No description available.

A comprehensive microscale model of transport phenomena in paper drying was developed. The model includes five species (free water, sorbed water, air, water vapor, fibers) in three phases: humid air, liquid, solid. AlI relevant transport mechanisms were treated: capillary transport of free water, diffusion of sorbed water, convective-diffusive transport of water vapor. Effects on drying from the hygroscopic nature of paper were included: the reduced vapor pressure and extra evaporation energy for bound water and the changes in porosity and thickness because of sorbed water removal. / Un modèle détaillé des phénomènes de transport à petite échelle a été développé pour le séchage du papier. Le modèle inclut cinq espèces (eau libre, eau sorbée, air, vapeur d'eau et fibres) et trois phases: air humide, liquide et solide. Tous les mécanismes de transport pertinents du séchage ont été traités: le transport par capillarité de l'eau libre, la diffusion de l'eau sorbée ainsi que le transport de la vapeur d'eau par convectiondiffusion. Plusieurs effets sur le séchage de la nature hygroscopique du papier ont été inclus: l'énergie supplémentaire nécessaire à l'évaporation de l'eau liée, la réduction de la pression de vapeur de l'eau liée et les changements de porosité et d'épaisseur provenant de l'enlèvement de l'eau sorbée. fr

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No description available.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1960. / Bibliography: leaves 127-129.

Thesis (Ph. D.)--Institute of Paper Science and Technology, Georgia Institute of Technology, 2001. / Includes bibliography.

At Mondi Paper Ltd, Merebank, South of Durban, Paper Machine 2 has recently been transferred onto a Distributed Control System (DCS). This was seen as a good opportunity to enhance the control of the pulp feed to the machine. A prime concern in operating a paper machine is to ensure consistent set-point paper properties in the Cross-Direction (CD: ie. across the paper width) and in the Machine-Direction (MD: ie. along the paper length). Sophisticated adjustments are available to ensure an even feed of the stock (consistencies around 2% m/m wood fibres in water) from the head-box across the receiving width of the paper machine. The properties of prime interest as the pulp is pumped through the head-box distributor onto the receiving belt of the machine are the basis weight (fibre mass per unit area) and moisture content (per unit area). However, the distribution system is highly dependent on the properties of the stock as it arrives at the head-box. Variations in upstream chest levels, the supplied pressure, flow-rate and fibre/water ratio, all cause MD and even CD variations. The problems of maintaining steady conditions at the head-box are well known, and are understood to arise from sub-optimal control in the preceding section involving a blend chest and machine chest, amongst other items, where several pulp streams and dilution water are combined. A number of control loops are involved, but appear to require different tuning for different paper grades. Often individual loops are taken off-line. In this study, an understanding of the controller interactions in the stock preparation section has been developed by detailed dynamic modelling, including all of the existing control loops. The model is built up in a modular fashion using a basic element, having one input (which can collect multiple streams originating elsewhere) and four outputs, linked through a vessel of variable volume. Several basic elements are linked together to form the overall system. All of the necessary properties can be defined so that the model allows the simulation of all features of the network: vessels, pipes, junctions, valves, levels and consistencies. A set of first order differential equations is solved which includes total water balance, species mass balances, derivatives of flow controller action, and derivatives of supervisory controller action. Supervisory controllers for consistency or level cascade onto flow controllers. Flow controllers manipulate valves which give a first-order dynamic response of actual flow. Where valves are manipulated directly by the supervisory level, the flow controller is effectively bypassed. This study involves a constraint problem around the blend chest, resulting in a loss of specification at the paper machine. This was solved by the implementation of a static optimiser. Its objective function penalizes deviations from setpoint of five parameters (ratios, consistency and level) using respective weight factors. Both the model and its optimiser were included in a simulator designed with the graphical user interface (GUI) of Matlab. The simulator has then been used to explore control performance over the operating range, by means of a set of scenarios. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2004.

No description available.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1937. / Patents of slice, and headbox ; 1920-June, 1936: p. 73-114. Includes bibliographical references (p. 55).