Lattice Boltzmann Modelling of Fluid Flow through Porous Media. A Comparison between Pore-Structure and Representative Elementary Volume Methods

In this study, we present a novel comparison between pore-structure (PS) and representative elementary volume (REV) methods for modelling fluid flow through porous media using a second-order lattice Boltzmann method (LBM). We employ the LBM to demonstrate the importance of the configuration of square obstacles in the PS method and compare the PS and the REV methods. This research provides new insights into fluid flow through porous media as a novel study. The behaviour of fluid flow through porous media has important applications in various engineering structures. The aim of this study is to compare two methods for simulating porous media: the PS method, which resolves the details of the solid matrix, and the REV method, which treats the porous medium as a continuum. Our research methodology involves using different arrangements of square obstacles in a channel including in-line, staggered and random for the PS method and a porosity factor and permeability value for the REV method. We found that the porosity and obstacle arrangement have significant effects on the pressure drop, permeability and flow patterns in the porous region. While the REV method cannot simulate the details of fluid flow through pore structures compared to the PS method, it is able to provide a better understanding of the flow field details around obstacles (Tortuosity). This study has important applications in improving our understanding of transport phenomena in porous media. Our results can be useful for designing and optimizing various engineering systems involving porous media

The Effect of Nanoparticle Shape and Microchannel Geometry on Fluid Flow and Heat Transfer in a Porous Microchannel

Microchannels are widely used in electrical and medical industries to improve the heat transfer of the cooling devices. In this paper, the fluid flow and heat transfer of water–Al2O3 nanofluids (NF) were numerically investigated considering the nanoparticle shape and different cross-sections of a porous microchannel. Spherical, cubic, and cylindrical shapes of the nanoparticle as well as circular, square, and triangular cross-sections of the microchannel were considered in the simulation. The finite volume method and the SIMPLE algorithm have been employed to solve the conservation equations numerically, and the k-ε turbulence model has been used to simulate the turbulence fluid flow. The models were simulated at Reynolds number ranging from 3000 to 9000, the nanoparticle volume fraction ranging from 1 to 3, and a porosity coefficient of 0.7. The results indicate that the average Nusselt number (Nuave) increases and the friction coefficient decreases with an increment in the Re for all cases. In addition, the rate of heat transfer in microchannels with triangular and circular cross-sections is reduced with growing Re values and concentration. The spherical nanoparticle leads to maximum heat transfer in the circular and triangular cross-sections. The heat transfer growth for these two cases are about 102.5% and 162.7%, respectively, which were obtained at a Reynolds number and concentration of 9000 and 3%, respectively. However, in the square cross-section, the maximum heat transfer increment was obtained using cylindrical nanoparticles, and it is equal to 80.2%

Investigation Responses of the Diagrid Structural System of High-rise Buildings Equipped with Tuned Mass Damper Using New Dynamic Method

Due to the shortage of land in cities and population growth, the significance of high rise buildings has risen. Controlling lateral displacement of structures under different loading such as an earthquake is an important issue for designers. One of the best systems is the diagrid method which is built with diagonal elements with no columns for manufacturing tall buildings. In this study, the effect of the distribution of the tuned mass damper (TMD) on the structural responses of diagrid tall buildings was investigated using a new dynamic method. So, a diagrid structural systems with variable height with TMDs was solved as an example of structure. The reason for the selection of the diagrid system was the formation of a stiffness matrix for the diagonal and angular elements. Therefore, the effect of TMDs distribution on the story drift, base shear and structural behaviour were studied. The obtained outcomes showed that the TMDs distribution does not significantly affect on improving the behaviour of the diagrid structural system during an earthquake. Furthermore, the new dynamic scheme represented in this study has good performance for analyzing different systems.

Behaviour Investigation of Sma-Equipped Bar Hysteretic Dampers Using Machine Learning Techniques

Most isolators have numerous displacements due to their low stiffness and damping properties. Accordingly, the supplementary damping systems have vital roles in damping enhancement and lower the isolation system displacement. Nevertheless, in many cases, even by utilising additional dampers in isolation systems, the occurrence of residual displacement is inevitable. To address this issue, in this study, a new smart type of bar hysteretic dampers equipped with shape memory alloy (SMA) bars with recentring features, as the supplementary damper, is introduced and investigated. In this regard, 630 numerical models of SMA-equipped bar hysteretic dampers (SMA-BHDs) were constructed based on experimental samples with different lengths, numbers, and cross sections of SMA bars. Furthermore, by utilising hysteresis curves and the corresponding ideal bilinear curves, the role of geometrical and mechanical parameters in the cyclic behaviour of SMA-BHDs was examined. Due to the deficiency of existing analytical models, proposed previously for steel bar hysteretic dampers (SBHDs), to estimate the first yield point displacement and post-yield stiffness ratio in SMA-BHDs accurately, new models were developed by the artificial neural network (ANN) and group method of data handling (GMDH) approaches. The results showed that, although the ANN models outperform GMDH ones, both ANN-and GMDH-based models can accurately estimate the linear and nonlinear behaviour of SMA-BHDs in pre-and post-yield parts with low errors and high accuracy and consistency

A useful case study to develop lattice Boltzmann method performance: gravity effects on slip velocity and temperature profiles of an air flow inside a microchannel under a constant heat flux boundary condition

Mixed convection heat transfer of air in a 2-D microchannel is investigated numerically by using lattice Boltzmann method. The effects of buoyancy forces on slip velocity and temperature profiles are presented while the microchannel side walls are under a constant heat flux boundary condition. Three states are considered as no gravity, Gr = 100 and Gr = 500. At each state, the value of Knudsen number is chosen as Kn = 0.005, Kn = 0.01 and Kn = 0.02 respectively; while Reynolds number and Prandtl number are kept fixed at Re = 1 and Pr = 0.7. Density-momentum and internal energy distribution functions are used in order to simulate the hydrodynamic and thermal domains in LBM approach. Develop the ability of LBM to simulate the constant heat flux boundary condition along the microchannel walls in the presence of slip velocity and buoyancy forces is proved for the first time at present work. The new and interesting results are achieved such as generating a rotational cell through the fluid flow due to buoyancy forces which leads to see the negative slip velocity at these areas. (C) 2019 Elsevier Ltd. All rights reserved

Thermal Conductivity Enhancement via Synthesis Produces a New Hybrid Mixture Composed of Copper Oxide and Multi-walled Carbon Nanotube Dispersed in Water: Experimental Characterization and Artificial Neural Network Modeling

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Nanofluid is a solid–fluid mixture. By using one solid nanoparticle or one fluid, mono-nanofluid (MN) forms, and by using two solid nanoparticles (NPs) or two fluids, hybrid-nanofluid (HN) forms. For this study, for MN, copper oxide (CuO) and for HN, two solids, which are CuO and multi-walled carbon nanotube (MWCNT) were dispersed in base fluid which is water. After nanofluid preparation, thermal conductivity was measured, and the achievements were numerically modeled. After that, XRD–EDX were performed for the phase-structural analysis. Then, FESEM was examined for NPs-microstructural study. Thermal conductivity (TC) of MN and HN were investigated at 0.2 % to 1.0 % volume fractions (Vf) in 25 °C to 50 °C temperature (T) ranges. Thermal conductivity enhancements of 19.16 % and 37.05 % were seen at the utmost Vf and T for mono-nanofluid and hybrid-nanofluid, respectively. New correlations have been presented with R2 = 0.9, and also Artificial Neural Network (ANN) has been done with R2 = 0.999. For the presented correlation, 0.86 %, and 0.51 % deviations, and for the trained model, 0.41 % and 0.51 % deviations were estimated for mono-nanofluid and hybrid-nanofluid, respectively. As a final result, by adding MWCNT to CuO–H2O mixture, thermal conductivity is raised by 17.89 %, and the hybrid-nanofluid has acceptable heat-transfer capability

THE INFLUENCE OF GRAVITY ON A MICROFLUIDIC MIXED CONVECTION BY APPLYING LATTICE BOLTZMANN METHOD

In this article the effects of gravity on the mixed convection of a microflow is studied numerically by using lattice Boltzmann method (LBM). To do this, the hydrodynamic boundary condition equations should also be modified. The cold fluid enters to the microchannel and leaves it after cooling its hot walls. Calculations are provided for a wide range of Knudsen number (Kn). The results are presented as the isotherms and streamlines, the values of slip velocity and temperature jump and the local and global profiles of velocity, temperature and Nusselt number. It is observed that LBM is able to simulate the mixed convection in a microchannel appropriately. It is claimed that the effects of buoyancy forces are important for Kn0.05 they can be ignored. Moreover, the buoyancy forces make a rotational cell in the microchannel flow which generates the negative slip velocity at Kn=0.005

Develop lattice Boltzmann method and its related boundary conditions models for the benchmark oscillating walls by modifying hydrodynamic and thermal distribution functions

Present works aims to develop the lattice Boltzmann method ability to simulate the periodic supposed problems. Hence, a two-dimensional rectangular enclosure is considered so that its top cold lid oscillates horizontally with time. The stationary sidewalls are kept insulated. It would be necessary to present an appropriate boundary condition model of LBM for the oscillating lid, based on the hydrodynamic and thermal distribution functions. The influences of various lid oscillation frequencies (Strouhal number) are investigated at different values of Richardson numbers at free, mixed and force convections states by using D2Q9 lattice. It is seen that the lid oscillation frequency effect is more significant at less amounts of Richardson number

Increase lattice Boltzmann method ability to simulate slip flow regimes with dispersed CNTs nanoadditives inside: Develop a model to include buoyancy forces in distribution functions of LBM for slip velocity

In this study, the mixed convection of flow in a microchannel containing nanofluid is simulated by the Lattice Boltzmann Method. The water/functionalized multi-wall carbon nanotubes nanofluid is selected as the working fluid. The cold nanofluid passes through the warm walls of the microchannel to cool them down. The buoyancy forces caused by the mass of the nanofluid change the hydrodynamic properties of the flow. Accordingly, the gravitational term is included as an external force in the Boltzmann equation and Boltzmann’s hydrodynamic and thermal equations are rewritten under new conditions. The flow analysis is performed for different values of slip coefficient and Grashof number. The results are expressed in terms of velocity and temperature profiles, contours of streamlines and isotherms beside the slip velocity and temperature jump diagrams. It is observed that the effect of buoyancy force changes the motion properties of the flow in the input region and increases the hydrodynamic input length of flow. These changes are particularly evident at higher values of Grashof numbers and create a rounded circle in the opposite direction of the flow at the microchannel input. The negative slip velocity caused by the vortex resulted in a temperature jump at the input flow region

Impact of ribs on flow parameters and laminar heat transfer of water–aluminum oxide nanofluid with different nanoparticle volume fractions in a three-dimensional rectangular microchannel

This article aims to study the impact of ribs on flow parameters and laminar heat transfer of water–aluminum oxide nanofluid with different nanoparticle volume fractions in a three-dimensional rectangular microchannel. To this aim, compulsory convection heat transfer of water–aluminum oxide nanofluid in a rib-roughened microchannel has been numerically studied. The results of this simulation for rib-roughened three-dimensional microchannel have been evaluated in contrast to the smooth (unribbed) three-dimensional microchannel with identical geometrical and heat–fluid boundary conditions. Numerical simulation is performed for different nanoparticle volume fractions for Reynolds numbers of 10 and 100. Cold fluid entering the microchannel is heated in order to apply constant flux to external surface of the microchannel walls and then leaves it. Given the results, the fluid has a higher heat transfer with a hot wall in surfaces with ribs rather than in smooth ones. As Reynolds number, number of ribs, and nanoparticle volume fractions increase, more temperature increase happens in fluid in exit intersection of the microchannel. By investigating Nusselt number and friction factor, it is observed that increase in nanoparticle volume fractions causes nanofluid heat transfer properties to have a higher heat transfer and friction factor compared to the base fluid used in cooling due to an increase in viscosity