摘要:

This research deals with the physical mechanisms that occur during drying of a paper coating. A study at the local scale of the drying of a paper coating coupled with natural binder (starch) migrations is carried out. In this aim, drying experiments have been realized and lead to the determination of drying kinetics, time evolution of moisture content profiles, and starch concentration distribution at the end of drying. The results obtained allow the modelling to be validated. This model, which is based on diffusive liquid transport, takes into account the shrinkage of the coating and the migration of the different solid components during drying. It leads us to suggest that starch migration occurs until the coating is totally consolidated.

ISSN:0737-3937    

DOI:10.1080/07373939708917352

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A study of drying of textile fabrics on a drum heated by natural gas burner is presented. In the first stage of study, the distribution of the heat flux over the outer surface of the drum is calculated by an analytical method. In the second stage, this heat flux is entered in a numerical code able to simulate the heat and mass transfers in porous media. The simulation results validate the analytical model assumptions. Special attention is paid to the contact resistance between the drum and the fabric.

ISSN:0737-3937    

DOI:10.1080/07373939708917353

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The kinetics of combined convective and micro-wave drying presents universally more than the two habitual drying phases. Superimposed to a general heating of the product, a brutal and short acceleration of the drying rate raises all flux densities at a very important level. This is particularly evident with the class of product we used in this study : non porous polymeric gels.

ISSN:0737-3937    

DOI:10.1080/07373939708917354

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Vacuum drying and especially discontinuous vacuum drying is a very attractive process for such a wood as oak, because of a reduced drying time and a high quality of the final product. In this paper, a model describing heat, mass and momentum transfer in a capillary porous and hygroscopic medium under vacuum drying with no external heating agent (the material is pre-heated during a convective phase), is presented. The choice of the following three independent unknowns, moisture content, enthalpy and dry air density, leads to a fully well described problem where the effect of gaseous pressure inside the material is taken into account. A new formulation of the boundary conditions and its numerical resolution are validated by experimental results.

ISSN:0737-3937    

DOI:10.1080/07373939708917355

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper presents a synthesis of our scientific activity in the area of heat and moisture transfers in capillary-porous bodies. The materials which have been under investigation are essentially in the field of Civil Engineering but our ways of experimentation may be generalized.

ISSN:0737-3937    

DOI:10.1080/07373939708917356

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A model taking into account the simultaneous influence of mechanical and hygrometric actions (Mrani and al., 1995a, 1995b) was applied to study of the dehydration of a cylinder of highly deformable biphase gel (agar gel) (Mrani and al., 1995b). Numerical solution of the water transport equation and the mechanical equilibrium equation provided access to the water content and stresses and strains in the cylinder. The numerical results were validated for water content and overall deformation of gel cylinders. The model clearly shows the inversion of the curve of the faces of the cylinder observed experimentally. Three deformation phases were observed. In the first phase, when the concaveness of the faces of the cylinder was turned inwards, tractive stress appeared at the surface of the sample. More uniform distribution of the water content became established in a second phase and the cylinder recovered its initial shape corresponding to the relaxation of the stress state. In the third phase, the concaveness of the faces of the cylinder was turned outwards, the surface became rigid with compression at the surface and traction in the centre.

ISSN:0737-3937    

DOI:10.1080/07373939708917357

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper presents the main activities of the Gas Fluidization and Drying Team of the Chemical Engineering Laboratory at Toulouse. The emphasis has been put on the modeling of a fluidized bed dryer and its derivates such as a flotation fluidized bed, by the analysis of heat and mass transfer together with the physico-chemical transformations of the product during drying. Several studies have been performed on different solids (cereal and chemical products) to illustrate the effect of the operating conditions on dehydration and degradation kinetics The knowledge of heat and mass transfer coefficients in flotation fluidized bed allows to determine intrinsec drying and degradation kinetics. These kinetics can be used in any conductive or convective drier model.

ISSN:0737-3937    

DOI:10.1080/07373939708917358

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper has been written for a special issue devoted to the works done in France in the field of drying. Therefore, it aims, through numerous examples, to show the spirit which initiates and guides the research work of the Forest Products Unit at ENGREF : how more and more microscopic information can be included in the study of the drying process ?

ISSN:0737-3937    

DOI:10.1080/07373939708917359

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This work focused on high-temperature convective drying (superheated steam drying). The process has been investigated both experimentally and numerically. The experimental analysis was carried out in an aerodynamic return-flow wind-tunnel, with very small cylinders of cellular concrete. For the local analysis, the samples were fitted with thermocouples and pressure sensors. The mean moisture content of the cylinders was measured by simple weighing while the temperature and pressure readings were being taken. Global and. local analysis of heat and mass transfer in small cylinders in superheated steam were carried out. The systematical study for several sizes and aerothermal conditions show a similar behavior for moisture content, pressure and temperature values. A numerical model for high temperature drying, using the finite elements method, in a 2-D configuration, was implemented and validated.

ISSN:0737-3937    

DOI:10.1080/07373939708917360

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A method for multicriteria optimization is illustrated by the example of apples processed by Dewatering and Impregnation Soaking (DIS) in concentrated aqueous sucrose solutions, and then air dried. The influence of the product history (modifications linked to DIS treatment) on its behaviour during drying process is assessed according to an experimental design. Five operating variables are taken into account: temperature, solution concentration and soaking time for DIS pre-step, and temperature and relative humidity for air drying. Results show a limiting effect of internal water transport by the sucrose impregnated superficial layer. This effect can be reduced by drying at high temperature (80°C). On the other hand, the relative humidity of air has little influence on the behaviour of soaked materials. Multicriteria optimization takes into account six criterias and shows that stable and optimal quality products can be obtained at interesting energetic costs and for a short processing time duration (50 to 300 min).

ISSN:0737-3937    

DOI:10.1080/07373939708917361

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor