scholarly journals Entropy production and mixed convection within trapezoidal cavity having nanofluids and localised solid cylinder

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Muhamad S. Ishak ◽  
Ammar I. Alsabery ◽  
Ishak Hashim ◽  
Ali J. Chamkha
Keyword(s):  
Mixed Convection ◽  
Entropy Production ◽  
Volume Fraction ◽  
Boussinesq Approximation ◽  
Horizontal Surface ◽  
Bejan Number ◽  
Solid Cylinder ◽  
Significant Control ◽  
Nusselt Numbers ◽  
Element Technique

AbstractThe entropy production and mixed convection within a trapezoidal nanofluid-filled cavity having a localised solid cylinder is numerically examined using the finite element technique. The top horizontal surface moving at a uniform velocity is kept at a cold temperature, while the bottom horizontal surface is thermally activated. The remaining surfaces are maintained adiabatic. Water-based nanofluids ($$\text {Al}_2\text {O}_3$$ Al 2 O 3 nanoparticles) are used in this study, and the Boussinesq approximation applies. The influence of the Reynolds number, Richardson number, nanoparticles volume fraction, dimensionless radius and location of the solid cylinder on the streamlines, isotherms and isentropic are examined. The results show that the solid cylinder’s size and location are significant control parameters for optimising the heat transfer and the Bejan number inside the trapezoidal cavity. Furthermore, the maximum average Nusselt numbers are obtained for high R values, where the average Nusselt number is increased by 30% when R is raised from 0 to 0.25.

Numerical Study on Mixed Convection and Entropy Generation of a Nanofluid in a Lid-Driven Square Enclosure

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
R. K. Nayak ◽  
S. Bhattacharyya ◽  
I. Pop
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Entropy Generation ◽  
Volume Fraction ◽  
Numerical Study ◽  
Control Volume ◽  
Transport Equations ◽  
Bejan Number ◽  
Square Enclosure ◽  
Wide Range

A numerical investigation of mixed convection due to a copper–water nanofluid in an enclosure is presented. The mixed convection is governed by moving the upper lid of the enclosure and imposing a vertical temperature gradient. The transport equations for fluid and heat are modeled by using the Boussinesq approximation. A modified form of the control volume based SIMPLET algorithm is used for the solution of the transport equations. The fluid flow and heat transfer characteristics are studied for a wide range of Reynolds number and Grashof number so as to have the Richardson number greater or less than 1. The nanoparticle volume fraction is considered up to 20%. Heat flow patterns are analyzed through the energy flux vector. The rate of enhancement in heat transfer due to the addition of nanoparticles is analyzed. The entropy generation and Bejan number are evaluated to demonstrate the thermodynamic optimization of the mixed convection. We have obtained the enhancement rate in heat transfer and entropy generation in nanofluid for a wide range of parameter values.

Nonhomogeneous Model for the Mixed Convection and Entropy Generation of a Nanofluid in a Lid-Driven Inclined Enclosure With Discrete Heat Source

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
S. Dutta ◽  
S. Bhattacharyya ◽  
I. Pop
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Entropy Generation ◽  
Inclination Angle ◽  
Volume Fraction ◽  
Numerical Study ◽  
Homogeneous Model ◽  
Staggered Grid ◽  
Brownian Diffusion ◽  
Bejan Number

Abstract A numerical study on the mixed convection of Al2O3–water nanofluid in a lid-driven inclined square enclosure partially heated from below is performed based on Buongiorno's two phase model. The velocity of the nanoparticles relative to the base fluid is considered due to thermophoresis and Brownian diffusion. The thermophysical properties of the nanofluid are assumed to be dependent on temperature as well as the nanoparticle volume fraction. A control volume method over a staggered grid arrangement is used to discretize the governing equations. The discretized equations of two-dimensional continuity, momentum, energy, and volume fraction are solved through a pressure-correction-based semi-implicit method for pressure linked equations (SIMPLE) algorithm. The effects of relevant parameters such as nanoparticle diameter (25 nm ≤ dp ≤ 90 nm), Richardson number (0.1≤Ri≤5), nanoparticle bulk volume fraction (0 ≤φb≤ 0.05) on the mixed convection of the nanofluid is studied by considering the inclination angle of the enclosure to vary between 0 deg and 60 deg. The entropy generation as well as the Bejan number is evaluated to illustrate the thermodynamic optimization of the mixed convection. Both the heat transfer and entropy generation are higher in the nanofluid compared to the clear fluid and the rate of increment in entropy generation remains lower than the rate by which the heat transfer is augmented in the nanofluid. We find that due to the presence of the Brownian diffusion and thermophoresis in the nonhomogeneous model, a higher heat transfer is yielded as compared to the homogeneous model. The discrepancy between the homogeneous and nonhomogeneous models is significant when the mixed convection is dominated by the shear force. When the mixed convection is dominated by the thermal buoyancy, an increase in positive inclination angle of the enclosure creates a significant increment in the heat transfer.

scholarly journals Entropy generation due to the mixed convection flow of MWCNT−MgO/water hybrid nanofluid in a vented complex shape cavity

2020 ◽  
Vol 307 ◽  
pp. 01007
Author(s):  
Mahdi Benzema ◽  
Youb Khaled Benkahla ◽  
Ahlem Boudiaf ◽  
Seif-Eddine Ouyahia ◽  
Mohammed El Ganaoui
Keyword(s):  
Mixed Convection ◽  
Entropy Generation ◽  
Complex Shape ◽  
Volume Fraction ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Convection Flow ◽  
Hybrid Nanofluid ◽  
Bejan Number ◽  
Inclined Plate

This paper reports a numerical study of mixed convection heat transfer with entropy generation in a vented complex shape cavity filled with MWCNT−MgO (15:85 vol %) /water hybrid nanofluid. A hot source is placed at the mid potion of the inclined plate of the enclosure, while the rest of the rigid walls are adiabatic. A thermo-dependent correlations proposed by [12] for the dynamic viscosity and the thermal conductivity, especially developed for the considered fluid, are used. After validation of the model, the analysis has been done for a Reynolds numbers ranging from 10 to 600 and total nanoparticles volume fraction ranging from 0.0 to 0.02 using the finite volume method. The predicted results of streamlines, isotherms, isentropic lines, average Nusselt number, average entropy generation and average Bejan number are the main focus of interest in the present paper.

Optimization of entropy generation in motion of magnetite-Fe3O4 nanoparticles due to curved stretching sheet of variable thickness

2019 ◽  
Vol 29 (9) ◽  
pp. 3347-3365
Author(s):  
Sumaira Qayyum ◽  
Tasawar Hayat ◽  
Ahmed Alsaedi
Keyword(s):  
Porous Medium ◽  
Mixed Convection ◽  
Viscous Dissipation ◽  
Entropy Generation ◽  
Variable Thickness ◽  
Stretching Sheet ◽  
Volume Fraction ◽  
Bejan Number ◽  
Content Type ◽  
Curvature Parameter

Purpose Investigation for convective flow of water-based nanofluid (composed of ferric oxide asnanoparticles) by curved stretching sheet of variable thickness is made. Bejan number andentropy generation analysis is presented in presence of viscous dissipation, mixed convectionand porous medium. Design/methodology/approach In this paper, by using NDSolve of MATHEMATICA, the nonlinear system of equations is solved. Velocity, temperature, Bejan number and entropy generation for involved dimensionless variables are discussed. Findings Increase in velocity is depicted for larger curvature parameter, and opposite trend is witnessed for higher nanoparticle volume concentration. Enhancement in temperature is seen for higher Eckert number while reverse behavior is noticed for larger curvature parameter. Entropy rate increases for variation of curvature parameter, Brinkman number and nanoparticle volume fraction. Bejan number decays for mixed convection and curvature parameters. Originality/value To the authors’ knowledge, there exists no study yet which describes flow by curved sheet of variable thickness. Such consideration with nanoparticles seems important task. Thus, the main objective here is to determine entropy generation in ferromagnetic nanofluid flow due to variable thickened curved stretching surface. Additionally, effects of Joule heating, porous medium, mixed convection and viscous dissipation are taken into account.

scholarly journals Numerical Study of Heat Transfer by Natural Convection in Concentric Hexagonal Cylinders Charged with a Nanofluid

2022 ◽  
Vol 17 ◽  
pp. 19-28
Author(s):  
Taloub Djedid ◽  
Bouras Abdelkrim ◽  
Zied Driss
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Volume Fraction ◽  
Numerical Study ◽  
Outer Cylinder ◽  
Boussinesq Approximation ◽  
Fixed Temperature ◽  
Nusselt Numbers ◽  
Volume Method ◽  
Rayleigh Numbers

In this document, a numerical study of the natural convection of steady-state laminar heat transfer in a horizontal ring between a heated hexagonal inner cylinder and a cold hexagonal outer cylinder. A Cu - water nanofluid traverses this annular space. The system of equations governing the problem was solved numerically by the fluent calculation code based on the finite volume method. Based on the Boussinesq approximation. The interior and exterior sides from the two cylinders are maintained at a fixed temperature. We investigated the impacts of various thermal Rayleigh numbers (103≤ Rat ≤2.5x105), and the volume fraction from the nanoparticles (0≤ Ø ≤0.12) on fluid flow and heat transfer performance. It is found that in high thermal Rayleigh numbers, a thin thermal boundary layer is illustrated at the flow that heavily strikes the ceiling and lower from the outer cylinder. In addition, the local and mean Nusselt number from a nanofluid are enhanced by enhancing the volume fraction of the nanoparticles.The results are shown within the figure of isocurrents, isotherms, and mean and local Nusselt numbers. Detailed results of the numerical has been compared with literature ones, and it gives a reliable agreement.

Effect of Nanofluid on Heat Transfer Enhancement for Mixed Convection Flow Over a Corrugated Surface

2020 ◽  
Vol 45 (4) ◽  
pp. 373-383
Author(s):  
Nepal Chandra Roy ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Thermal Boundary Layer ◽  
Volume Fraction ◽  
Convection Flow ◽  
Mixed Convection Flow

AbstractA mathematical model for mixed convection flow of a nanofluid along a vertical wavy surface has been studied. Numerical results reveal the effects of the volume fraction of nanoparticles, the axial distribution, the Richardson number, and the amplitude/wavelength ratio on the heat transfer of Al2O3-water nanofluid. By increasing the volume fraction of nanoparticles, the local Nusselt number and the thermal boundary layer increases significantly. In case of \mathrm{Ri}=1.0, the inclusion of 2 % and 5 % nanoparticles in the pure fluid augments the local Nusselt number, measured at the axial position 6.0, by 6.6 % and 16.3 % for a flat plate and by 5.9 % and 14.5 %, and 5.4 % and 13.3 % for the wavy surfaces with an amplitude/wavelength ratio of 0.1 and 0.2, respectively. However, when the Richardson number is increased, the local Nusselt number is found to increase but the thermal boundary layer decreases. For small values of the amplitude/wavelength ratio, the two harmonics pattern of the energy field cannot be detected by the local Nusselt number curve, however the isotherms clearly demonstrate this characteristic. The pressure leads to the first harmonic, and the buoyancy, diffusion, and inertia forces produce the second harmonic.

scholarly journals Effect of magnetic field on nanofluid free convection in Conical Partially Annular Space

2020 ◽  
Vol 330 ◽  
pp. 01005
Author(s):  
Abderrahmane AISSA ◽  
Mohamed Amine MEDEBBER ◽  
Khaled Al-Farhany ◽  
Mohammed SAHNOUN ◽  
Ali Khaleel Kareem ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Hartmann Number ◽  
Volume Fraction ◽  
Boussinesq Approximation ◽  
Simulation Software ◽  
Comsol Multiphysics ◽  
Governing Equations ◽  
Element Analysis ◽  
Vertical Side ◽  
Side Walls

Natural convection of a magneto hydrodynamic nanofluid in a porous cavity in the presence of a magnetic field is investigated. The two vertical side walls are held isothermally at temperatures Th and Tc, while the horizontal walls of the outer cone are adiabatic. The governing equations obtained with the Boussinesq approximation are solved using Comsol Multiphysics finite element analysis and simulation software. Impact of Rayleigh number (Ra), Hartmann number (Ha) and nanofluid volume fraction (ϕ) are depicted. Results indicated that temperature gradient increases considerably with enhance of Ra and ϕ but it reduces with increases of Ha.

Effects of Insulated and Isothermal Baffles on Pseudosteady-State Natural Convection Inside Spherical Containers

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Yuping Duan ◽  
S. F. Hosseinizadeh ◽  
J. M. Khodadadi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Numerical Procedure ◽  
Boussinesq Approximation ◽  
Transfer Enhancement ◽  
Nusselt Numbers ◽  
Extended Surface ◽  
Parametric Studies ◽  
Thermal Layer

The effects of insulated and isothermal thin baffles on pseudosteady-state natural convection within spherical containers were studied computationally. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables. Natural convection effect is modeled via the Boussinesq approximation. Parametric studies were performed for a Prandtl number of 0.7. For Rayleigh numbers of 104, 105, 106, and 107, baffles with three lengths positioned at five different locations were investigated (120 cases). The fluid that is heated adjacent to the sphere rises replacing the colder fluid, which sinks downward through the stratified stable thermal layer. For high Ra number cases, the hot fluid at the bottom of the sphere is also observed to rise along the symmetry axis and encounter the sinking colder fluid, thus causing oscillations in the temperature and flow fields. Due to flow obstruction (blockage or confinement) effect of baffles and also because of the extra heating afforded by the isothermal baffle, multi-cell recirculating vortices are observed. This additional heat is directly linked to creation of another recirculating vortex next to the baffle. In effect, hot fluid is directed into the center of the sphere disrupting thermal stratified layers. For the majority of the baffles investigated, the Nusselt numbers were generally lower than the reference cases with no baffle. The extent of heat transfer modification depends on Ra, length, and location of the extended surface. With an insulated baffle, the lowest amount of absorbed heat corresponds to a baffle positioned horizontally. Placing a baffle near the top of the sphere for high Ra number cases can lead to heat transfer enhancement that is linked to disturbance of the thermal boundary layer. With isothermal baffles, heat transfer enhancement is achieved for a baffle placed near the bottom of the sphere due to interaction of the counterclockwise rotating vortex and the stratified layer. For some high Ra cases, strong fluctuations of the flow and thermal fields indicating departure from the pseudosteady-state were observed.

Mixed convection flow of an electrically conducting fluid in a vertical channel with boundary conditions of the third kind

2014 ◽  
Vol 92 (11) ◽  
pp. 1387-1396 ◽  
Author(s):  
J.C. Umavathi ◽  
A.J. Chamkha
Keyword(s):  
Mixed Convection ◽  
Average Velocity ◽  
Vertical Channel ◽  
Perturbation Parameter ◽  
Conducting Fluid ◽  
Integration Scheme ◽  
Electrically Conducting ◽  
Nusselt Numbers ◽  
Electrically Conducting Fluid ◽  
External Fluid

In this study, the effects of viscous and Ohmic dissipation in steady, laminar, mixed, convection heat transfer for an electrically conducting fluid flowing through a vertical channel is investigated in both aiding and opposing buoyancy situations. The plates exchange heat with an external fluid. Both conditions of equal and different reference temperatures of the external fluid are considered. First, the simpler cases of either negligible Brinkman number or negligible Grashof number are addressed with the help of analytical solutions. The combined effects of buoyancy forces and viscous dissipation are analyzed using a perturbation series method valid for small values of the perturbation parameter. To relax the conditions on the perturbation parameter, the governing equations are also evaluated numerically by a shooting technique that uses the classical explicit Runge–Kutta method of four slopes as an integration scheme and the Newton–Raphson method as a correction scheme. In the examined cases of velocity and temperature fields, the Nusselt numbers at both the walls and the average velocity are explored. It is found that the velocity profiles for an open circuit (E > 0 or E < 0) lie in between the short circuit (E = 0). The graphical results illustrating the effects of various parameters on the flow as well as the average velocity and Nusselt numbers are presented for open and short circuits. In the absence of electric field load parameter and Hartmann number, the results agree with Zanchini (Int. J. Heat Mass Transfer, 41, 3949 (1998)). Further, the analytical and numerical solutions agree very well for small values of the perturbation parameter.

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