Drying kinetics; a comparison of diffusion coefficients from moisture concentration profiles and drying curves
| Autor: | Leo L Pel, P.J.A.M. Kerkhof, W.J. Coumans, A. A. J. Ketelaars |
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| Přispěvatelé: | Transport in Permeable Media, Chemical Reactor Engineering |
| Jazyk: | angličtina |
| Rok vydání: | 1995 |
| Předmět: |
Work (thermodynamics)
Diffusion equation Moisture Chemistry Applied Mathematics General Chemical Engineering Thermodynamics ComputingMilieux_LEGALASPECTSOFCOMPUTING General Chemistry Industrial and Manufacturing Engineering Physics::Geophysics Mass transfer Effective diffusion coefficient Grain boundary diffusion coefficient Diffusion (business) Water content Physics::Atmospheric and Oceanic Physics |
| Zdroj: | Chemical Engineering Science, 50(7), 1187-1191. Elsevier |
| ISSN: | 0009-2509 |
| Popis: | The mathematical formulation of mass transfer in drying processes is often based on the diffusion equation. In principle the diffusion coefficient as a function of moisture content has to be determined experimentally. The most direct approach is to derive the diffusion coefficient from experi- mental moisture concentration profiles in the material during drying. In this work, the diffusion coefficient determined in this way is called the actual diffusion coefficient. Very often, however, an indirect method is used based on drying curves (average moisture content of a sample vs time). Since the diffusion coefficient is determined indirectly from the macroscopic behaviour of the sample, this coefficient will be called the apparent diffusion coefficient. A comparison of diffusion coefficients as a function of moisture content using both methods shows that for porous materials such as clays, the apparent diffusion coefficient depends on experimental conditions. This can be explained by the fact that the apparent diffusion coefficient is in agreement with the actual diffusion coefficient over a limited range of moisture content only. For materials such as clays, drying curves are not suited to derive diffusion coefficients as a function of moisture content in a satisfactory and consistent way. |
| Databáze: | OpenAIRE |
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