scholarly journals A Model for Coupled Fluid Flow and Multicomponent Chemical Reactions with Application to Sediment Diagenesis

Hydrogeology ◽  
2020 ◽  
pp. 185-203
Author(s):  
Ming-Kuo Lee
Keyword(s):  
Fluid Flow ◽  
Chemical Reactions ◽  
Sediment Diagenesis

Syneresis in Silica Gel

1988 ◽  
Vol 121 ◽  
Author(s):  
George W. Scherer
Keyword(s):  
Fluid Flow ◽  
Sample Size ◽  
Silica Gel ◽  
Chemical Reactions ◽  
Driving Force ◽  
Viscoelastic Behavior ◽  
Accurate Representation ◽  
Flow Through ◽  
Kinetics Of ◽  
Gel Network

ABSTRACTThe driving force for syneresis is generally attributed to the same chemical reactions that produce gelation, but it has also been proposed that shrinkage could be driven by interracial energy. The latter possibility is explored and discounted. The kinetics of syneresis depend on the driving force, the mobility of the gel network, and the rate of fluid flow through the contracting gel. A model that allows for viscoelastic behavior of the gel and fluid flow according to Darcy's law is shown to provide a quantitatively accurate representation of the shape of the shrinkage curves and the dependence of the shrinkage rate on sample size.

scholarly journals Modeling Validation and Simulation of an Anode Supported SOFC Including Mass and Heat Transport, Fluid Flow and Chemical Reactions

2011 ◽  
Author(s):  
Martin Andersson ◽  
Jinliang Yuan ◽  
Bengt Sunde´n ◽  
Ting Shuai Li ◽  
Wei Guo Wang
Keyword(s):  
Fluid Flow ◽  
Chemical Reactions ◽  
Reaction Rates ◽  
Operating Conditions ◽  
Material Structure ◽  
Internal Reforming ◽  
Transport Distance ◽  
Lack Of Information ◽  
Partial Pressures ◽  
Temperature Standard

Fuel cells are electrochemical devices that directly transform chemical energy into electricity, which are promising for future energy systems, since they are energy efficient and, when hydrogen is used as fuel, there are no direct emissions of greenhouse gases. The cell performance depends strongly on the material characteristics, the operating conditions and the chemical reactions that occur inside the cell. The chemical- and electrochemical reaction rates depend on temperature, material structure, catalytic activity, degradation and the partial pressures for the different species components. There is a lack of information, within the open literature, concerning the fundamentals behind these reactions. Experimental as well as modeling studies are needed to reduce this gap. In this study experimental data collected from an intermediate temperature standard SOFC with H2/H2O in the fuel stream are used to validate a previously developed computational fluid dynamics model based on the finite element method. The developed model is based on the governing equations of heat and mass transport and fluid flow, which are solved together with kinetic expressions for internal reforming reactions of hydrocarbon fuels and electrochemistry. This model is further updated to describe the experimental environment concerning cell design. Discussion on available active area for electrochemical reactions and average ionic transport distance from the anodic- to the cathodic three-phase boundary (TPB) are presented. The fuel inlet mole fractions are changed for the validated model to simulate a H2/H2O mixture and 30% pre-reformed natural gas.

On the constitutive equations for coupled chemical reaction and deformation of porous rocks

2021 ◽  
Author(s):  
Yury Podladchikov ◽  
Viktoriya Yarushina ◽  
Benjamin Malvoisin
Keyword(s):  
Fluid Flow ◽  
Chemical Reactions ◽  
Constitutive Equations ◽  
Reactive Transport ◽  
Coupled Processes ◽  
Stable Phase ◽  
Precipitation Process ◽  
Porous Rocks ◽  
Mineral Growth ◽  
Reactive Surfaces

<p>Deformation, chemical reactions, and fluid flow in the geological materials are coupled processes. While some reactions are thought to be a consequence of fluid assisted dissolution on the stressed mineral surfaces and precipitation on the free surface, other reactions are caused by mineral replacement wherein a less stable mineral phase is replaced by a more stable phase, involving a change in solid volume and build-up of stresses on grain contacts, also known as a force of crystallization. Most of the existing models of chemical reactions coupled with fluid transport either assume dissolution-precipitation process or mineral growth in rocks. However, dissolution-precipitation models used together with fluid flow modelling predict a very limited extent of reaction hampered by pore clogging and blocking of reactive surfaces, which will stop reaction progress due to the limited supply of fluid to reactive surfaces. Yet, field observations report that natural rocks can undergo 100% hydration/carbonation. Mineral growth models, on the other hand, preserve solid volume but do not consider its feedback on porosity evolution. In addition, they predict the unrealistically high force of crystallization on the order of several GPa that must be developed in minerals during the reaction. Here, using a combination of effective media theory and irreversible thermodynamics approaches, we propose a new model for reaction-driven mineral expansion, which preserves porosity and limits unrealistically high build-up of the force of crystallization by allowing inelastic failure processes at the pore scale. To fully account for the coupling between reaction, deformation, and fluid flow we derive macroscopic poroviscoelastic stress-strain constitute laws, that account for chemical alteration and viscoleastic deformation of porous rocks. These constitutive equations are then used to simulate the reactive transport in porous rocks.</p>

scholarly journals Simulation of a thermoelectric gas sensor that determines hydrocarbon concentrations in exhausts and the light-off temperature of catalyst materials

2017 ◽  
Vol 6 (2) ◽  
pp. 395-405 ◽  
Author(s):  
Thomas Ritter ◽  
Sven Wiegärtner ◽  
Gunter Hagen ◽  
Ralf Moos
Keyword(s):  
Fluid Flow ◽  
Gas Sensor ◽  
Chemical Reactions ◽  
Catalyst Layer ◽  
Gas Diffusion ◽  
Transient Temperature ◽  
Temperature Modulation ◽  
Offset Voltage ◽  
Stationary Conditions ◽  
Sensor Temperature

Abstract. Catalyst materials can be characterized with a thermoelectric gas sensor. Screen-printed thermopiles measure the temperature difference between an inert part of the planar sensor and a part that is coated with the catalyst material to be analyzed. If the overall sensor temperature is modulated, the catalytic activity of the material can be varied. Exothermic reactions that occur at the catalyst layer cause a temperature increase that can then be measured as a sensor voltage due to the Seebeck coefficient of the thermopiles. This mechanism can also be employed at stationary conditions at constant sensor temperature to measure gas concentrations. Then, the sensor signal changes linearly with the analyte concentration. Many variables influence the sensing performance, for example, the offset voltage due to asymmetric inflow and the resulting inhomogeneous temperature distributions are an issue. For even better understanding of the whole sensing principle, it is simulated in this study by a 3-D finite element model. By coupling all influencing physical effects (fluid flow, gas diffusion, heat transfer, chemical reactions, and electrical properties) a model was set up that is able to mirror the sensor behavior precisely, as the comparison with experimental data shows. A challenging task was to mesh the geometry due to scaling problems regarding the resolution of the thin catalyst layer in the much larger gas tube. Therefore, a coupling of a 3-D and a 1-D geometry is shown. This enables to calculate the overall temperature distribution, fluid flow, and gas concentration distribution in the 3-D model, while a very accurate calculation of the chemical reactions is possible in a 1-D dimension. This work does not only give insight into the results at stationary conditions for varying feed gas concentrations and used substrate materials but shows also how various exhaust gas species behave under transient temperature modulation.

Coupled fluid flow and chemical reactions in unsaturated pyrite tailings

2007 ◽  
Author(s):  
S Olivella ◽  
C Ayora ◽  
P Acero ◽  
J Nieto ◽  
J Carrera ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Chemical Reactions ◽  
Pyrite Tailings
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