02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
Browse
4 results
Search Results
Item Open Access Estimation of capillary‐associated NAPL‐water interfacial areas for unconsolidated porous media by kinetic interface sensitive (KIS) tracer method(2023) Tatomir, Alexandru; Gao, Huhao; Abdullah, Hiwa; Pötzl, Christopher; Karadimitriou, Nikolaos; Steeb, Holger; Licha, Tobias; Class, Holger; Helmig, Rainer; Sauter, MartinBy employing kinetic interface sensitive (KIS) tracers, we investigate three different types of glass‐bead materials and three natural porous media systems to quantitatively characterize the influence of the porous‐medium grain‐, pore‐size and texture on the specific capillary‐associated interfacial area (FIFA) between an organic liquid and water. By interpreting the breakthrough curves (BTCs) of the reaction product of the KIS tracer hydrolysis, we obtain a relation for the specific IFA and wetting phase saturation. The immiscible displacement process coupled with the reactive tracer transport across the fluid-fluid interface is simulated with a Darcy‐scale numerical model. Linear relations between the specific capillary‐associated FIFA and the inverse mean grain diameter can be established for measurements with glass beads and natural soils. We find that the grain size has minimal effect on the capillary‐associated FIFA for unconsolidated porous media formed by glass beads. Conversely, for unconsolidated porous media formed by natural soils, the capillary‐associated FIFA linearly increases with the inverse mean grain diameter, and it is much larger than that from glass beads. This indicates that the surface roughness and the irregular shape of the grains can cause the capillary‐associated FIFA to increase. The results are also compared with the data collected from literature, measured with high resolution microtomography and partitioning tracer methods. Our study considerably expands the applicability range of the KIS tracers and enhances the confidence in the robustness of the method.Item Open Access Experimental methods and imaging for enzymatically induced calcite precipitation in a microfluidic cell(2021) Weinhardt, Felix; Class, Holger; Vahid Dastjerdi, Samaneh; Karadimitriou, Nikolaos; Lee, Dongwon; Steeb, HolgerEnzymatically induced calcite precipitation (EICP) in porous media can be used as an engineering option to achieve precipitation in the pore space, for example, aiming at a targeted sealing of existing flow paths. This is accomplished through a porosity and consequent permeability alteration. A major source of uncertainty in modeling EICP is in the quantitative description of permeability alteration due to precipitation. This report presents methods for investigating experimentally the time‐resolved effects of growing precipitates on porosity and permeability on the pore scale, in a poly‐di‐methyl‐siloxane microfluidic flow cell. These methods include the design and production of the microfluidic cells, the preparation and usage of the chemical solutions, the injection strategy, and the monitoring of pressure drops for given fluxes for the determination of permeability. EICP imaging methods are explained, including optical microscopy and X‐ray microcomputed tomography (XRCT), and the corresponding image processing and analysis. We present and discuss a new experimental procedure using a microfluidic cell, as well as the general perspectives for further experimental and numerical simulation studies on induced calcite precipitation. The results of this study show the enormous benefits and insights achieved by combining both light microscopy and XRCT with hydraulic measurements in microfluidic chips. This allows for a quantitative analysis of the evolution of precipitates with respect to their size and shape, while monitoring their influence on permeability. We consider this to be an improvement of the existing methods in the literature regarding the interpretation of recorded data (pressure, flux, and visualization) during pore morphology alteration.Item Open Access Benchmark simulations of dense suspensions flow using computational fluid dynamics(2022) Haustein, Martin A.; Eslami Pirharati, Mahmoud; Fataei, Shirin; Ivanov, Dimitri; Jara Heredia, Daniel; Kijanski, Nadine; Lowke, Dirk; Mechtcherine, Viktor; Rostan, Daniel; Schäfer, Thorsten; Schilde, Carsten; Steeb, Holger; Schwarze, RüdigerThe modeling of fresh concrete flow is still very challenging. Nevertheless, it is of highest relevance to simulate these industrially important materials with sufficient accuracy. Often, fresh concrete is assumed to show a Bingham-behavior. In numerical simulations, regularization must be used to prevent singularities. Two different regularization models, namely the 1) Bi-viscous, and 2) Bingham-Papanastasiou are investigated. Those models can be applied to complex flows with common simulation methods, such as the Finite Volume Method (FVM), Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Within the scope of this investigation, two common software packages from the field of FVM, namely Ansys Fluent and OpenFOAM, COMSOL Multiphysics (COMSOL) from FEM side, and HOOMD-blue.sph from the field of SPH are used to model a reference experiment and to evaluate the modeling quality. According to the results, a good agreement of data with respect to the velocity profiles for all software packages is achieved, but on the other side there are remarkable difficulties in the viscosity calculation especially in the shear- to plug-flow transition zone. Also, a minor influence of the regularization model on the velocity profile is observed.Item Open Access High‐speed fatigue testing of high‐performance concretes and parallel frequency sweep characterization(2023) Madadi, Hamid; Steeb, HolgerCycling loading of brittle materials like ultra‐high‐performance concrete (UHPC), which is often used in marine and civil structures, results in unexpected failures. When a material is subjected to cyclic loading, its mechanical properties change due to the evolution of (micro‐)fractures often denoted as damage. To better understand the effective material's properties under such kind of fatigue load and to relate the material's properties to the specific time‐dependent loading characteristics, the mechanical response of the material shall be characterized at characteristic harmonic excitations. Therefore, cyclic loading experiments are conducted to determine how the evolution of microfractures, that is, fatigue, affects the material's effective mechanical properties and after how many cycles microfractures further evolve towards meso‐ and macrofractures leading finally to a critical number of cycles to material's failure. The problem with such cyclic fatigue tests is that they are potentially “expensive” to conduct as the number of loading cycles at failure can be extremely high. Moreover, it is not possible to observe and characterize further the evolution of (micro‐)fractures within the different damage phases of the cycling experiment. Further, it is challenging to characterize the material's small‐strain stiffness evolution. In this investigation, a combination of a (high‐amplitude) high‐frequency excitation and a high‐speed fatigue testing approach is used for the high cycle fatigue experiment along with a characterization approach of the material properties using a (low‐amplitude) dynamic mechanical analysis (DMA). The test setup applies harmonic excitations for high and low amplitudes using a high‐voltage piezoelectric actuators. Furthermore, the failure modes of the material will be examined. The excitation frequency 𝑓 for the fatigue test is significantly higher than in classical low- and high-cyclic fatigue approaches, that is, 10 < 𝑓 < 200 Hz, allowing to reduce the overall time of the experimental investigation time to failure. Further, the frequency-dependent number of cycles to failure is studied. Similar to standard DMA, effective complex mechanical properties of the material in tangential space are obtained in frequencies between 0.01 and 1000 Hz; while the observed mechanical properties of these materials change with increasing frequency. In the case of materials' behavior, by increasing the frequency, Young's modulus increases and Poisson's ratio decreases. Experimental fatigue results will be presented for UHPC samples. Harmonic experimental data include (direct) strain measurements in axial and circumferential directions as well as forces in axial directions. In addition, the resulting complex Young's modulus and evolving damage‐like “history” of UHPC will be shown.