scholarly journals Fundamental Numerical Analysis of a Porous Micro-Combustor Filled with Alumina Spheres: Pore-Scale vs. Volume-Averaged Models

2021 ◽  
Vol 11 (16) ◽  
pp. 7496
Author(s):  
Qingqing Li ◽  
Jiansheng Wang ◽  
Jun Li ◽  
Junrui Shi
Keyword(s):  
Porous Media ◽  
Flame Temperature ◽  
Scale Model ◽  
Solid Matrix ◽  
Flame Stability ◽  
Pore Scale ◽  
Flame Zone ◽  
Heat Recirculation ◽  
Micro Combustor ◽  
Averaged Model

Inserting porous media into the micro-scale combustor space could enhance heat recirculation from the flame zone, and could thus extend the flammability limits and improve flame stability. In the context of porous micro-combustors, the pore size is comparable to the combustor characteristic length. It is insufficient to treat the porous medium as a continuum with the volume-averaged model (VAM). Therefore, a pore-scale model (PSM) is developed to consider the detailed structure of the porous media to better understand the coupling among the gas mixture, the porous media and the combustor wall. The results are systematically compared to investigate the difference in combustion characteristics and flame stability limits. A quantified study is undertaken to examine heat recirculation, including preheating and heat loss, in the porous micro-combustor using the VAM and PSM, which are beneficial for understanding the modeled differences in temperature distribution. The numerical results indicate that PSM predicts a scattered flame zone in the pore areas and gives a larger flame stability range, a lower flame temperature and peak solid matrix temperature, a higher peak wall temperature and a larger Rp-hl than a VAM counterpart. A parametric study is subsequently carried out to examine the effects of solid matrix thermal conductivity (ks) on the PSM and VAM, and then the results are analyzed briefly. It is found that for the specific configurations of porous micro-combustor considered in the present study, the PSM porous micro-combustor is more suitable for simplifying to a VAM with a larger Φ and a smaller ks, and the methods can be applied to other configurations of porous micro-combustors.

A Predictive Pore-Scale Model for Non-Darcy Flow in Porous Media

SPE Journal ◽  
2009 ◽  
Vol 14 (04) ◽  
pp. 579-587 ◽  
Author(s):  
Matthew T. Balhoff ◽  
Mary F. Wheeler
Keyword(s):  
Porous Media ◽  
Darcy Flow ◽  
Flow In Porous Media ◽  
Scale Model ◽  
Pore Scale ◽  
Pore Scale Model

scholarly journals A numerical study on oxygen adsorption in porous media of coal rock based on fractal geometry

2020 ◽  
Vol 7 (2) ◽  
pp. 191337
Author(s):  
Xianzhe Lv ◽  
Xiaoyu Liang ◽  
Peng Xu ◽  
Linya Chen
Keyword(s):  
Porous Media ◽  
Scaling Laws ◽  
Spontaneous Combustion ◽  
Numerical Study ◽  
Nitrogen Adsorption ◽  
Oxygen Adsorption ◽  
Scale Model ◽  
Pore Scale ◽  
Coal Rock ◽  
Pore Scale Model

In order to explore the factors affecting coal spontaneous combustion, the fractal characteristics of coal samples are tested, and a pore-scale model for oxygen adsorption in coal porous media is developed based on self-similar fractal model. The liquid nitrogen adsorption experiments show that the coal samples indicate evident fractal scaling laws at both low-pressure and high-pressure sections, and the fractal dimensions, respectively, represent surface morphology and pore structure of coal rock. The pore-scale model has been validated by comparing with available experimental data and numerical simulation. The present numerical results indicate that the oxygen adsorption depends on both the pore structures and temperature of coal rock. The oxygen adsorption increases with increased porosity, fractal dimension and ratio of minimum to maximum pore sizes. The edge effect can be clearly seen near the cavity/pore, where the oxygen concentration is low. The correlation between the oxygen adsorption and temperature is found to obey Langmuir adsorption theory, and a new formula for oxygen adsorption and porosity is proposed. This study may help understanding the mechanisms of oxygen adsorption and accordingly provide guidelines to lower the risk of spontaneous combustion of coal.

scholarly journals Numerical Simulation on Hydromechanical Coupling in Porous Media Adopting Three-Dimensional Pore-Scale Model

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Jianjun Liu ◽  
Rui Song ◽  
Mengmeng Cui
Keyword(s):  
Finite Element ◽  
Porous Media ◽  
Pore Pressure ◽  
Three Dimensional ◽  
Confining Pressure ◽  
Scale Model ◽  
Micro Ct ◽  
Pore Scale ◽  
Hydromechanical Coupling ◽  
Rock Matrix

A novel approach of simulating hydromechanical coupling in pore-scale models of porous media is presented in this paper. Parameters of the sandstone samples, such as the stress-strain curve, Poisson’s ratio, and permeability under different pore pressure and confining pressure, are tested in laboratory scale. The micro-CT scanner is employed to scan the samples for three-dimensional images, as input to construct the model. Accordingly, four physical models possessing the same pore and rock matrix characteristics as the natural sandstones are developed. Based on the micro-CT images, the three-dimensional finite element models of both rock matrix and pore space are established by MIMICS and ICEM software platform. Navier-Stokes equation and elastic constitutive equation are used as the mathematical model for simulation. A hydromechanical coupling analysis in pore-scale finite element model of porous media is simulated by ANSYS and CFX software. Hereby, permeability of sandstone samples under different pore pressure and confining pressure has been predicted. The simulation results agree well with the benchmark data. Through reproducing its stress state underground, the prediction accuracy of the porous rock permeability in pore-scale simulation is promoted. Consequently, the effects of pore pressure and confining pressure on permeability are revealed from the microscopic view.

scholarly journals A macroscopic two-length-scale model for natural convection in porous media driven by a species-concentration gradient

2021 ◽  
Vol 926 ◽  
Author(s):  
Stefan Gasow ◽  
Andrey V. Kuznetsov ◽  
Marc Avila ◽  
Yan Jin
Keyword(s):  
Porous Media ◽  
Natural Convection ◽  
Sherwood Number ◽  
Darcy Number ◽  
Scale Model ◽  
Length Scale ◽  
Pore Scale ◽  
Diffusion Term ◽  
Engineering Problems ◽  
Convection In Porous Media

The modelling of natural convection in porous media is receiving increased interest due to its significance in environmental and engineering problems. State-of-the-art simulations are based on the classic macroscopic Darcy–Oberbeck–Boussinesq (DOB) equations, which are widely accepted to capture the underlying physics of convection in porous media provided the Darcy number, $Da$ , is small. In this paper we analyse and extend the recent pore-resolved direct numerical simulations (DNS) of Gasow et al. (J. Fluid Mech, vol. 891, 2020, p. A25) and show that the macroscopic diffusion, which is neglected in DOB, is of the same order (with respect to $Da$ ) as the buoyancy force and the Darcy drag. Consequently, the macroscopic diffusion must be modelled even if the value of $Da$ is small. We propose a ‘two-length-scale diffusion’ model, in which the effect of the pore scale on the momentum transport is approximated with a macroscopic diffusion term. This term is determined by both the macroscopic length scale and the pore scale. It includes a transport coefficient that solely depends on the pore-scale geometry. Simulations of our model render a more accurate Sherwood number, root mean square (r.m.s.) of the mass concentration and r.m.s. of the velocity than simulations that employ the DOB equations. In particular, we find that the Sherwood number $Sh$ increases with decreasing porosity and with increasing Schmidt number $(Sc)$ . In addition, for high values of $Ra$ and high porosities, $Sh$ scales nonlinearly. These trends agree with the DNS, but are not captured in the DOB simulations.

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