Transport phenomena over partially active surfaces
| Autor: | Achim Stammer, W Büssing, Ernst‐Ulrich Schlünder |
|---|---|
| Rok vydání: | 1991 |
| Předmět: |
Differential equation
Chemistry Process Chemistry and Technology General Chemical Engineering Diffusion Finite difference Energy Engineering and Power Technology Thermodynamics General Chemistry Active surface Industrial and Manufacturing Engineering Boundary layer Mass transfer Boundary value problem Transport phenomena |
| Zdroj: | Chemical Engineering and Processing: Process Intensification. 30:125-132 |
| ISSN: | 0255-2701 |
| DOI: | 10.1016/0255-2701(91)85001-5 |
| Popis: | Transport phenomena over partially active surfaces have been examined theoretically and experimentally. Boundary conditions of the first and third kind have been considered. The theoretical results were achieved by solving the Laplace differential equations with mixed boundary conditions at the surface. The solution methods of conformal mapping, Fourier series and finite differences for boundary conditions of the first kind are discussed and compared with the simple model of Schlunder. There is good agreement if the fraction of active surface is larger than 2%. For boundary conditions of the third kind (e.g. first-order reaction) the model had to be extended and is thereafter in qualitative agreement with the differential equation solution. Our calculations show only a weak dependence of the mass transfer rate on the fraction of active surface. The decrease with active surface fraction is slower if the boundary layer is thick, the active patches are small and the reaction is slow compared with diffusion. As an example of a boundary condition of the first kind, evaporation through a perforated foil was examined. The catalytic combustion of hydrogen at partially active surfaces was studied as an example of a boundary condition of the third kind. The experimental results confirm the expected dependence of overall mass transfer on the active surface fraction, although the experimental data show reasonable scattering in the case of the catalytic reaction. These deviations are due to problems in achieving a uniform and constant catalytic activity during the measurements. |
| Databáze: | OpenAIRE |
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