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In this work, we present an extension of the lattice Boltzmann method for solving radiative transfer equation (RTE) in emitting, absorbing, and non-scattering gaseous mixtures produced by combustion. A numerical procedure based on LBM is first developed for a single absorption coefficient avoiding spectral effect (gray gas model). Therefore, an infrared radiative global model is associated with the LBM to assess the radiative heat exchanges in molecular gaseous mixtures. A global model based on absorption distribution function (ADF) and a D2Q16 scheme are implemented to solve the 2D RTE. Results are presented in terms of temperature, radiative heat flux, and volumetric radiative power. Effects of radiative behavior and spectral structure of gaseous mixtures are put in evidence. The application of the LBM-ADF8 to gaseous mixture produced by combustion emphasizes the importance of taking into account its spectral structures. The error induced by the gray media approximation is put in evidence. [ABSTRACT FROM AUTHOR]

In this study, the lattice Boltzmann method is utilized to investigate the effects of porous medium at the exit of the counterflow combustion. Porous matrices with different arrangements are created by scattering solid obstacles inside the flow path. The LBM model is used for simulation of conduction heat transfer between the discrete parts of the porous medium. A single-step chemical reaction is used for modeling of the combustion of propane/air mixture and properties are recorded at the exit of the domain. However, to investigate the effects of porous media on the emission of the intermediate species like CO, a two-step chemical reaction is utilized to model the methane/air combustion. The results show that the presence of the porous media decreases the maximum exit temperature and causes a more uniform temperature profile at the exit compared with results of combustion without porous medium. Also, utilizing porous media reduces the CO and unburned fuel concentration at the exit and consequently increases the combustion efficiency. Effects of the different porous structure on exit temperature and species concentrations are also investigated in this study. [ABSTRACT FROM AUTHOR]

Abstract: Effect of static radial magnetic field on natural convection heat transfer in a horizontal cylindrical annulus enclosure filled with nanofluid is investigated numerically using the Lattice Boltzmann method (LBM). The inner and outer cylinder surfaces are maintained at the different uniform temperatures. The surfaces are non-magnetic material. The investigation is carried out for different governing parameters namely, Hartmann number, nanoparticle volume fraction and Rayleigh number. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. The results reveal that the flow oscillations can be suppressed effectively by imposing an external radial magnetic field. Also, it is found that the average Nusselt number is an increasing function of nanoparticle volume fraction and Rayleigh number, while it is a decreasing function of Hartmann number. [Copyright &y& Elsevier]

The lattice Boltzmann method (LBM) has two key steps: collision and streaming. In a conventional LBM, the streaming is exact, where each distribution function is perfectly shifted to the neighbor node on the uniform mesh arrangement. This advantage may curtail the applicability of the method to problems with complex geometries. To overcome this issue, a high-order meshless interpolation-based approach is proposed to handle the streaming step. Owing to its high accuracy, the radial basis function (RBF) is one of the popular methods used for interpolation. In general, RBF-based approaches suffer from some stability issues, where their stability strongly depends on the shape parameter of the RBF. In the current work, a stabilized RBF approach is used to handle the streaming. The stabilized RBF approach has a weak dependency on the shape parameter, which improves the stability of the method and reduces the dependency of the shape parameter. Both the stabilized RBF method and the streaming of the LBM are used for solving three benchmark problems. The results of the stabilized method and the perfect streaming LBM are compared with analytical solutions or published results. Excellent agreements are observed, with a little advantage for the stabilized approach. Additionally, the computational cost is compared, where a marginal difference is observed in the favor of the streaming of the LBM. In conclusion, one could report that the stabilized method is a viable alternative to the streaming of the LBM in handling both simple and complex geometries. [ABSTRACT FROM AUTHOR]

Abstract Removal of the condensed liquid from a micro-object and controlling the surface wettability in multiphase flows are important for many industrial applications. To achieve these goals, a rotating shell is used around a micro-square cylinder. Lattice Boltzmann method is used to simulate the process. The behaviors of the liquid condensed on the micro-cylinder together with the liquid breakup and liquid trajectory after separation are studied for different values of shell turning velocities. The results indicated that the separation speed increases and the breakup time decreases with increasing the rotation speed of the conveyor. For the rotation speed of 0.05 Lu/ts, the initial breakup time was 7312 ts. However, the initial breakup times reduce to about 74.6% and 82.06% with increasing the rotation speed in the ranges 0.05 Lu/ts to 0.1 Lu/ts and 0.05 Lu/ts to 0.125 Lu/ts, respectively. Highlights • Removal of the condensed liquid from a micro-object is investigated. • Rotating shell is used around micro-square cylinder to control surface wettability. • Lattice Boltzmann method is used to simulate the process. • The separation speed increases with increasing the rotation speed of the conveyor. • The breakup time decreases with increasing the rotation speed of the conveyor. [ABSTRACT FROM AUTHOR]

The nanoparticles in fluid enhance the rate of heat transfer because of higher thermal conductivity of nanoparticles. In literature, researchers have used different numerical methods to simulate this phenomenon considering the fluid as a single phase or as a two phase system. In some cases, the numerical results were compared with experimental results and good agreements were achieved; while for other no comparison was done. On the other hand, there is no identical numerical research that compares various numerical approaches that can be used to study thermo-fluidic flow in nanofluid. Accordingly, in this study we have numerically solved a benchmark heat transfer nanofluid problem using three different widely used numerical approaches: Finite Element Method (FEM), Lattice Boltzmann Method (LBM) and Finite Difference Method (FDM). The numerical results were compared with experimental results in literature for validation purposes. Subsequently, a FEM simulation is carried out for a three dimensional domain to investigate the three dimensional effects of the enclosure’s walls on heat transfer in the nanofluid. The simulations were performed for water (H 2 O)-aluminum oxide(Al 2 O 3 ) nanofluid at a particle concentration range of 1%–3% volume fraction. Numerical results in the forms of temperature, stream function and velocity variations as well as average Nusselt number at the walls have been presented for a range of Rayleigh numbers (for different particles concentration). While, a suitable combination of the governing control parameters resulted in an acceptable CFD outcomes for all three numerical methods, some differences have been observed between different numerical approaches which are reported in this study. Eventually, the strength and weakness of various numerical approaches are discussed in details. [ABSTRACT FROM AUTHOR]

In this paper, the two-dimensional forced convection heat transfer of non-Newtonian power-law fluid flow between two parallel plates filled with partially porous media is studied numerically using the thermal lattice Boltzmann method (TLBM). Shear-thinning (n=0.8), Newtonian (n=1.0), and shear-thickening (n=1.2) fluid are used to investigate the non-Newtonian behavior of power-law fluids. The porous media is prepared by the arrangement of circular obstacles. The effect of Reynolds numbers between 100

Numerical investigation of bubbly flow throughout an anisotropic porous medium and the related two-phase phenomena is carried out, to provide a profound insight into the probabilities of transmitting or accumulating vapor bubbles within porous structures. The lattice Boltzmann method is used in the analysis. The effects of different flow regimes, contact angles, and porosity on a single rising bubble dynamic within a porous medium are assessed. The probability of different scenarios such as pinch-off, vapor jacket or vapor blanket at different flow regimes and conditions are considered of multiple rising bubbles. Generally, obstruction, coalescence, separation and deformation of vapor bubbles are claimed to be tightly dependent on the interaction of buoyancy, adhesion, drag and surface tension. Also, it is found that at high Eotvos (EO) number, the porous medium shows a little tendency to transmit the vapor bubbles, while at the moderate EO number, especially with aerophobic walls, the bubbles pass through the porous medium without any disturbance. Besides, the low EO number is claimed to be an inappropriate condition because of the presence of accumulated vapor bubbles within the porous medium, which is well-known as a vapor blanket phenomenon. • Buoyancy-driven vapor bubbles throughout a porous media at pore-scale are studied. • Multiphase phenomena of vapor are illustrated within an anisotropic porous medium. • For aerophobic surfaces drag force during obstruction are not effective. • The porous medium has the highest transmitted performance of bubbles at low EO number. • In the high EO number, the bubble can deform and move within the obstacle. [ABSTRACT FROM AUTHOR]