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Thesis (MTech(Electrical engineering))--Cape Technikon, Cape Town, 2000 / The development of an automatic frequency control system for a miniature high frequency induction furnace is described. A background study into the fields of induction-heating, resonance, power electronic resonant converters and phase locked-loops are performed with relevance to this research. An analysis of the resonant load circuit is performed by means of a combination of measurement and numerical simulations. The study of the load behavior and power source is used as a :001 to aid effective implementation of the automatic frequency control system. This Jimulation data is used to detenninc the operating frequency range of the RLL system. A background study is performed in whieh several frequency-control schemes for power electronic converters are investigated. A brief summary, in which the basic requirements for a frequency control system with regards to this research are presented. Two revisions of the Automatic Frequency Control system (RLL) were implemented, on the induction furnace. Experimental results on both systems (Revl and Rev2), illustrating the necessity for frequency control are also presented. Future suggestions for optimizing the loop performance are presented. Further steps in the developmental process of the miniature high frequencj induction furnace are also discussed.

Please read the abstract in the section, 00front of this document / Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / MEng / unrestricted

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Current water-cooling technology used in the metallurgical industry poses a major safety concern. In addition, these systems are expensive to operate and result in significant energy losses. / The purpose of the research presented in this thesis was to develop a viable cooling system based on novel heat pipe technology which addresses these problems. This technology employs boiling as the means to store and transfer heat energy. The large heat extraction capacity of the device is owed to two design features: firstly, a separate return line that generates a column of liquid working fluid which drains into the evaporator by gravity, and secondly, a helical flow modifier in the evaporator that stabilizes annular two-phase flow. / A full-scale copper tapblock and launder were designed with water-based heat pipe cooling systems. These systems were successfully tested under industrial heat loading conditions, using a gas burner to simulate the heat loads. / The tapblock cooling system was able to dissipate 142 kW per heat pipe, at heat fluxes as high as 2.4 MW/m2. These values are the largest to date using the novel water-based heat pipe technology. The launder system was the first to incorporate horizontal heat pipes, as well as have multiple evaporators feeding a single condenser. / The cooling systems used in both experiments were fundamentally safer than watercooling systems, being operated at low pressures and with only several kilograms of water exposed to the heat source. The cooling water requirements of these systems represent a reduction of 80-95% compared to conventional water-cooling, with increased potential for energy recovery. / During the testing, dry-out and film boiling were identified as the main limitations. It was found that film boiling occurs when the flow in the evaporator is not great enough to generate a helical motion. The dry-out limitation was achieved when the velocity of the flow within the evaporator was too great, causing a large pressure gradient that opposes the gravity head of the return line. / Both of these limitations are related to the configuration of the evaporator, i.e. the return line and the flow modifier. A methodology was developed to model the evaporator numerically using computational fluid dynamics. This methodology can be used to understand how the design parameters of the evaporator affect the flow patterns during operation.

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