Percolation thresholds for discrete-continuous models with nonuniform probabilities of bond formation

We introduce a class of discrete-continuous percolation models and an efficient Monte Carlo algorithm for computing their properties. The class is general enough to include well-known discrete and continuous models as special cases. We focus on a particular example of such a model, a nanotube model of disintegration of activated carbon. We calculate its exact critical threshold in two dimensions and obtain a Monte Carlo estimate in three dimensions. Furthermore, we use this example to analyze and characterize the efficiency of our algorithm, by computing critical exponents and properties, finding that it compares favorably to well-known algorithms for simpler systems. © 2016 American Physical Society.This work has been partially supported by the Iuventus Plus programme founded by the Polish Ministry of Science and Higher Education (IP2014 024373). M.L. acknowledges Spanish MINECO Project FOQUS (FIS2013-46768), ERC AdG OSYRIS, EU IP SIQS, EU STREPEQuaM, and EU FETPROACT QUIC. J.W. has been partially funded by NSF grant DMS 131271.Peer reviewe

OpenFOAM solver for thermal and chemical conversion in porous media

We present the porousGasificationFoam solver and libraries, developed in the open-source C++ code OpenFOAM, for the comprehensive simulation of the thermochemical conversion in porous media. The code porousGasificationFoam integrates gas flow through a porous media with the models of heterogeneous (drying, gasification, pyrolysis, solid combustion, precipitation) and homogeneous (gas combustion) chemical reactions. Inside porous media transport equations are formulated applying the spatial averaging methodology. The mass and enthalpy transfer between solid and gas phases is suitable for systems out of the thermal equilibrium. The convection and radiation modes of the heat transfer are included for gas and solid phases, and the immersed boundary technique is applied for the porous media inside the computational domain. We validate the elements of the model against a set of experimental and theoretical results. Amongst them, Thermogravimetric Analysis experiments of thermal conversions of two wooden particles: one of millimeter size the other of centimeter size. Simulations feature reaction schemes and physical parameters established in the literature. We show the influence of the porous media size on the gasification process. The millimeter particle remains uniform, while for the centimeter setup, the pyrolysis front is reproduced. The spatial patterns in physical conditions modify the course of chemical reactions and influence media composition and structure evolution. Another important example is a gasifier where we obtain a self-sustaining front propagation due to an exothermic heterogeneous reaction. Program summary Program Title: porousGasificationFoam CPC Library link to program files: https://doi.org/10.17632/s6sj9kgp69.1 Developer's repository link: https://github.com/pjzuk/porousGasificationFoam(foam-extend-4.1); https://github.com/btuznik/porousGasificationFoam(OpenFOAM 8) Licensing provisions: GNU General Public Licence version 3 Programming language: C++ External routines/libraries: OpenFOAM 8, foam-extend-4.1 Nature of problem: The developed software is a solver and a set of libraries for simulating the thermal conversion in porous media, including drying, pyrolysis, gasification, and combustion. The model includes the flow of the reactive gas mixture and the transfer of mass and enthalpy between the gas and solid phases. The porous medium can change during the process. The model is transient and enables three-dimensional simulations.Solution method: The finite-volume method is used in the code for equation discretization. A set of governing equations is solved for the gas and solid phases, including mass conservation of gas species and solid components, momentum conservation in the gas phase, and equations of enthalpy conservation in both phases. The porous media region inside the whole computational domain is defined using the immersed boundary approach