Etude numérique de la convection mixte lors de l'écoulement d'un nanofluide hybride (Ag-MgO/Eau) dans une cavité trapézoïdale ventilée soumise à l'action d'un champ magnétique

The goal of this numerical study, is to investigate the hydromagnetic mixed convection heat transfer flow inside a ventilated cavity, crossed by hybrid nanofluid. This latter is made of Ag and MgO nanoparticles (50:50 vol %) dispersed in water as base fluid. The enclosure is under the influence of a uniform and constant magnetic field, applied in a horizontal direction. In this work, the cavity is of right angled trapezoid shape, and is assumed to be of infinite length in the third direction imparting a two-dimensional character to the flow. The cavity is subjected to a laminar and steady jet of fresh hybrid nanofluid entering the enclosure through an opening placed on the lower corner of the bottom wall which is adiabatic, just like the vertical right wall. The fluid is evacuated through an opening representing the upper base of the cavity. The left wall is inclined, and is maintained at a constant and uniform hot temperature. It is assumed that the nanofluid is Newtonian, incompressible and substantially behaves as a single phase fluid. Moreover, the Boussinesq approximation is valid for buoyancy force. New correlations to predict the viscosity and thermal conductivity of Ag-MgO / water hybrid nanofluid are employed in the study. The dimensionless governing equations with the appropriate boundary conditions, are discretized by the finite volume method and solved numerically via the SIMPLER algorithm. All the simulations were performed for the case of pure mixed convection (Ri = 1), and are presented on the one hand, through hydrodynamic and thermal fields in the cavity as well as the velocity profiles. On the other hand, a special focus is granted to the heat transfer rate, through the evaluation of the average Nusselt number at the hot inclined wall. The study focuses on the determination of the conditions that provide the best thermal performance of the cavity. We investigate the effect of some parameters including the influence of the hybrid nanofluid jet intensity (Reynolds number), the magnetic field strength (Hartmann number) and nanoparticles volume fraction. The results indicate that the hybrid nanofluid flow is strongly affected by the increase in the intensity of the magnetic field. Globally, the augmentation of Reynolds and Hartmann numbers enhance the heat transfer rate. We also note that, the increase in nanoparticles concentrations promotes the heat transfer. However, the contribution of nanoparticles on the improvement of heat transfer has a significant impact at low values of the Reynolds number

Simulation of Natural Convection in a horizontal channel with heat sources mounted with porous blocks by the lattice Boltzmann method (MRT-LBM)

In this paper, laminar natural convection in a horizontal channel provided with porous blocks periodically distributed on its lower adiabatic surface has been analyzed. This numerical study is based on the multiple-relaxation-time (MRT) Lattice Boltzmann method (LBM). The two-dimensional model D2Q9 is adopted to solve the flow field, while the D2Q5 model is applied to solve the temperature field. The objective of the study is to analyze the effect of the Darcy number (10-1 ≤ Da ≤ 10-6), Rayleigh number (103 ≤ Ra ≤ 107) and the relative porous blocks height (1/8 ≤ D ≤ 1/2). The obtained results show the important effect of these parameters, which cannot be neglected, on both flow and the heat transfer structure, within this kind of channels

Simulation of Natural Convection in a horizontal channel with heat sources mounted with porous blocks by the lattice Boltzmann method (MRT-LBM)

In this paper, laminar natural convection in a horizontal channel provided with porous blocks periodically distributed on its lower adiabatic surface has been analyzed. This numerical study is based on the multiple-relaxation-time (MRT) Lattice Boltzmann method (LBM). The two-dimensional model D2Q9 is adopted to solve the flow field, while the D2Q5 model is applied to solve the temperature field. The objective of the study is to analyze the effect of the Darcy number (10-1 ≤ Da ≤ 10-6), Rayleigh number (103 ≤ Ra ≤ 107) and the relative porous blocks height (1/8 ≤ D ≤ 1/2). The obtained results show the important effect of these parameters, which cannot be neglected, on both flow and the heat transfer structure, within this kind of channels

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

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

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

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

Magnetic field impact on nanofluid convective flow in a vented trapezoidal cavity using Buongiorno's mathematical model

Numerical study for the effect of an external magnetic field on the mixed convection of Al2O3–water Newtonian nanofluid in a right-angle vented trapezoidal cavity was performed using the finite volume method. The non-homogeneous Buongiorno model is applied for numerical description of the dynamic phenomena inside the cavity. The nanofluid, with low temperature and high concentration, enters the cavity through the upper open border, and is evacuated through opening placed at the right end of the bottom wall. The cavity is heated from the inclined wall, while the remainder walls are adiabatic and impermeable to both the base fluid and nanoparticles. After validation of the model, the analysis was carried out for a wide range of Hartmann number (0 ≼ Ha ≼ 100) and nanoparticles volume fraction (0 ≼ ϕ0 ≼ 0.06). The flow behavior as well as the temperature and nanoparticles distribution shows a particular sensitivity to the variations of both the Hartmann number and the nanofluid concentration. The domination of conduction mechanism at high Hartmann numbers reflects the significant effect of Brownian diffusion which tends to uniform the distribution of nanoparticles in the domain. The average Nusselt number which increases with the nanoparticles addition, depends strongly on the Hartmann number. Finally, a correlation predicting the average Nusselt number within such geometry as a function of the considered parameters is proposed

Double-diffusive mixed convection of pseudoplastic fluids in an inclined square cavity partially heated

Mixed convection heat and mass transfer in an inclined square cavity partially heated is numerically studied in the present paper. The cavity is filled with a non-Newtonian pseudoplastic fluid. The governing equations are solved numerically using the finite volume method. The velocitypressure coupling is achieved using the SIMPLER algorithm. This study focuses on the effect of some parameters, namely, the Richardson number and the power law index, on the flow pattern as well as on heat and mass transfer rates. The results indicate that the increase of the Richardson number decreases both heat and mass transfer rates. However, the latter are improved with the increase of the power law index whatever the value of the Richardson number

Heat transfer analysis of nanofluid flow through backward facing step

This paper presents the numerical predictions of hydrodynamic and thermal characteristics of nanofluid flow through backward facing step. The governing equations are solved through the finite volume method, as described by Patankar, by taking into account the associated boundary conditions. Empirical relations were used to give the effective dynamic viscosity and the thermal conductivity of the nanofluid. Effects of different key parameters such as Reynolds number, nanoparticle solid volume fraction and nanoparticle solid diameter on the heat transfer and fluid flow are investigated. The results are discussed in terms of the average Nusselt number and streamlines

Heat transfer analysis of nanofluid flow through backward facing step

This paper presents the numerical predictions of hydrodynamic and thermal characteristics of nanofluid flow through backward facing step. The governing equations are solved through the finite volume method, as described by Patankar, by taking into account the associated boundary conditions. Empirical relations were used to give the effective dynamic viscosity and the thermal conductivity of the nanofluid. Effects of different key parameters such as Reynolds number, nanoparticle solid volume fraction and nanoparticle solid diameter on the heat transfer and fluid flow are investigated. The results are discussed in terms of the average Nusselt number and streamlines

MRT-LBM simulation of natural convection in square annulus with a porous coating: route to chaos

In this work, multiple-relaxation-time lattice Boltzmann method is applied for examining transient natural convection in a square annulus of circular interior cylinder. This duct is covered by a porous deposit on all interior walls. The Darcy-Brinkman-Forchheimer equation is implemented to model the momentum equations in the porous matrix and the Boussinesq approximation is assumed for buoyancy term. The impact of Darcy number (10−6 ≤ Da ≤ 10−2), Rayleigh number (Ra ≥ 101), radius ratio of the circular cylinder (0.05 ≤ R ≤ 0.40) and the thickness of the porous layer (0.05 ≤ δ ≤ 0.15) on natural convection are analysed. The outcomes are represented under the form of stream functions, isotherms and mean Nusselt number. In addition, temporal evolution and phase portrait are plotted to examine the unsteady flow at elevated Rayleigh numbers. The results are coherent and show that natural convection develops from stable state to chaotic flow via periodic and quasi-periodic oscillatory regimes as the Rayleigh number increases