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

Oblique shock reflection from an axis of symmetry: shock dynamics and relation to the Guderley singularity

Oblique shock reflection from an axis of symmetry is studied using Whitham's theory of geometrical shock dynamics, and the results are compared with previous numerical simulations of the phenomenon by Hornung (2000). The shock shapes (for strong and weak shocks), and the location of the shock-shock (for strong shocks), are in good agreement with the numerical results, though the detail of the shock reflection structure is, of course, not resolved by shock dynamics. A guess at a mathematical form of the shock shape based on an analogy with the Guderley singularity in cylindrical shock implosion, in the form of a generalized hyperbola, fits the shock shape very well. The smooth variation of the exponent in this equation with initial shock angle from the Guderley value at zero to 0.5 at 90° supports the analogy. Finally, steady-flow shock reflection from a symmetry axis is related to the self-similar flow

Gendered Educational Participation and Attainment in South Africa

Across much of the developing world, and in sub-Saharan Africa in particular, there are large gender disparities in educational participation and achievement. Educating girls has powerful externalities, which, if scaled, can act as a catalyst for socioeconomic development. It is therefore important to understand the reasons for the widespread gender disparity in education. South Africa appears to be unusual in that it has successfully achieved gender parity in educational enrolment. This paper finds that South Africa's gender parity in enrolment is not as unique as it might seem. Whilst it is distinctive geographically, in comparison with most African countries, it is not so distinctive economically. Other middle-income countries in Africa and elsewhere tend also to have achieved gender parity in education. Over time, also, South Africa seems to be a typical middle income country in terms of its gender disparity in education. The paper also demonstrates that girls' success in terms of educational enrolment and attainment is matched by girls' superior test scores and record in grade progression

Gendered Educational Participation and Attainment in South Africa

Across much of the developing world, and in sub-Saharan Africa in particular, there are large gender disparities in educational participation and achievement. Educating girls has powerful externalities, which, if scaled, can act as a catalyst for socioeconomic development. It is therefore important to understand the reasons for the widespread gender disparity in education. South Africa appears to be unusual in that it has successfully achieved gender parity in educational enrolment. This paper finds that South Africa's gender parity in enrolment is not as unique as it might seem. Whilst it is distinctive geographically, in comparison with most African countries, it is not so distinctive economically. Other middle-income countries in Africa and elsewhere tend also to have achieved gender parity in education. Over time, also, South Africa seems to be a typical middle income country in terms of its gender disparity in education. The paper also demonstrates that girls' success in terms of educational enrolment and attainment is matched by girls' superior test scores and record in grade progression

Paul Academic Excellence Luncheon

Paul Academic Excellence Luncheon was the current project I was handling at the time that seemed to fit well with the process I was about to learn. The project was a new one, at the time in 2013, and we had decided to appreciate the students in our school who had worked hard to receive grades of 3.8 GPA or higher. We began with an elegant invitation to an elegant luncheon where an alumni would speak, certificates were handed out and pictures were taken. The project was successful and the students appreciative. Having the step by step tasks written out has become a valuable asset to our office in determining future events and their value. The luncheon, since 2013, has changed with the help from our stored data into a yearly event of appreciations now saving us money and hours for the future

Filter Cleaning Using Gas Injection

A filter cleaning process using gas injection is considered. An estimate for the minimum mass flow rate out of the gas injector and the corresponding injector/filter geometry is found. The estimates are based on a similarity solution for a free turbulent jet. The minimum mass flow rate and geometry is worked out for a specific example