Showing papers on "Combined forced and natural convection published in 2019"
TL;DR: In this article, the authors examined the effects of Al2O3/water hybrid nanofluid on the mixed convection inside a square cavity caused by a hot oscillating cylinder and found that the motion of the cylinder toward the top and bottom walls increases the average Nusselt number when the Rayleigh number is low.
Abstract: The aim of this paper is to examine the effects of Cu–Al2O3/water hybrid nanofluid and Al2O3/water nanofluid on the mixed convection inside a square cavity caused by a hot oscillating cylinder. The governing equations are first transformed into dimensionless form and then discretized over a non-uniform unstructured moving grid with triangular elements. The effects of several parameters, such as the nanoparticle volume fraction, the Rayleigh number, the amplitude of the oscillation, and the period of the oscillation of the cylinder are investigated numerically. The results indicate that the motion of the oscillating cylinder toward the top and bottom walls increases the average Nusselt number when the Rayleigh number is low. Furthermore, the presence of Al2O3 and Cu–Al2O3 nanoparticles leads to an increase in the values of the average Nusselt number Nuavg for cases of low values of the Rayleigh number. It is found that the natural convection heat transfer rate of a simple Al2O3/water nanofluid is better than that of Cu–Al2O3/water hybrid nanofluid.
170 citations
TL;DR: In this article, a two-phase model was used to simulate Newtonian fluid flow and heat transfer in a cavity with rotating cylinders and the effect of the presence of the cylinder on the cavity in stationary and rotating states on the flow field and the increase of the heat transfer rate was studied.
127 citations
TL;DR: In this article, a two-phase mixed convection of a non-Newtonian nanofluid in a porous H-shaped cavity was studied, where different aspect ratios were used in order to achieve the best heat transfer rate.
122 citations
TL;DR: In this paper, the effect of angular velocity on heat transfer of non-Newtonian power-law nanofluid including CuO nanoparticles inside a partially porous square enclosure with a concentric rotating cylinder and a hot side wall is numerically investigated.
Abstract: In this study, mixed convection heat transfer of the non-Newtonian power-law nanofluid including CuO nanoparticles, inside a partially porous square enclosure with a concentric rotating cylinder and a hot side wall is numerically investigated. Two-phase mixture model is utilized for nanofluid flow simulation and the mixture viscosity and thermal conductivity are computed by Corcione’s correlation. The effect of different angular velocity (− 4000 ≤ Ω ≤ 4000) for various Rayleigh (104 ≤ Ra ≤ 106), Darcy (10−4 ≤ Da ≤ 10−1), power-law index (0.8 ≤ n ≥ 1.2) and effective to base fluid thermal conductivity ratio (keff/kf= 16, 4) are studied on heat transfer. Results are presented and compared in terms of the average Nusselt number, and streamline and isotherm contours. Outcomes show that for different kinds of fluid, depending on the value of Ra, Da, keff/kf and the amount and direction of angular velocity, heat transfer can be improved by augmenting heat convection and also can be deteriorated by increasing viscosity. Consequently, optimal values of Ra, Da, keff/kf and Ω exist in order to maximize the average Nu number.
120 citations
TL;DR: In this paper, the authors investigated the thermal behavior of nano-encapsulated phase change materials (NEPCMs) dispersed in a liquid over a vertical flat plate and found that the presence of NEPCM particles enhances the heat transfer over the plate.
113 citations
TL;DR: In this paper, the authors reviewed all the published studies about mixed convection of nanofluids in enclosures and categorized them into four main classes, namely square (and rectangular), triangular, trapezoidal, and unconventional shapes.
110 citations
TL;DR: In this article, the authors scrutinize the up-to-date advances in nanofluids by utilizing the properties of nonlinear mixed convection and binary chemical reaction with Arrhenius activation energy in time-dependent Carreau flow.
102 citations
Book•
10 Jul 2019
TL;DR: In this paper, the authors describe a thermal convection with LTNE and LTNE with double diffusive convection in a Porous Layer with Solid Partitions. But they do not discuss the effect of LTNE on the dynamics of the Porous Media.
Abstract: Introduction.- Thermal Convection with LTNE.- Rotating Convection with LTNE.- Double Diffusive Convection with LTNE.- Vertical Porous Convection with LTNE.- Penetrative Convection.- LTNE and Multi-layers.- Other Convection/Microfluidic Scenarios.- Convection with Slip Boundary Conditions.- Convection in a Porous Layer with Solid Partitions.- Convection with Produting Baffles.- Anisotropic Inertia Effect.- Bidispersive Porous Media.- Resonance in Thermal Convection.- Thermal Convection in Nanofluids.- References.
100 citations
TL;DR: In this article, a mixed convection micropolar fluid flow in porous medium with uniform magnetic field towards nonlinear stretched surface was analyzed in the presence of viscous dissipation, Joule heating and convective boundary condition.
85 citations
TL;DR: In this article, the authors examined the entropy generation effectiveness in hydromagnetic flow of viscous fluid by permeable rotating disk and proposed a new chemically reacted species model featuring activation energy is taken into account.
84 citations
TL;DR: In this paper, the steady flow of incompressible, viscous, conducting and optically thin fluid over a vertical plate with magnetohydrodynamic mixed convection, thermal radiation and viscous dissipation was investigated.
TL;DR: In this paper, the effect of the presence of a magnetic field on the rate of convective heat transfer and entropy generation of a hybrid nanofluid (water/Al2O3-CuO (50/50)) in a square diagonal cavity was examined.
Abstract: In this paper, a numerical study has been examined on the effect of the presence of a magnetic field on the rate of convective heat transfer and entropy generation of a hybrid nanofluid (water/Al2O3-CuO (50/50)) in a square diagonal cavity. The horizontal walls of the insulating cavity and fixed temperature source are set on the left and right vertical wall with cold temperature. The governing equations are solved by finite volume method using the SIMPLE algorithm. In this paper, the effect of the Richardson number, Hartman number, thermal source length on hybrid entropy generation and convective heat transfer rate has been examined. Using the Response Surface Methodology (RSM) method, a polynomial equation is obtained between the three parameters given for the Nusselt number, total entropy generation and Bejan number. Then the sensitivity of responses to factors is checked. Finally, depending on the importance of each of the responses, we use the optimal points where simultaneously the highest Nu number, the lowest entropy generation, and Bejan number occur. The results show that with increasing Richardson number, heat transfer rate is reduced, and this reduction is more pronounced in smaller Hartmann number. Also, total entropy generation increased with increasing Richardson number, but Bejan number reduced. With increasing the intensity of the magnetic field and reducing the length of the thermal source, the heat transfer rate also reduces. However, with increasing the intensity of the magnetic field, the total entropy generation and Bejan number increase. Also, with increasing the length of the thermal source, the total entropy generation and Bejan number increase.
TL;DR: In this paper, the transient entropy generation and mixed convection due to a rotating hot inner cylinder within a square cavity having a flexible side wall by using the finite element method and arbitrary Lagrangian-Eulerian formulation was investigated.
TL;DR: In this paper, numerical analysis of mixed convection of CuO-water nanofluid in a cavity with inlet and outlet ports is performed under the effects of inclined magnetic field and step like corrugated elastic walls.
TL;DR: In this article, the authors studied the problem of time-dependent heat transfer of alumina-water nanoliquid within a differentially heated chamber with isothermal moving vertical walls and adiabatic horizontal ones under the impact of an inner solid cylinder.
TL;DR: In this article, the effects of changes in the value of imposed angular velocity (in terms of Richardson number), non-Newtonian power-law index, Rayleigh number and nanofluid volume fraction on both the heat transfer and entropy generation are discussed.
TL;DR: The main purpose of this study is to investigate the multislip effects on the magneto-hydrodynamic mixed convection unsteady flow of micropolar nano-fluids over a stretching/shrinking sheet along with radiation in the presence of a heat source.
Abstract: The main purpose of this study is to investigate the multislip effects on the magneto-hydrodynamic (MHD) mixed convection unsteady flow of micropolar nano-fluids over a stretching/shrinking sheet along with radiation in the presence of a heat source. The consequences of multislip and buoyancy conditions have been integrated. By using the suitable similarity variables are used to solve the governing non-linear partial differential equations into a system of coupled non-linear ordinary differential equations. The transformed equations are solved numerically by using Runge–Kutta fourth-order method with shooting technique. The impacts of the several parameters on the velocity, temperature, micro-rotation, and concentration profiles as well as on the skin friction coefficient, Sherwood number, and Nusselt number are discussed with the help of graphs and tables.
TL;DR: In this article, a two-sided lid-driven cavity filled with heterogeneous porous media is optimized to maximize Nuavg of the flow for various Rayleigh (Ra) and Richardson (Ri) numbers.
Abstract: Mixed convection of Cu–water nanofluid inside a two-sided lid-driven cavity filled with heterogeneous porous media is optimized. The horizontal walls are adiabatic and movable, and the vertical walls are exposed to constant hot and cold temperatures. Two-phase mixture model and Darcy–Brinkman–Forchheimer relation are implemented, respectively, for simulation of nanofluid and fluid flow through porous media. Pores size diameters of the porous medium in different regions are considered as decision variables for optimization process. In this regard, the cavity is divided into 25 parts, and the pore size of each part is found through the pattern search optimization algorithm. The optimization is performed in order to maximize Nuavg of the flow for various Rayleigh (Ra = 103–106) and Richardson (Ri = 0.01, 0.1, 1, 10 and 100) numbers. Gaining the optimized heterogeneous structure of the porous medium in which Nuavg is greater than that of the homogeneous medium with the highest Nusselt (
$${\text{Nu}}_{{{\text{dp}}_{ \hbox{max} } }}$$
) is the main goal of optimization. Results indicate that for more convection dominated flows (lower Ri and higher Ra numbers), the optimized heterogeneous porous medium could enhance heat transfer up to 8.3%. But the optimal porous medium for natural convection dominated flows (high Ri and low Ra values) is the homogeneous porous case with maximum pore size diameter. Furthermore, drag force on the driven lid increased up to 0.34% for the optimal cases which is very low and can be disregarded.
TL;DR: In this article, the authors studied the steady mixed convection hybrid nanofluid flow and heat transfer past a vertical thin needle with prescribed surface heat flux, where the governing partial differential equations are transformed into a set of ordinary differential equations by using a similarity transformation.
Abstract: The purpose of this paper is to study the steady mixed convection hybrid nanofluid flow and heat transfer past a vertical thin needle with prescribed surface heat flux.,The governing partial differential equations are transformed into a set of ordinary differential equations by using a similarity transformation. The transformed equations are then solved numerically using the boundary value problem solver (bvp4c) in Matlab software. The features of the skin friction coefficient and the local Nusselt number as well as the velocity and temperature profiles for different values of the governing parameters are analyzed and discussed.,It is found that dual solutions exist for a certain range of the mixed convection parameter where its critical values decrease with the increasing of the copper (Cu) nanoparticle volume fractions and for the smaller needle size. It is also observed that the increasing of the copper (Cu) nanoparticle volume fractions and the decreasing of the needle size tend to enhance the skin friction coefficient and the local Nusselt number on the needle surface. A temporal stability analysis is performed to determine the stability of the dual solutions in the long run, and it is revealed that only one of them is stable, while the other is unstable.,The problem of hybrid nanofluid flow and heat transfer past a vertical thin needle with prescribed surface heat flux is the important originality of the present study where the dual solutions for the opposing flow are obtained.
TL;DR: In this paper, the authors used the Lagrangian-Eulerian method to describe the fluid motion within the cavity for the flexible fin attached to its upper wall under the influence of an inclined magnetic field.
Abstract: In this study, fluid flow and heat transfer in a vertical lid-driven CuO–water nanofluid filled square cavity with a flexible fin attached to its upper wall under the influence of an inclined magnetic field are numerically investigated. The left vertical wall of the cavity is colder than right vertical wall, and it moves in + y direction with constant speed. Horizontal walls of the cavity are insulated. The governing equations are solved with finite element method. The arbitrary Lagrangian–Eulerian method is used to describe the fluid motion within the cavity for the flexible fin in the fluid-structure interaction model. The influence of Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of the magnetic field (between 0 and 90%), nanoparticle volume fraction (between 0 and 0.05) and Young’s modulus of flexible fin (between 250 and 5000) on the flow and heat transfer were numerically studied. It is observed that the presence of the elastic fin affects the flow field and thermal characteristics of the cavity. The local and average heat transfer enhance as the Richardson number, solid volume fraction of the nanoparticle increase whereas deteriorate as the value of the Hartmann number and inclination angle of the magnetic field increases due to the dampening of the fluid motion with Lorentz forces. The addition of the nanoparticles is more effective along the lower part of the right vertical wall where the heat transfer process is effective. The average heat transfer increases by 28.96% for solid volume fraction of 0.05% compared to base fluid when the flexible fin is attached to the upper wall. The average heat transfer deteriorates by 10.10% for cavity with and without fin at Hartmann number of 50 compared to the case without magnetic field. The average heat transfer enhances as the Young’s modulus of the flexible fin decreases and the average Nusselt number increases by 13.24% for Young’s modulus of 250 compared to configuration for the cavity having the Young’s modulus of 5000.
TL;DR: In this paper, a framework is established to deal the characteristics of axisymmetric mixed convection flow with heat transfer of water based copper (Cu-water) nanofluid along a porous shrinking cylinder with slip effects.
TL;DR: In this article, a new local heat transfer correlation accounting for the thermophysical property variations and the buoyancy effects has been developed based on analysis of thermophysical properties and the effect of buoyancy on the heat transfer performance of the printed circuit heat exchanger (PCHE) geometries during cooling under forced and mixed convection conditions.
TL;DR: In this paper, the influence of partial slip on entropy generation in a U-shaped cavity with discrete heating was simulated and the results showed that the average Nusselt number increases with the increase in the volume fraction of nanoparticles at AR = 0.1.
Abstract: This contribution simulates the impact of partial slip on entropy generation due to magnetohydrodynamic, mixed convection of nanofluids in a lid-driven U-shaped cavity with discrete heating. The influence of the partial slip effect is proposed along the lid-driven vertical walls. A uniform heat flux source on the bottom wall is proposed; meanwhile, the two portions of the outer-upper horizontal walls are cooled isothermally. The remainder cavity walls are taken adiabatic. The governing equations are solved using the finite volume approach, and the outcomes are successfully validated against previous studies. Simulation results are presented and discussed for several cases with the impacts of the governing parameters on the heat transfer rate. Inspection of the results in mixed convective and entropy generation environments demonstrate that the average Nusselt number increases with the increase in the volume fraction of nanoparticles at AR = 0.1. For all values of D (heat source location), the Nusselt number increases by crossing the heat source and reaches its maximum value at the end of the source. Also, for all values of the aspect ratio, addition of nanoparticles into the base fluid leads to a loss in the thermal performance. Moreover, for all states of movement, addition of nanoparticles into the base fluid leads to an increase in the entropy.
TL;DR: In this article, the authors numerically examined mixed convection of CuO-water nanofluid in a 3D vented cavity with inlet and outlet ports under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects.
Abstract: This study aims to numerically examine mixed convection of CuO-water nanofluid in a three-dimensional (3D) vented cavity with inlet and outlet ports under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.,The bottom surface is corrugated with a rectangular wave shape, and the rotating cylinder surface and cavity bottom surface were kept at constant hot temperatures while the cold fluid enters the inlet port with uniform velocity. The complicated interaction between the forced convection and buoyancy-driven convection coupled with corrugated and rotating surfaces in 3D configuration with magnetic field, which covers a wide range of thermal engineering applications, are numerically simulated with finite element method. Effects of various pertinent parameters such as Richardson number (between 0.01 and 100), Hartmann number (between 0 and 1,000), angular rotational speed of the cylinder (between −30 and 30), solid nanoparticle volume fraction (between 0 and 0.04), corrugation height (between 0 and 0.18H) and number (between 1 and 20) on the convective heat transfer performance are numerically analyzed.,It was observed that the magnetic field suppresses the recirculation zone obtained in the lower part of the inlet port and enhances the average heat transfer rate, which is 10.77 per cent for water and 6.86 per cent for nanofluid at the highest strength. Due to the thermal and electrical conductivity enhancement of nanofluid, there is 5 per cent discrepancy in the Nusselt number augmentation with the nanoadditive inclusion in the absence and presence of magnetic field. The average heat transfer rate of the corrugated surface enhances by about 9.5 per cent for counter-clockwise rotation at angular rotational speed of 30 rad/s as compared to motionless cylinder case. Convective heat transfer characteristics are influenced by introducing the corrugation waves. As compared to number of waves, the height of the corrugation has a slight effect on the heat transfer variation. When the number of rectangular waves increases from N = 1 to N = 20, approximately 59 per cent of the average heat transfer reduction is achieved.,In this study, mixed convection of CuO-water nanofluid in a 3D vented cavity with inlet and outlet ports is numerically examined under the influence of an inner rotating circular cylinder, homogeneous magnetic field and surface corrugation effects. To the best of authors knowledge such a study has never been performed. In practical applications, it is possible to encounter some of the considered configurations in a vented cavity such as magnetic field, rotating cylinder and it is also possible to specially add some of the active and passive control means to control the convection inside the cavity such as adding nanoparticles, corrugating the surfaces. The complicated physics with nanofluid under the effects of magnetic field and inclusion of complex 3D geometry make it possible to use the results of this numerical investigation for the design, control and optimization of many thermal engineering systems as mentioned above.
TL;DR: In this paper, a tangent hyperbolic viscoelastic fluid model has been used in presence of nanoparticles which may extremely useful to enhance the transportation phenomenon and second order slip effects (Wu's slip) are also entertained in the boundary conditions.
Abstract: Current study deals with the rheology of non-Newtonian material over moving surface by utilizing the electrical, megnetohydrodynaimcs and activation energy effects. A famous tangent hyperbolic viscoelastic fluid model has been used in presence of nanoparticles which may extremely useful to enhance the transportation phenomenon. The second order slip effects (Wu's slip) are also entertained in the boundary conditions. Further, the energy equation occupied the nonlinear thermal radiation while the activation energy expression is carried out in the concentration equation. The highly non-linear boundary value problem is metamorphosed into ordinary differential equations by means of the suitable variables. These transmuted equations results the self-similar solution which is computed numerically by shooting technique. First, the reported solution is justified after comparing with available resources and detail graphical analysis have been executed for parameters like Weissenberg number (We) mixed convection buoyancy parameters (Gr,Gc), the power law index (n), thermophoresis (Nt), Brownian constraint (Nb) and slip parameters (?,?). Further, the impact of suggested parameters on local Nusselt number and Sherwood number is determined in tabular form. It is found that the slip parameters resulted the weaker momentum boundary layer. The nanoparticles temperature is enhanced by the increasing values of thermophoresis and Brownian motion parameters, Weissenberg and thermal Biot numbers. Further, the convection parameters decrease the nanoparticles concentration while presence of activation energy slightly boosts up the nanoparticles concentration.
TL;DR: In this article, a generialzied homogenous flow model that describes hybrid nanofluids containing multiple kinds of nanoparticles is developed for modeling the problem and its simplified form is proposed based on linear assumptions and verified by existing model.
TL;DR: In this article, a steady laminar two-dimensional magneto-hydrodynamics mixed convection flow in a square inclined cavity filled with Cu-water nanofluid is investigated numerically by using the finite difference method.
Abstract: A steady laminar two-dimensional magneto-hydrodynamics mixed convection flow in a square inclined cavity filled with Cu–water nanofluid is investigated numerically by using the finite difference method. The left and right vertical sidewalls of the cavity are considered adiabatic and move upward, while a partial slip flow condition is imposed on these walls. The horizontal top wall is considered cold and stationary, while a part of the stationary bottom wall is subjected to a uniform heat source and the remaining parts of it are considered adiabatic. An adiabatic obstacle is located in the center of the cavity and an external magnetic field is applied parallel to the horizontal x-axis. Parametric studies of the influence of various parameters such as Hartmann number, inclination angle of the cavity, dimensionless heat generation/absorption coefficient, obstacle aspect ratio, dimensionless length and location of the heat source, and solid volume fraction on the fluid flow and heat transfer have been performed. Comparisons with previously published numerical work are performed, and good agreements between the results are observed. It is found that the nanofluid was better than water to enhance the heat transfer when the effect of the magnetic field is weak, while the water is better than the nanofluid when its effect is strong. Moreover, the results indicated that the partial slip has a significant effect on the above-mentioned parameters.
TL;DR: In this paper, the impingement of CuO-water nanofluid flows upon a cylinder subject to a uniform magnetic field with constant surface temperature and embedded in porous media is investigated for the first time in literature.
Abstract: The impingement of CuO-water nanofluid flows upon a cylinder subject to a uniform magnetic field with constant surface temperature and embedded in porous media is investigated for the first time in literature. The surface of the cylinder can feature uniform or non-uniform mass transpiration and is hotter than the incoming nanofluid flow. The gravitational effects are taken into account and the three-dimensional governing equations of mixed convection in curved porous media, under magnetohydrodynamic effects, are reduced to those solvable by a finite difference scheme. Through varying a mixed convection parameter, the situations dominated by forced, mixed and free convection are examined systematically. The numerical solutions of these equations reveal the flow velocity and temperature fields as well as the Nusselt number and induced shear stress. These are then used to calculate the rate of entropy generation within the system by viscous and heat transfer irreversibilities. The results show that Nusselt number increases with increasing the concentration of nanoparticles, while it slightly deceases through intensifying the magnetic parameter. Non-uniform transpiration is shown to strongly affect the average rate of heat transfer. Importantly, it is demonstrated that the specific mode of heat convection can majorly influence the intensity of entropy generation and that the irreversibilities are much larger under natural convection compared to those in mixed and forced convection. Calculation of Bejan number shows that this is due to more pronounced relative contribution of viscous irreversibilities when free convection effects dominate the mixed convection process.
TL;DR: In this paper, the authors performed numerical simulation of mixed convection heat transfer in a lid-driven triangular cavity filled with power law nanofluid and with an opening under the effect of an inclined magnetic field.
Abstract: Numerical simulation of mixed convection heat transfer in a lid-driven triangular cavity filled with power law nanofluid and with an opening was performed under the effect of an inclined magnetic field. The left vertical wall of the cavity moves in + y-direction, and the bottom wall of the cavity is partially heated. Galerkin weighted residual finite element method was used to solve the governing equations. Influence of Richardson number, Hartmann number, inclination angle, opening ratio and nanoparticle volume fraction on the fluid flow and heat transfer is examined for various power law indices. It was observed that average heat transfer deteriorates as the value of Richardson number and Hartmann number enhances. At the lowest value of Richardson number, the discrepancy between the average heat transfer corresponding to different power law indices is higher. The inclination angle of the magnetic field where the minimum of the average Nusselt number is seen depends on the fluid type. Average heat transfer number is the highest for the highest value of the opening ratio. The average Nusselt number enhances with solid particle volume fraction, and there are slight variations in the reduction in the average Nusselt number when base fluid and nanofluid are considered for various power law indices.