Search

The present study explores nanofluid magnetohydrodynamics (MHD) natural convection in an incinerator shaped enclosure including a rectangular hot block situated on the bottom wall. A parametric investigation is conducted to explore the effect of different parameters such as nanoparticles volume fraction ( ϕ  = 0–4%), Rayleigh number (Ra = 10 3 –10 5 ), external magnetic field intensity (Ha = 0–100), incinerator tilting angle ( γ  = 0–360°) and hot block's height (0.1–0.5), width (0.1–0.8) and position on heat transfer, nanofluid flow, and entropy generation inside the incinerator. The top and bottom horizontal walls of enclosure are adiabatic; the right, left vertical and inclined walls are supposed to have cold temperature whereas the hot block is maintained at a hot temperature. The Brownian motion was also considered in calculating the effective nanofluid thermal conductivity and viscosity using Koo–Kleinstreuer–Li (KKL) correlation. The lattice-Boltzmann method is used with a D2Q9-D2Q9 double population's model as utilized CFD approach. The mesh independency study and the validation of proposed model are accomplished in several cases and very good agreement is found between present results and former experimental and numerical findings. The results showed that entropy generation is augmented by increasing height and width of heater, nanoparticles volume fraction and Rayleigh number but it is reduced by enhacing Hartmann number. However, increasing the magnetic field does not have notable influence on heat transfer, compared to other parameters. The optimum incinerator inclination angles to maximize heat transfer and minimize entropy generation are 90° and 270°. [ABSTRACT FROM AUTHOR]

The present work reports a numerical study of natural convection in an incinerator shaped enclosure with a localized heated source situated at the bottom. Lattice Boltzmann Method (LBM) is used to simulate nanofluid (water-Al2O3) flow and heat transfer. Simulations have been carried out for the pertinent parameters: Rayleigh number (Ra=103-106), solid volume fraction 0≤ϕ≤ 6% relative heat source high (0≤δ≤0.5), relative heat source width (0.02≤ε≤0.8), and inclination angle of the incinerator (0≤γ≤360°). The comparison of the obtained results is in excellent agreement with results from literature. It may be noted that the Rayleigh number, the solid volume fraction, the heat source tallness enhances the heat transfer and influences the flow pattern and the thermal structures. However for the relative heat source width plays opposite role for values superior to 0.4. [ABSTRACT FROM AUTHOR]

In this study, Magneto-Hydro-Dynamic (MHD) natural convection heat transfer has been analyzed for an inclined C-shaped cavity filled with nanofluid. The Lattice Boltzmann Method (LBM) is used to solve the governing equations. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo-Kleinstreuer-Li) correlation. The influence of pertinent parameters such as Rayleigh number, Hartmann number, the cavity inclination angle, nanoparticle volume concentration and the cavity aspect ratio on the flow and heat transfer characteristics have been examined. From this work, it is found that the heat transfer enhances when considering the Brownian motion effect of nanoparticles, whereas presence of magnetic field tries to retard convection. Moreover, the numerical results demonstrate that the average Nusselt is increased when increasing cavity aspect ratio, cavity angle and volume fraction of nanofluid. Also, the results demonstrate that the enclosure with an inclination angle of γ = π/2, has the maximum heat transfer coefficient. [ABSTRACT FROM AUTHOR]

This paper presents the results of a numerical study on the natural convection of AI2O3-H2O nanofluid in an L-shaped cavity in the presence of a uniform magnetic field. The Lattice Boltzmann Method (LBM) is used to solve the governing equations. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo-Kleinstreuer-Li) correlation. The influence of pertinent parameters such as Rayleigh number (104≥Ra≥106), Hartmann number (0≥Ha≥60), nanoparticle volume concentration (0≥ø≥0.04) and the cavity aspect ratio (0.2≥AR ≥0.5) on the flow and heat transfer characteristics have been examined. The heat transfer increases first, then considering the role of Brownian motion of nanoparticles and increases with increasing of volume fraction of nanoparticles. But, on the contrary, Hartmann number and aspect ratio of the cavity have others important improvement factor for decreasing free convection in the enclosures. [ABSTRACT FROM AUTHOR]

In this numerical work, natural convection of CuO–water nanofluid and pure water in a cavity submitted to different heating modes on its vertical walls, is analyzed using the Lattice Boltzmann Method (LBM). The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. The influence of pertinent parameters such as Rayleigh number ( Ra = 10 3 –10 6 ), Hartmann number ( Ha = 0–80), heat generation or absorption coefficient ( q = − 10, − 5, 0, 5, 10) and nanoparticle volume concentration ( ϕ = 0–0.04) on the flow and heat transfer characteristics has been examined. In general, by considering the role of Brownian motion, the enhancement in heat transfer is observed at any Hartman and Rayleigh numbers. In addition, the heat generation or absorption influences the heat transfer in the cavity at Ra = 10 3 more than other Rayleigh numbers as the least effect is observed at Ra = 10 6 . [ABSTRACT FROM AUTHOR]

In this numerical work, MHD natural convection of Cu–water nanofluid and pure water in a cavity with the left wall being linearly heated is analyzed using the Lattice Boltzmann Method (LBM). The effective thermal conductivity and viscosity of nanofluid are calculated by the Maxwell–Garnetts (MG) and Brinkman models, respectively. The influence of pertinent parameters such as Hartmann number ( Ha = 0–60), Rayleigh number ( Ra = 10 3 –10 6 ), heat generation or absorption coefficient ( q = − 10, − 5, 0, 5, 10) and nanoparticle volume concentration ( ϕ = 0–0.05) on the flow and heat transfer characteristics has been examined. The results show that the heat transfer increases with an increase of the Rayleigh number and decreases with an increase of the Hartmann number. In addition, the results show that the heat generation or absorption coefficient has a significant effect on the streamlines, isotherms and vortex formation in the enclosure. Moreover, the increase of nanoparticles volume fraction has a positive impact on the average Nusselt number. [ABSTRACT FROM AUTHOR]

Radiative heat transfer is investigated numerically for an industrial combustor of wood carbonization fumes. The combustor has a complex geometry. The finite–volume method (FVM) is applied to study radiative heat transfer in conjunction with the weighted sum of gray gases (WSGG) model of Kim and Song as a non-gray-gas model. The blocked-off-region procedure is applied to treat the geometric irregularities. The reliability of this model, for a complex geometry filled with a semitransparent medium and a regular geometry containing water vapor, is analyzed by comparing its predictions with the exact solution and the Monte Carlo technique associated with the statistical narrow band (SNB) model. Good agreement with benchmarks is found. The extension of this model to a mixture of CO 2 , H 2 O, particles, and soot particles (confined in a complex geometry) is made. The effects of soot volume fraction, partial pressure ratio, particle concentration, and thermal nonequilibrium on the inner wall radiative heat flux of the combustor are presented. [ABSTRACT FROM AUTHOR]

This study aims to numerically investigate the radiation heat transfer in a complex, 3-D biomass pyrolysis reactor which is consisted of two pyrolysis chambers and a heat recuperator. The medium assumes to be gray, absorbs, emits, and Mie-anisotropically scatters the radiation energy. The finite volume method (FVM) is applied to solve the radiation transfer equation (RTE) using the step scheme. To treat the complex geometry, the blocked-off-region procedure is employed. Mie equations (ME) are applied to evaluate the scattering phase function and analyze the angular distribution of the anisotropically scattered radiation by particles. In this study, three different states are considered to test the anisotropic scattering impacts on the temperature and radiation heat flux distribution. These states are as: (i) Isotropic scattering, (ii) forward and backward scattering and (iii) scattering with solid particles of different coals and fly ash. The outcomes demonstrate that the radiation heat flux enhances by an increment of the albedo and absorption coefficients for the coals and fly ash, unlike the isotropic case and the forward and backward scattering functions. Moreover, the particle size parameter does not have an important influence on the radiation heat flux, when the medium is thin optical. Its effect is more noticeable for higher extinction coefficients. [ABSTRACT FROM AUTHOR]