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Transport of Gaseous Mixtures in a Porous Membrane Support Modelled Using a Random Three-Dimensional Pore Network
Čapek, P. ; Veselý, M. ; Hejtmánek, Vladimír
In this paper, we developed a pore network model of multi-component mass transport in porous solids. Constitutive equations applied on the pore-scale level were based on the Maxwell-Stefan formulation. Fitting effective transport parameters like tortuosity was completely avoided. Essential information about pore sizes was extracted from the pore network model. It was shown that conditions for unusual phenomena, particularly up-hill flow, can be found quite often in practice. Pore network models also appear to be a very convenient tool for estimation of optimal conditions of diffusion experiments.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22014050212450 - PDF
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Process-Based Model of Mixed-Matrix Membrane
Čapek, P. ; Hejtmánek, Vladimír ; Veselý, M. ; Sysel, P. ; Kočiřík, Milan ; Brabec, Libor ; Zikánová, Arlette ; Bernauer, B. ; Fíla, V.
The focus of this contribution was on the formulation and verification of a process-based model of the mixed-matrix membrane that consisted of the polyimide matrix synthesized from the monomers 4,4’-(hexafluoroisopropylidene)diphtalic anhydride and 4,4’-oxydianiline, and silicalite-1. When a solution of a polyimide precursor in N,N-dimethylformamide was ready, silicalite-1 particles were dispersed in the solution and the dispersion was subsequently cast on a Teflon support plate. An initial mass ratio of silicalite-1 and polyimide was about 1:1. After solvent removal, the films were heated in subsequent steps up to 230°C for two hour. From a process-based model point of view, a key operation of the entire synthesis was slow sedimentation of silicalite particles in the viscous solution. Preliminary observation of 2D cuts through the solid membrane in a scanning electron microscope revealed that there were a lot of contacts among the silicalite particles. Therefore, a sequential (ballistic) deposition algorithm, well representing sedimentation in a low-energy environment, was used to create an off-lattice model of spatial distribution of the silicalite particles in the polyimide matrix.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22012102413461 - PDF
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Microbial biomass phosphorus measured by extraction-fumigation method
ČAPEK, Petr
The aim of this study was to assess posible sources of unacuracy in measurement of soil microbial phosphorus by extraction-fumigation method. The biggest one is the correction for sorption in two forest soils of watershed Plešné lake and Čertovo lake and one waterlodged soil. We also tried to assess the correction factor (Kp) for these soils, but we were unsuccesful. We would like to assess extractability of phosphorus sorbed during fumigation and assess Kp factor in future. Therefore we set up an appropriate methodology.
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\kur{In-situ} available phosphorus in forest soils of Bohemian forest lakes watersheds
ČAPEK, Petr
The aim of the study was to test ion exchange resin (IER) bag method for measurement of forest soil phosphorus availability. P-PO4 sorption and elution efficiencies of ion exchange resin AsenXnp (Purolite) were tested. The results showed nearly 100% efficiency of P-PO4 sorption. Average elution efficiency after repeated elution on a glass column was 87 % (each elution step 50 ml 2 % NaOH, 300 ml in total). The amount of available phosphorus was determined in-situ using IER bag method in the litter and organic soil layers of Plešné and Čertovo lakes watersheds. Amount of available phosphorus was 3.6 times greater in soils of Plešné watershed compared to Čertovo watershed.
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Reconstructed 3D Microstructure and Effective Diffusivity of a Zeolite-Polyimide Mixed Matrix Membrane
Čapek, P. ; Hejtmánek, Vladimír ; Fryčová, M. ; Sysel, P. ; Kočiřík, Milan ; Brabec, Libor ; Zikánová, Arlette ; Bernauer, B. ; Fíla, V.
In our work we focused on a two-phase system consisting of the polyimide matrix synthesized from the monomers 4,4’-(hexafluoroisopropylidene)diphtalic anhydride (6FDA) and 4,4’-oxydianiline (ODA), and silicalite-1 [3, 4]. Its microstructure on the scale capturing the morphology of silicalite particles was reproduced by means of stochastic reconstruction. Then, effective diffusivity of an arbitrary fluid in the reconstructed composite material was determined by exploiting random walk simulation. Resulting values were compared with the corresponding values obtained using two traditional correlations for conductivity of composite materials. Image processing and analysis as the first step of stochastic reconstruction was a bit inexact in terms of an estimation of the volume fractions of both phases.
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Analysis of Gas Transport through Macroporous Media.
Čapek, P. ; Hejtmánek, Vladimír
The aim of this study was to evaluate diffusional and forced flow in the cylindrical capillary under defined boundary conditions and to determine the effective diffusivities of gases (hydrogen, nitrogen, helium, and argon) in selected macroporous media. The knowledge of these diffusional and forced flow densities helps us to formulate many demands on the experimental apparatus and to estimate the error of the effective diffusivity. The relation between molar flux and the molar concentration gradient was described by the model of the mean transport pore. The experimental values of the effective diffusivities have agreed with the ones calculated for porous media replicas very well.
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