The interaction of rarefied gases with functionalized surfaces is of great importance in technical applications such as gas separation membranes and catalysis. To investigate the influence of ...functionalization and rarefaction on gas flow rate in a defined geometry, pressure-driven gas flow experiments with helium and carbon dioxide through plain and alkyl-functionalized microchannels are performed. The experiments cover Knudsen numbers from 0.01 to 200 and therefore the slip flow regime up to free molecular flow. To minimize the experimental uncertainty which is prevalent in micro flow experiments, a methodology is developed to make optimal use of the measurement data. The results are compared to an analysis-based hydraulic closure model (ACM) predicting rarefied gas flow in straight channels and to numerical solutions of the linearized S-model and BGK kinetic equations. The experimental data shows that if there is a difference between plain and functionalized channels, it is likely obscured by experimental uncertainty. This stands in contrast to previous measurements in smaller geometries and demonstrates that the surface-to-volume ratio of 0.4
m
seems to be too small for the functionalization to have a strong influence and highlights the importance of geometric scale for surface effects. These results also shed light on the molecular reflection characteristics described by the TMAC.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Strong hierarchical porous zeolite structures are prepared by a sol–gel method using freeze gelation. Instead of conventional binders in powder form, such as bentonite or kaolin, it has been proven ...that using a freeze gelation method based on a colloidal silica sol is a more straightforward and easier-to-use-approach in fabricating highly mechanically stable zeolite monoliths. The resulting zeolite slurries possess superior rheological properties (not being pseudoplastic) and show low viscosities. This low viscosity of the slurry enables an increase in the solid content without compromising the extraordinary good flow behavior for casting applications. Additionally, in comparison to conventional powdery binders, zeolite samples prepared by using a colloidal silica sol exhibit a significantly higher mechanical strength. This mechanical strength can be further improved by either increasing the zeolite content or increasing the silica to zeolite ratio. Increasing the zeolite content leads to an increased volumetric adsorption capacity for CO2 as the test gas, resulting from the increased amount of zeolite particles per unit volume. In addition, a higher solid content of the zeolite monoliths leads to higher compression strengths, while showing the same elastic deformation and brittle failure characteristics. In turn, increasing the silica to zeolite ratio does not affect the volumetric adsorption capacity for CO2. Nevertheless, higher silica contents lead to a significant increase in the elastic deformation and absorbed work until failure. Therefore, the proposed processing route based on freeze gelation presents an easy and unique tool to tune the mechanical and gas adsorptive properties of hierarchically structured zeolite monoliths, according to the application requirements.
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In this work, we study the fatigue behavior of a C/SiC composite produced by several cycles of polymer infiltration and pyrolysis (PIP). Fatigue tests were performed with maximum stresses ...corresponding to 60–90% of the tensile strength of the composite. During the fatigue tests, acoustic emission (AE) monitoring was performed and the measured AE energy was utilized to quantify the damage and distinguish possible damage mechanisms. Most of the fatigue damage in the form of matrix cracking, interface damage and fiber breakage occurs in the first cycle. As loading cycles proceeded, damage in form of matrix crack re-opening and interfacial friction constantly accumulates. Nevertheless, all samples survived the run-out of 1,000,000 cycles. After the fatigue tests, an increase of the tensile strength is observed. This phenomenon is associated with the relief of process-induced internal thermal stresses and the weakening of the fiber-matrix interface. In general, the studied material shows very high relative fatigue limit of 90% of its tensile strength.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Multiple emulsions (ME) are of interest as carrier of active ingredients that can be released in a controlled way. ME are thermodynamically unstable with a strong tendency to coalesce or flocculate, ...resulting in a complex emulsion generation and stabilization process. Typical encapsulation procedures utilize individual batch operation steps for the ME production. In this work, a multistep membrane encapsulation process is proposed to allow the generation of ME in a continuous shear‐sensitive processing through different membrane stages. The stages combine the premix generation, followed by the internal phase production, and the final ME encapsulation step. For each step, a tailored membrane with different surface properties is used and combined into the continuous process.
Multiple emulsions serve as carrier of active ingredients which can be released in a controlled way. The different steps of a novel continuous shear‐sensitive membrane multistage emulsification device are discussed. Consisting of several membranes with tailored surface properties, the proposed low‐shear process is ideal for the encapsulation of sensitive material, such as bacteria.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Damage analyses of a ceramic matrix composite during fatigue and quasi-static loads were performed by acoustic emission (A.E.) monitoring. The material studied was a 2.5D C/C-SiC composite produced ...by chemical vapor infiltration followed by liquid silicon infiltration. The analysis done during the first 200 cycles of a fatigue test showed that the number of A.E. hits is a good parameter for the quantification of damage. Furthermore, the A.E. hit energy was associated with the type of damage. In this sense, the damage developed during the fatigue loading was related to matrix crack initiation, propagation and re-opening, as well as fiber-matrix friction. Quasi-static tests on post-fatigue samples showed that the previous fatigue loadings increased the material`s damage threshold and hindered the development of new damage. Particular attention was given to the sample after 2,000,000 cycles as this sample showed distinct A.E. signals that could be related to fiber debonding.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Membranes showing monomodal pore size distributions with mean pore diameters of 23, 33, and 60 nm are chemically functionalized using silanes with varying chain length and functional groups like ...amino, alkyl, phenyl, sulfonate, and succinic anhydrides. Their influence on the morphology, pore structure, and gas flow is investigated. For this, single-gas permeation measurements at pressures around 0.1 MPa are performed at temperatures ranging from 273 to 353 K using He, Ne, Ar, N2, CO, CO2, CH4, C2H4, C2H6, and C3H8. Results show pore size and pore volume linearly depending on the length of functional molecules, as expected for monolayer deposition. However, the gas flow through functionalized membranes is disproportionally decreased up to a factor of around 10. Hence, the decreased pore size and pore volume cannot explain the large decrease in flow. Furthermore, there is no specific dependency between the decrease in flow and temperature or gas type other than the relation proposed by Knudsen (√RTM)−1. Considering the large variety of functional molecules used, it is very surprising that no correlations between the type of functional group and the flow have been found. The decrease in flow, however, is strongly dependent on the chain length of the silanes (factor of 10 at ∼2 nm length). This leads to the conclusion that the observed effect is not caused by sorption driven processes. It is proposed that steric interactions between functional groups and gas molecules lead to increased residence times on the surface and longer molecular trajectories, which, in turn, lead to a decrease in flow. In membrane design, any surface modification should, therefore, make use of functionalizing agents with chain length as short as possible.
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Multiphase flows are of major importance in today's industrial processes as many products originate from gas‐liquid reactions. The hydrodynamics within the wake behind the bubbles is essential as ...product selectivity is determined by the residence times in these mixing zones. Magnetic resonance imaging (MRI) offers a wide range of options for the investigation of multiphase flows. Here, non‐invasive MRI flow measurements of buoyancy‐driven N2 Taylor bubbles, spatially fixed inside a countercurrent flow of water, are performed. An experimental setup is presented, enabling the generation of Taylor bubbles inside a horizontal bore MRI scanner. Furthermore, a suitable MRI sequence allowing a time‐dependent analysis of the present flow field is described. The obtained MRI results are qualitatively compared to PIV images acquired in the same setup.
Non‐invasive flow measurements of N2 Taylor bubbles in water were performed by magnetic resonance imaging (MRI) in a specially designed experimental setup. A suitable MRI sequence for time‐dependent flow field analysis is described. The obtained MRI results are qualitatively compared to particle image velocimetry results. Local flux changes are well mapped by both methods and are in good agreement.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Porous ceramic capillary membranes made of yttria-stabilised zirconia (YSZ) are presented, which are conditioned for virus filtration by varying the initial YSZ particle size. Compared to polymeric ...membranes, ceramic membranes offer remarkable advantages for filtration processes as they show excellent chemical, thermal and mechanical stability and can easily be cleaned by backflushing. YSZ powders with different particle sizes (30nm, 40nm and 90nm) are individually and mixed processed by extrusion, dried and finally sintered at 1050°C for 2h. The sintered YSZ capillaries are characterised by microstructural analysis including Hg-porosimetry, BET analysis and 3-point bending tests. By increasing the initial YSZ particle size, increased average membrane pore sizes ranging from 24nm to 146nm are obtained. Mechanically stable membranes are provided showing high open porosities of ∼45% and ∼36% for capillaries composed of single and mixed YSZ powders, respectively. By increasing the membrane pore size, reduced virus retention capacities in combination with increased water permeate fluxes are achieved. Capillaries made of YSZ-40nm ensure both, log reduction values (LRV)≥4 for small model bacteriophages MS2 and PhiX174 and high water permeate fluxes (∼30L/(m2hbar)), being suitable for sustainable virus filtration as requested by the World Health Organisation (WHO) and the United States Environmental Protection Agency (USEPA). Due to long-term virus filtration for two weeks, membrane pore plugging is successfully avoided by iterative backflushing and relatively high membrane fluxes in combination with requested LRV 4 level fulfilling the virus filter criterion are achieved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Mesoporous inorganic structures with mean pore diameters of 26 nm are prepared by extrusion based on a yttria stabilized zirconia nanopowder. The sintered capillary membranes serve as model ...structures to investigate the influence of an alkyl-chain (C16) surface functionalization on the gas diffusion kinetics of argon (Ar), nitrogen (N2) and carbon dioxide (CO2) in mesopores. The density of the C16 alkyl-chains immobilized on the membrane surface has an effect on both, gas flow as well as gas selectivity. For low functional group densities (<4 groups nm−2), the gas flow is reduced without having an effect on the selectivity. In contrast, for high alkyl-chain densities (>4 groups nm−2) the mean distance between the C16-chains is reduced to the order of magnitude of the gas molecules leading to a reduction in gas flow and a significant change of the gas selectivity. The selectivity is found to be influenced depending on the molecular diameter of the gas species, being more evident for CO2 compared to Ar and N2, suggesting a separation mechanism more comparable to molecular sieving than to surface diffusion.
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•Homogeneous mesoporous model structure with mean pore size of 26 nm.•Alkyl-surface functionalization (C16) with varying loading capacities.•C16 alkyl-chain density has an effect on both, gas flow as well as gas selectivity.•The gas selectivity is found to depend on the molecular diameter of the gas species.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Porous inorganic capillary membranes are prepared to serve as model structures for the experimental investigation of the gas transport in functionalized mesopores. The porous structures possess a ...mean pore diameter of 23 nm which is slightly reduced to 20 nm after immobilizing C16-alkyl chains on the surface. Gas permeation measurements are performed at temperatures ranging from 0 to 80 °C using Ar, N2, and CO2. Nonfunctionalized structures feature a gas transport according to Knudsen diffusion with regard to gas flow and selectivity. After C16-functionalization, the gas flow is reduced by a factor of 10, and the ideal selectivities deviate from the Knudsen theory. CO2 adsorption measurements show a decrease in total amount of adsorbed gas and isosteric heat of adsorption. It is hypothesized that the immobilized C16-chains sterically influence the gas transport behavior without a contribution from adsorption effects. The reduced gas flow derives from an additional surface resistance caused by the C16-chains spacially limiting the adsorption and desorption directions for gas molecules propagating through the structure, resulting in longer diffusion paths. In agreement, the gas flow is found to correlate with the molecular diameter of the gas species (CO2 < Ar < N2) increasing the resistance for larger molecules. This affects the ideal selectivities with the relation N 2 Ar < Ar CO 2 < N 2 CO 2 . The influence on selectivity increases with increasing temperature which leads to the conclusion that the temperature induced movement of the C16-chains is responsible for the stronger interaction between gas molecules and surface functional groups.
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