The Dynamics of a Roll Press Nip

The problem presented concerned the dynamics of a roll press nip, a crucial component in a paper-making machine. Modern commercial paper-making machines are huge items of equipment. They may be as long as a football field and cost many millions of dollars each. Integrity of the process is extremely important; the paper in such a machine travels so fast (up to 20 km/sec) that a break is viewed as a major calamity and may take many man-hours and dollars to recover from. The size and speed of the machines means that it is not easy to make measurements as the paper passes through. The hostility of the environment therefore dictates that a thorough theoretical understanding of the important parts of the process is crucial if the processes involved are to be optimized. In this study we do not seek to answer anyone specific question, but rather wish to propose a general framework for modeling the flow and deformation under a roll press nip. Because of the difficulty of making measurements in the nip region and the need to closely control the process, the distributions of pressure, velocity and felt porosity within the nip have traditionally been subjects of great debate. Previous treatments have included lubrication theory models and "Bernoulli" based models. Although some progress may be made using thin layer theory, we shall show the required modeling does not take the form of standard lubrication theory. As far as models based on Bernoulli's equation are concerned, we simply note that the discussion below shows that the drag force exerted by the felt on the liquid is a key physical component of the flow process. Clearly, a full three-phase flow treatment is required. In this study we will thus address the following questions: (i) Is it possible to propose a general theoretical treatment of the roll press nip? (ii) What determines the physics of the water movement within the paper and felt in the roll press nip and how is this connected to the details of the air movement and the deformation of the felt? (iii) When a general model has been proposed, is it possible exploit the geometry within the nip to generate some simple exact solutions? (iv) What are the key non-dimensional parameters in the problem and how large are they likely to be for realistic paper-making machines? A further matter of interest concerns the influence that the size, shape and separation of the rollers have on the whole process. We approach the modeling from a rather general point of view, beginning by including all effects that might be important and then making clearly defined assumptions to simplify the equations. In this way it is possible to make changes to the model if circumstances change

The application of cellular automata to weather radar

A possible cellular automaton approach to weather (and in particular rainfall) modelling is considered. After posing a paradigm problem in a manner reminiscent of a numerical PDE solver and showing that the general approach appears to be valid, we consider some more detailed modelling and comment on how this could be used to construct a genuine finite-state cellular automaton

Vacuum moulding of a superplastic

The objective of this research is to develop a model for simulating the super-plastic forming process and for predicting the thickness distribution as well the minimum radius of curvature when the material has to fill a sharp corner. Other questions of interest are the deflection of the sheet as a function of pressure for a given mould opening, and the deflection as a function of mould diameter for a given pressure. Modeling based on shell theory is carried out for cylindrical, spherical and arbitrary-shape shells of uniform as well as non-uniform thick- nesses

Furnace problem

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Modelling surface heat exchanges from a concrete block to the environment

The presented problem was to determine an appropriate heat transfer boundary condition at the surface of a concrete slab exposed to the environment. The condition obtained involves solar radiation and convective heat transfer, other terms were shown to be small compared to these. It is shown that this boundary condition leads to a temperature variation that has qualitative agreement with experiments carried out by the Cement and Concrete Institute