On pore-scale modeling and simulation of reactive transport in 3D geometries

Pore-scale modeling and simulation of reactive flow in porous media has a range of diverse applications, and poses a number of research challenges. It is known that the morphology of a porous medium has significant influence on the local flow rate, which can have a substantial impact on the rate of chemical reactions. While there are a large number of papers and software tools dedicated to simulating either fluid flow in 3D computerized tomography (CT) images or reactive flow using pore-network models, little attention to date has been focused on the pore-scale simulation of sorptive transport in 3D CT images, which is the specific focus of this paper. Here we first present an algorithm for the simulation of such reactive flows directly on images, which is implemented in a sophisticated software package. We then use this software to present numerical results in two resolved geometries, illustrating the importance of pore-scale simulation and the flexibility of our software package.Comment: 15 pages, 6 figure

Improving the Productivity of the E-learning Process

The e-Learning systems have become extremely popular over the last decade. Moreover, not a long time ago they were considered as an alternative way of representing learning content. However, suddenly due to the COVID-19 pandemic they turned out to be the only possible option for keeping the learning process uninterrupted. This makes any research on possible ways of optimizing the presented learning content and its better absorption by the learners, as this paper, extremely important. The paper considers the possibilities for improving the productivity of the e-Learning process in four main areas: (1) reusability of learning content; (2) personalized representation of learning content; (3) proper identification of participants in an e-Learning process; (4) opportunities for easy scaling of learning environments. As a result of the research, a set of methods and models for creating personalized learning materials has been developed. The learning materials are aligned to the learner's preferred learning style and created from a thematicoriented content. All the conceptual models were then implemented into a software environment, which provides an opportunity for their validation and verification and assessment of their effectiveness. The research also presents a so-called "concept for software scaling" from the perspective of an e-Learning environment and a novel software architecture to be used as a base of a system implementation

Numerical Simulation of Frost Formation on a Plate-Fin Evaporator

In the present paper, the Eulerian-granular model is adopted, to predict the frost growth on one channel of a plate-fin evaporator. A proper mass transfer model and modified frosting criteria are used to simulate the frost formation process. First, the model is validated with experimental data obtained under various operating conditions. The numerical predictions for the frost thickness and density are in good agreement with available experimental data. Furthermore, a parametric analysis is carried out to study the impact of the geometrical parameters of a three-dimensional plate-fin evaporator. A qualitative comparison shows a good agreement between the numerical data and experimental observations reported in the literature. One interesting outcome emerging from this study is that the distance between refrigerant tubes can play an important role in the frosting time

On the efficient preconditioning of the Stokes equations in tight geometries

If the Stokes equations are properly discretized, it is well-known that the Schur complement matrix is spectrally equivalent to the identity matrix. Moreover, in the case of simple geometries, it is often observed that most of its eigenvalues are equal to one. These facts form the basis for the famous Uzawa and Krylov-Uzawa algorithms. However, in the case of complex geometries, the Schur complement matrix can become arbitrarily ill-conditioned having a significant portion of non-unit eigenvalues, which makes the established Uzawa preconditioner inefficient. In this article, we study the Schur complement formulation for the staggered finite-difference discretization of the Stokes problem in 3D CT images and synthetic 2D geometries. We numerically investigate the performance of the CG iterative method with the Uzawa and SIMPLE preconditioners and draw several conclusions. First, we show that in the case of low porosity, CG with the SIMPLE preconditioner converges faster to the discrete pressure and provides a more accurate calculation of sample permeability. Second, we show that an increase in the surface-to-volume ratio leads to an increase in the condition number of the Schur complement matrix, while the dependence is inverse for the Schur complement matrix preconditioned with the SIMPLE. As an explanation, we conjecture that the no-slip boundary conditions are the reason for non-unit eigenvalues of the Schur complement

On the structure of the Schur complement matrix for the Stokes equation

In this paper, we investigate the structure of the Schur complement matrix for the fully-staggered finite-difference discretization of the stationary Stokes equation. Specifically, we demonstrate that the structure of the Schur complement matrix depends qualitatively on a particular characteristic, namely the number of non-unit eigenvalues, and the two limiting cases are of special interest

Identification of Channeling in Pore‐Scale Flows

We quantify flow channeling at the microscale in three-dimensional porous media. The study is motivated by the recognition that heterogeneity and connectivity of porous media are key drivers of channeling. While efforts in the characterization of this phenomenon mostly address processes at the continuum scale, it is recognized that pore-scale preferential flow may affect the behavior at larger scales. We consider synthetically generated pore structures and rely on geometrical/topological features of subregions of the pore space where clusters of velocity outliers are found. We relate quantitatively the size of such fast channels, formed by pore bodies and pore throats, to key indicators of preferential flow and anomalous transport. Pore-space spatial correlation provides information beyond just pore size distribution and drives the occurrence of these velocity structures. The latter occupy a larger fraction of the pore-space volume in pore throats than in pore bodies and shrink with increasing flow Reynolds number. Plain Language Summary The movement of fluids and dissolved chemicals through porous media is massively affected by the heterogeneous nature of these systems. The presence of "fast channels," that is, preferential flow paths characterized by large velocities persisting over long distances, gives rise to very short solute travel times, with key implications in, for example, environmental risk assessment. While efforts in the characterization of this phenomenon mostly address processes at the continuum (laboratory or field) scale, it is recognized that pore-scale channeling of flow may affect the system behavior at larger scales. Here we provide criteria for the identification of fast channels at the pore scale, addressing feedback between channeling and geometrical/topological features of the investigated porous structures. Our results clearly evidence the major role of well-defined regions in the pore space, termed pore throats, in driving flow channeling. We also find that the strength of channeling is controlled by the characteristic Reynolds number of the flow field.Fraunhofer Award for Young Researchers; EU; MIUR6 month embargo; published online: 13 March 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

A parallel solver for the design of oil filters

Nowadays, it is widely recognized that computer simulation plays a crucial role in designing oil filters used in the automotive industry. However, even a single direct simulation of the flow usually requires significant computational resources. Thus, it is obvious that solution of optimization problems is only feasible using parallel computers and algorithms.In this paper, we present a general master-slave parallel template, which was specially designed for the easy integration of direct parallel solvers into a parallel optimization tool. We show how an already existing direct solver for the 3D simulation of flow through the oil filter is integrated into our template to obtain a parallel optimization solver. Some capabilities and performance of this solver are demonstrated by solving geometry optimization problem of a filter element