A Dissertation Submitted to the Faculty of engineering University of the Witwatersrand, Johannesburg for the Degree of Master of Science in Engineering Johannesburg 1984 / The rate of mass transfer at gas evolving electrodes has been shown to be a strong function of the so-called bubble break off diameter of the gas bubbles leaving the electrode surface. This dissertation shows how the population balance can be applied to the formation of gas bubbles at gas evolving electrodes. This analysis provides a means of predicting the bubble break off aiameter. Experiments were also performed to measure the bubble break off diameter as well as other parameters, such as the rate of bubble growth, used in the population balance moce-i>. The effect of viscosity, electrolyte flowrate and current on the bubble break off diameter is also investigated. The flowrate and current have little effect on the bubble bi ak off diameters, whi.e the break - - - diameters show a decrease in size with increasing viscosity. The bubble break off diameters predicted by the population balance mode, and those measured were significantly larger than those reported in the literature

Thesis (Ph. D.)--Rijksuniversiteit te Leiden, 1970. / Includes bibliographical references (p. 82-83).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1941. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 45).

No description available.

The Boltzmann equation is the basic equation to describe rarefied gas flows. Some kinetic models with simple expressions for the collision term have been proposed to reduce the mathematical complexity of the Boltzmann equation. All macroscopic continuum equations can be derived from the Boltzmann equation or kinetic models through the Chapman-Enskog method, Grad's moment method, etc. This thesis is divided into three parts. In the first part, existing kinetic models (BGK model, ES-BGK model, v(C) -BGK model, S model, and Liu model), and two newly proposed v(C)-ES-BGK type kinetic models are described and compared, based on properties that need to be satisfied for a kinetic model. In the new models a meaningful expression for the collision frequency is used, while the important properties for a kinetic model are retained at the same time. In the second part of this work, the kinetic models (BGK, ES-BGK, v(C) -BGK, and two new kinetic models) are tested numerically for one-dimensional shock waves and one-dimensional Couette flow. The numerical scheme used here is based on Mieussens's discrete velocity model (DVM). Computational results from the kinetic models are compared to results obtained from the Direct Simulation Monte Carlo method (DSMC). It is found that for hard sphere molecules the results obtained from the two new kinetic models are very similar, and located in between the results from the ES-BGK and the v(C)-BGK models, while for Maxwell molecules the two new kinetic models are identical to the ES-BGK model. For one-dimensional shock waves, results from the new kinetic model II fit best with results from DSMC; while for one-dimensional Couette flow, the ES-BGK model is suggested. Also in the second part of the work, a modified numerical scheme is developed from Mieussens's original DVM. The basic idea is to use a linearized expression of the reference distribution function, instead of its exact expression, in the numerical scheme. Results from the modified scheme are very similar to the results from the original scheme for almost all done tests, while 20-40 percent of the computational time can be saved. In the third part, several sets of macroscopic continuum equations are examined for one-dimensional steady state Couette flow. For not too large Knudsen numbers (Knc=O.l) in the transition regime, it is found that the original and slightly linearized regularized 13 moment equations give better results than Grad's original 13 moment equations, which, however, give better results than the Burnett equations, while the Navier-Stokes-Fourier equations give the worst results, which is in agreement with the expectation. For large Knudsen number situations (Kn>O.l), it turns out that all macroscopic continuum equations tested fail in the accurate description of flows, while the Grad's 13 moment equations can still give better results than the Burnett equations.

No description available.

Thesis is submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Engineering and the Built Environment, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg, 2017 / Porous structures are increasingly becoming important engineering materials in aerospace, health, cooling of electronics, and several other areas. However, the supply of porous structures in these areas is still not being met because the conventional methods of manufacturing porous structures lack the modern requirements of competitiveness, quality, and exibility. Therefore, new meth- ods are required. One of these methods is the cold spray technology. However, studies do not give clear indications on how the cold spray technology could be used to fabricate porous structures. Consequently, this thesis uses various methods such as the control of cold spray parameters, powder mixtures, and the integration of the cold spray with alloy-de-alloy process to investigate the capability of cold spray technology to manufacture porous structures. The results of this investigation proved that the cold spray technology can be used to fabricate porous structures with varied amount of porosity for a number of applications. / MT 2018

No description available.

No description available.

Thesis (Ph. D.)--School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 2004. Directed by Carolyn Ruppel. / Vita. Includes bibliographical references (leaves 179-191).