ETD Collection

Permanent URI for this collectionhttps://wiredspace.wits.ac.za/handle/10539/104


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    Fabrication of porous structures using cold gas dynamic spray technology
    (2017) Hamweendo, Agripa
    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.
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    Application of population balance models to the study of nucleation and growth of bubbles produced at gas evolving electrodes
    (2015-08-06) Hofman, David Lester
    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