National Repository of Grey Literature 22 records found  previous11 - 20next  jump to record: Search took 0.00 seconds. 
Vícesložkový transport hmoty v nosiči membrán modelovaný pomocí náhodné třírozměrné sítě pórů
Čapek, P. ; Hejtmánek, Vladimír
The main objective of this work is to demonstrate unusual phenomena that attend transport of multicomponent mixtures of ideal gases in the porous membrane support represented by the pore network model. For this purpose, we simulated isobaric counter- current diffusion of binary and ternary mixtures. We also simulated viscous slip flow of multicomponent mixtures in order to show the significance of small pressure gradients on overall mass transport.
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.
Zpracování snímků výbrusů za účelem 3d rekonstrukce pórovitých materiálů
Hejtmánek, Vladimír ; Čapek, P. ; Brabec, Libor ; Zikánová, Arlette ; Kočiřík, Milan
The technique of electron microscopy in SEM/BSE work modes was compared for the purpose of porosity estimation of some porous materials such as potential membrane supports on the basis of a-alumina. To prepare casts, an individual samples were impregnated by epoxide resin AralditO under high vacuum. Every cast was cut, grinded and polished to achieve its smooth face for observation by means of electron microscopy.
Obrazová analýza řezů pórovitého materiálu
Hejtmánek, Vladimír ; Čapek, P.
Two methods of image analysis of cross-sections through two-phase porous media are compared. Linear filtering uses the recursive (IIR) Gaussian filter with the same vertical and horizontal blur radii. The images are also treated by removing small clusters of pixels in the void and solid phases. After linear filtering and before removing small clusters, the grey-level threshold is determined in order to partition all grey pixels into pore and solid pixels. Linear filtering reduces the specific surface very efficiently creating ``smooth'' pore walls and leaves small clusters of pixels in the images. Removing preserves ``rough'' pore walls and removes simultaneously small clusters from both the phases.

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