact of the emissivity of the adiabatic walls on characteristics of the flow and heat transfer within the cavity, when a wall with moderate heat capacity and conductivity is considered, the resulting flow velocity and temperature distribution within the cavity are found to be significantly influenced by the thick wall emissivity. As the conductivity ratio increases this discrepancy between thin and thick walls becomes greater, there is further need for a more complex and accurate model including the thick walls. The results also showed that an increase in the emissivity of the adiabatic walls results in a slight decrease in the average Nusselt Number.

Entropy generation analysis during MHD natural convection flow of hybrid nanofluid in a square cavity containing a corrugated conducting block

2019 ◽  
Vol 30 (3) ◽  
pp. 1115-1136 ◽  
Author(s):  
Tahar Tayebi ◽  
Ali J. Chamkha
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Thermal Conductivity ◽  
Entropy Generation ◽  
Thermal Conductivity Ratio ◽  
Hybrid Nanofluid ◽  
Conductivity Ratio ◽  
Square Cavity ◽  
Content Type ◽  
Solid Block

Purpose The purpose of this paper is to study the influence of magnetic field on entropy generation and natural convection inside an enclosure filled with a hybrid nanofluid and having a conducting wavy solid block. Also, the effect of fluid–solid thermal conductivity ratio is investigated. Design/methodology/approach The governing equations that are formulated in the dimensionless form are discretized via finite volume method. The velocity–pressure coupling is assured by the SIMPLE algorithm. Heat transfer balance is used to verify the convergence. The validation of the numerical results was performed by comparing qualitatively and quantitatively the results with previously published investigations. Findings The results indicate that the magnetic field and the conductivity ratio of the wavy solid block can significantly affect the dynamic and thermal field and, consequently, the heat transfer rate and entropy generation because of heat transfer, fluid friction and magnetic force. Originality/value To the best of the authors’ knowledge, the present numerical study is the first attempt to use hybrid nanofluid for studying the entropy generation because of magnetohydrodynamic natural convective flow in a square cavity with the presence of a wavy circular conductive cylinder. Irreversibilities due to magnetic effect are taken into account. The effect of fluid–solid thermal conductivity ratio is considered.

Magnetohydrodynamic time-dependent computational natural convection flow, heat and mass transfer in inclined semi-circular enclosures

2016 ◽  
Vol 26 (8) ◽  
pp. 2310-2330 ◽  
Author(s):  
M.M. Rahman ◽  
Hakan F. Öztop ◽  
R. Saidur ◽  
A.G. Naim ◽  
Khaled S. Al-Salem ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Mass Transfer ◽  
Natural Convection ◽  
Heat And Mass Transfer ◽  
Inclination Angle ◽  
Time Dependent ◽  
Convection Flow ◽  
Natural Convection Flow ◽  
Content Type ◽  
Flow Heat

Purpose The purpose of this paper is to make a numerical analysis on unsteady analysis of natural convection heat and mass transfer to obtain flow field, temperature distribution, and concentration distribution. Design/methodology/approach A finite element method is applied to solve governing equations of natural convection in curvilinear-shaped system for different parameters as thermal Rayleigh numbers (103=RaT=106), inclination angle (0°=φ=60°) and Hartmann numbers (0=Ha=100). Findings Both magnetic field and inclination angle can be used as control parameter on heat and mass transfer. Flow strength decreases almost 100 percent between Ha=0 and Ha=100 on behalf of the higher values of thermal Rayleigh number. Originality/value The originality of this work is to application of magnetic field on time-dependent natural convection flow, heat and mass transfer for curvilinear geometry.

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