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Porównawcza analiza metod wyznaczania współczynników dyfuzji na przykładzie sorpcji CO₂ i CH₄ w węglach kamiennych

Marecka A.

Przemysł Chemiczny

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2014

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T. 93, nr 11

1953-1959

PL

Przedstawiono wyniki badań kinetyki procesu sorpcji i dyfuzji CO₂ i CH₄ na dwóch węglach kamiennych o różnym stopniu uwęglenia. W analizie danych empirycznych wykorzystano procedurę wielostronnej analizy porównawczej metod estymacji parametru kinetycznego z wykorzystaniem dwóch modeli (II prawo Ficka, trzy formy matematyczne oraz model kinetyczny F2). W rozważaniach przyjęto zaproponowaną wcześniej koncepcję estymacji parametrów kinetycznych na przykładzie obliczeń modelowych dla sorpcji gazów na antracycie w szerokich granicach uziarnienia (od poniżej 0,03 mm do 1,5 mm). Przedyskutowano również zależności między estymowanymi parametrami, w ujęciu równania Arrheniusa, na podstawie analizy danych kinetycznych otrzymanych w kilku temperaturach (ciśnienia poniżej 0,1 MPa, warunki izotermiczno-izobaryczne). Zastosowane podejście, które stanowi pewną modyfikację klasycznego modelu dyfuzji wg II prawa Ficka oraz przeprowadzone analizy wartości estymowanych parametrów znacznie rozszerzają możliwości analizowania eksperymentalnych krzywych kinetycznych i umożliwiają porównanie natury złożonych procesów sorpcyjnych w kompleksowej strukturze węgli kamiennych o zdecydowanie odmiennych właściwościach fizykochemicznych i teksturalnych.

EN

Two bituminous coals (C contents 87.58 and 92.30% by mass, pore vols. 0.0549 and 0.0560 cm³/g, resp.) were used as sorbents (grain size 0.49–0.75 mm) for CO₂ and CH₄ sorption at 289–313 K and below 0.1 MPa to det. The kinetic consts. in the F2 kinetic model and the diffusion parameters in the Fick equation (after its transformation). Mechanism and kinetics of the sorption were discussed in aspects to CH₄ recovery from coal beds and CO₂ storage in the beds. The applicability of the 2nd Fick law for the description of the sorption on coals was confirmed.

2

Modelling of mass transport in watercourses at unsteady states

Bielski A.

Environment Protection Engineering

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2012

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Vol. 38, nr 3

159--173

EN

In terms of quality particularly difficult to describe are processes of mass exchange between different phases (e.g., atmospheric air-water, water-river sediment, water-algae, etc.). Whitman's model is most often used to describe the mass transport processes through the phase boundary. Theoretical analysis of the mass transfer process through the phase boundary showed that in unsteady states, the calculation results obtained from Whitman's model differ from the results obtained using the accurate diffusion model. These differences are due to the fact that concentration profiles in the direction of diffusion process change in time. Assumptions for Whitman's model do not include changes in the concentration distribution over time. Therefore, the correction factor was introduced to Whitman's model. The correction factor is defined as a parameter that multiplies a concentration derivative over time in the mass transport model. The correction factor can be used to estimate the effective diffusion coefficient of the substance that permeates from the aqueous phase to the sediment. The correction factor improves the degree of fit of the mass transport model to the measurement data. It can be used to estimate the effective turbulent diffusion coefficient from water phase to the sediment phase.

3

Transport of Phenanthroline Complexes of Manganese(II) Ions through Nafion Layer on Glassy Carbon Electrode

Nowak L., Andrijewski G., Tomczyk D., Błaszczyk T.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 12

2195-2203

EN

Apparent diffusion coefficients of [Mn(phen)2(H2O)2]2+ and [Mn(phen)3]2+ in Nafion layer on glassy carbon electrodes were calculated and discussed. Charge transport mechanism was qualified on the basis of voltammetric and coulometric measurements and confirmed by use of the impedance spectroscopy. Electrocatalytic activity against several reductants (glycol aldehyde, glycol acid and ascorbic acid) was examined.

4

Non-equilibrium statistical mechanics formulation of thermal transport properties for binary and ternary gas mixtures

Avsec J., Naterer G., Marcic M.

Archives of Thermodynamics

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2008

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Vol. 29, no. 2

21-46

EN

The paper develops a new statistical formulation to calculate the thermal diffusivity, binary diffusion coefficient, thermal diffusion factor, viscosity and thermal conductivity of gas mixtures with non-equilibrium statistical mechanics. For the analytical calculation of transport properties, the models of Kihara and Chapman-Cowling (up to the third order) have been used. Thermal transport properties for mixtures involving carbon monoxide, helium, argon, xenon and krypton have been computed with the new formulation in this paper. New mixing rules for the calculation of transport properties for mixtures are developed. Close agreement is obtained between the analytical results (based on statistical mechanics) and experimental data. The results exhibit comparable or better accuracy than previous methods, while providing new insight regarding the detailed statistical mechanisms of intermolecular interactions, as they contribute to the transport property variations with temperature.

5

Investigation of low temperature diffusion of carbon in martensite by Mössbauer spectroscopy and X-ray diffraction

Jabłońska A., Dąbrowski L., Suwalski J., Neov S.

Nukleonika

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2006

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Vol. 51, nr 2

101-104

EN

Martensite containing 0.87 wt.% carbon was studied by Mössbauer spectroscopy at temperatures, T = 10, 15, 25, 40 and 78 K and by X-ray diffraction at T = 78 K in the course of 35 days. Samples in the form of 30 mm thick foil of pure carbon martensite with enhanced tetragonality were synthesized applying non-standard technology. The measured by X-rays (c/a - 1) ratio varies within the limits 0.044-0.055 by pulsations with a period of few hours. According to Kurdimov’s model any changes in tetragonality of martensite are fully related to the passage of carbon atoms from Oc to Oa and Ob octahedral sites or vice versa. Pulsations of the central and satellite sextets were observed by Mössbauer spectroscopy. In accordance with the conventional interpretation of satellites, these pulsations result from different spatial distribution of carbon around the Fe atoms in the diffusion process. The data of (c/a - 1) pulsations were used to determine the diffusion coefficient below 78 K. The measured diffusion coefficient of carbon in a-iron below 78 K contradicts the classical approach to the observed temperature dependence. As the temperature is lowered below 78 K, the diffusion constant approaches the nearly temperature-independent value. The low temperature branch is apparently characteristic of a quantum mechanical process dominated by tunnelling in the ground state.