Papers by Keyword: Lattice Boltzmann Method

Abstract: This article reports the transient solution of a one-dimensional (1-D) heat conduction problem having temperature-dependent internal heat generation in a slab. The slab is assumed to be made of a homogeneous material with constant thermal properties. Furthermore, the boundary conditions at two extremities of the slab are considered to be suddenly imposed temperature and convective heat transfer respectively. The present investigation emphasizes the occurrence of non-linear internal heat generation within material owing to the presence of absorption phenomenon, exothermic reaction, and flow of electrons which can be foreseen in the application of hot wire anemometer, optoelectrical arrangement, etc. Lattice Boltzmann (LB) method has been effectively implemented for obtaining the solution of a non-linear governing differential equation. The investigation outcomes would be informative to the designer in the field of transient analysis of one-dimensional slabs associated with heat generation.

Abstract: The gas diffusion layer (GDL) is a crucial component of Proton Exchange Membrane Fuel Cells (PEMFC), water flooding will occur during the operation of PEMFC, resulting in performance degradation, and its water management plays a significant role in PEMFC performance. To investigate the transport mechanism of liquid water in GDL, the lattice Boltzmann method to simulate the behavior of GDL droplets using the 'random reconstruction' method. The accuracy of this model by calculating the tortuosity and comparing it with reported results in literature. The effects of different GDL structural parameters on permeability were studied. Finally, the conductivity and thermal conductivity of the GDL in various directions were examined. The results indicate that the porosity error of the three-dimensional structure model of GDL is within 0.01, enabling a realistic simulation of the GDL structure. The average error between the calculated results and the Bruggeman equation is only 2.5362%, and the average error compared to the reference results is less than 6%, demonstrating the model's high accuracy. As the porosity and fiber diameter of the GDL three-dimensional structure model increase, the permeability also increases. Conversely, the permeability decreases with an increase in the thickness of the GDL three-dimensional structure model. Moreover, an increase in GDL porosity leads to a gradual decrease in electrical conductivity and thermal conductivity in both the thickness and plane directions, with a more pronounced effect on the thickness. This study uncovers the transport characteristics of liquid water in the gas diffusion layer, which can inform the optimization of GDL structure design and serve as a theoretical reference for enhancing water management in proton exchange membrane fuel cells. Future research directions will focus on further optimizing the three-dimensional structure of GDL to improve its transmission characteristics and overall performance.

Abstract: To gain better understanding of rheological transitions from suspension flow to granular deformation and shear cracking, this research conducted shear-deformation on globular semi-solid Al-Cu alloys to study the rheological behavior of semi-solid as a function of solid fraction (38% - 85%) and shear rate (10^-4 – 10^-1 s^-1) under real-time synchrotron radiography observation. By analyzing 17 X-ray imaging datasets, we define three rheological transitions: (i) the critical solid fraction from a suspension to a loosely percolating assembly; (ii) from the net contraction of a loose assembly to the net dilation of a densely packed assembly, and (iii) to shear cracking at high solid fraction and shear rate. Inspired by in-situ observations of semi-solid deformation showing a disordered assembly of percolating crystals in partially-cohesive contact with liquid flow, we reproduced a two-phase sample using the coupled lattice Boltzmann method-discrete element method (LBM-DEM) simulation approach for granular micromechanical modeling. In DEM, each globular Al grain is represented by a discrete element, and the flow of interstitial liquid is solved by LBM. The LBM-DEM simulations show quantitative agreement of semi-solid strain localization with the experiments and are used to explore the components involved in the shear rate dependence of the transitions, and the role of liquid pressure on the initiation of shear cracking.

Abstract: We present in this work a numerical study of a ventilation system in a room with two openings in the ceiling and a floor heating indicated by constant heat temperature. The double population thermal lattice Boltzmann method is used, with nine velocities model D2Q9 for the dynamic field and a five velocities model D2Q5 for the temperature field. The results are presented in the form of streamlines, temperature contour and velocity profile, and analysed as a function of the Richardson number.

Abstract: In the present numerical study, the convection diffusion phenomena associated with solid-liquid phase transition processes during phase change material (PCM) melting within a rectangular cavity is studied. The cavity is heated from left wall with a sinusoidal temperature distribution. Initially the enclosure was filled by solid gallium at melting temperature 29.78°C. The enthalpy-based lattice Boltzmann method (LBM) with D2Q9 particle velocity model is used to solve density, velocity and temperature fields. Influence of Rayleigh number ranging from 10³ to 4×10⁵ on streamlines, isotherms and liquid fraction is analyzed. The results indicate that natural convection of liquid phase change material (PCM) plays a significant role in the melting heat transfer of PCM. It is found that the rate of the melting increases with the increase in the values of the Rayleigh number.

Abstract: Multilayered laminate structures obtained by coating of ultrafine-grained metallic materials with bioactive and multifunctional composite coatings are considered for biomedical applications. Laser-assisted densification of multiple materials using laser cladding and selective laser melting is an alternative route to reduce the risk of early implant failure allowing for faster and cheaper fabrication. To understand the cooperative relationships between different factors that cam influence the manufacture of such bioactive laminates reflecting in their bioactivity and mechanical properties, the multi scale numerical modelling is applied. This work presents resent advances on development of integrated numerical models including generation, melting and solidification of the powder bed, considering surface flow, wettability, surface tension and other physical phenomena, specific mechanical and thermo-mechanical aspects and microstructure evolution.

Abstract: The work in this manuscript deals with the numerical simulation of natural convection in a staggered cavity with the help of a recently developed two-dimensional double Multiple-Relaxation-Time (MRT) thermal Lattice Boltzmann method (LBM). In the last decade, there has been a rapid rise in the development of Lattice Boltzmann methods. However, its application in the simulation of natural convection from a staggered cavity has been carried out for the first time in this study. A careful undermining into the existing literature of heat and mass transfer reveal that study of natural convections in cross-sectional cavities is notably absent. Therefore, in this manuscript, we attempt to review the recently developed method and tried to analyze its implementation on natural convection in a staggered cavity with four differentially heated vertical walls. The problem geometry has eight boundaries. It is a staggered cavity with adiabatic horizontal walls and differentially heated vertical walls. The flow inside the thermally driven staggered cavity has been carefully studied for Rayleigh numbers 10³, 10⁴ and 10⁵. The velocity and pressure boundary conditions are determined by a non-equilibrium extrapolation rule. As no benchmark results are available in the literature for this relatively new problem, we carry out its simulation with the help of a yet another well established scheme. This scheme is a higher-order compact (HOC) scheme with fourth order spatial accuracy and second order temporal accuracy. Our results show that there is a very good agreement between both these methods which exemplifies the accuracy and credibility of our results.

Abstract: The main objective of this work is to develop a new approach based on the Lattice Boltzmann method (LBM) to simulate the extrudate swell of an Oldroyd B viscoelatic fluid. Two lattice Boltzmann equations are used to solve the Navier-Stokes equations and constitutive equation simultaneously at each time iteration. The single LBM model is used to track the moving interface in this paper. To validate the accuracy and stability of this new scheme, we study the steady 2D Poiseuille flow firstly, finding the numerical results be in good accord with the analytical solution. Then the die-swell phenomenon is solved, we successfully acquire the different swelling state of an Oldroyd B fluid at different time.

Abstract: The effective thermal conductivity is an important parameter used to predict the thermal performance analysis of complex structured porous building materials. The observation of porous structure of building materials on REV (representative elementary volume) scale showed that pores can be classified into meso and macro pores. In contrast to the traditional models usually used for the (macro-meso) pore connection , a new numerical random generation macro-meso pores (RGMMP) method, based on geometrical and morphological information acquired from measurements or experimental calculations, is proposed here. Along with proposed structure generating tool RGMMP a high efficiency LBM, characterized with the energy conservation and appropriate boundary conditions at numerous interfaces in the complex system, for the solution of the governing equation is described which yields a powerful numerical tool to obtain accurate solutions. Then present model is validated with some theoretical and experimental values of effective thermal conductivity of typical building materials. The comparison of present model and experimental results shows that the proposed model agrees much better with the experimental data than the traditional theoretical models. Therefore, the present model is not limited to the described building materials but can also be used for predicting the effective thermal conductivity of any type of complex structured building materials.

Abstract: Ultra-fast laser heating technology has been widely used in the micro-/nanodevices. The Lattice Boltzmann method (LBM) is employed to simulate the heat conductions of laser heating appeared in a thin film. The results obtained by the LBM show that a wavelike behavior is appeared, but it can not be found in Fourier prediction. Comparing the results obtained by the Fourier law and LBM, we find that the LBM solution shows higher temperature than the Fourier prediction. Moreover, simultaneously heating both surfaces of a thin silicon film by ultra-fast lasers can induce two thermal waves traveling in the opposite directions, and when they meet together, the energy will enhance significantly.