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The Proper Use of Mass Diffusion Equations in Drying Modeling: Introducing the Drying Intensity Number

Abstract : This article intends to clearly define the possibilities and limitations offered by a simple diffusion approach of drying. Actually, many works use a simple diffusion equation to model mass transfer during drying, probably because a simple analytical solution of this equation does exist in the case of simple boundary conditions. However, one has to be aware of the limitations of this approach. Using a comprehensive formulation and a relevant computational solution, the most frequent assumptions of the diffusion approach were rigorously tested. It is concluded that analytical solutions must be discarded for several reasons: analytical solutions, either using Dirichlet or third kind boundary conditions, are often misleading and should be avoided; in the drying process, the coupling between heat and mass transfer is mandatory; nonlinearity (variation of diffusivity with moisture content) can hardly be avoided for mass transfer. In order to reach a verdict, a dimensionless number, the Drying Intensity Number (NDI), is introduced. It allows the level of coupling between heat and mass transfer to be easily assessed. Thanks to this number, a guide is proposed for choosing the right level of modeling, depending on the drying configuration.
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Submitted on : Thursday, December 3, 2015 - 3:03:34 PM
Last modification on : Thursday, August 20, 2020 - 10:52:52 AM

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Patrick Perre. The Proper Use of Mass Diffusion Equations in Drying Modeling: Introducing the Drying Intensity Number. Drying Technology, Taylor & Francis, 2015, Special Issue: Selected Papers from the 19th International Drying Symposium (IDS 2014), Part 2, 33 (15-16), pp.1949-1962. ⟨10.1080/07373937.2015.1076836⟩. ⟨hal-01237608⟩

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