No description available.

Thesis (MScIng)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis--Finland Institute of Technology. / Bibliography: p. [104]-105.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xi, 84 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (MTech(Chemical engineering))--Cape Technikon, Cape Town, 2000 / The demand for pool heating has increased dramatically over the last few years. This is ascribed to the idea that a swimming pool is expensive and can only be used for four months of the year. Therefore, a need for a relatively inexpensive solar heating system, capable of heating pool water to comfortable temperatures for an extended period, does exist. The least expensive solar heating system for swimming pool heating on the market in South Africa is in the order of R 11000. This is a fixed system, usually mounted on the roof of a house. In order to ensure the safety of minors, a safety net or sail must be installed. This is an additional cost, which approximates R1500, yielding a total cost for safety and heating in the order of R 12500. Copper pipes packed in black material are utilised in these conventional heating systems, and it is the cost of this good heat conductor that makes these units expensive. In this study an alternative pool heating system constructed of PVC was investigated. The system is designed to be flexible, mobile, act as a safety mechanism and absorbs the maximum amount of solar energy available. Dark blue material as opposed to black PVC was selected for aesthetic reasons at the expense of maximum efficiency. The material strength was tested as well as the strength of adhesion. The influence of factors such as exposure to the sun and the effect of water containing chlorine and acid on the material were evaluated. Also, various means of channelling the water through the system for increased efficiency was investigated. A pilot model was constructed and its performance evaluated. It has been concluded that the alternative approach provides effective heating at a lower cost than current systems. Also, the durability of the design was found to be acceptable.

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Absorption heat pump water heaters offer improved performance compared to conventional direct-fired water heaters, with the potential for coefficients of performance well in excess of 1. A primary energy usage comparison with electric heat pumps shows that absorption systems can be competitive with current technology. However, the implementation of these systems in the residential and light commercial market has not been practical for several reasons, including a limited knowledgebase on absorption systems for this application and the lack of compact and economically viable heat and mass exchangers. An improved understanding of the coupled heat and mass transfer processes in thermally driven absorption systems to be used as heat pump water heaters was obtained over the course of this study. In addition, microchannel heat and mass exchangers that enable such compact gas-fired heat pump water heaters were developed and tested. Performance at design and off-design conditions over a range of water and ambient temperatures was simulated in detail with a system-level model developed for this purpose. The system-level model was coupled with a water-tank model to investigate several water heating scenarios including a cold start, response to a medium sized draw and response to stand-by losses. Heat and mass exchangers were designed using component-level heat and mass transfer models. The heat and mass exchangers were first installed and evaluated on a breadboard test facility. Insights from these experiments were then used to design and fabricate a monolithic unit integrating several of the microchannel heat and mass exchangers, coupled with a gas-fired desorber heat exchanger to yield a stand-alone water heater prototype. The performance of the prototype was investigated over a range of water and ambient temperatures. A comparison of results was performed to investigate the deviation between model predictions and experimental values. A refined model was developed that more accurately predicted experimental results. Energy-use and cost analyses were performed and showed the potentially significant energy savings of thermally driven heat pump water heaters.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Experiments on several tokamaks convincingly demonstrated that a deliberate seeding of selected impurities can have a positive effect on the plasma performance. On the one hand, a significant reduction of the head load on divertor plates, one of the main concerns by constructing a thermonuclear reactor, has been achieved due to the increase of edge radiation. On the other hand, in some devices impurity seeding has led to an improvement of the energy confinement and the so called radiation improved (RI) mode has been established with the same or even better confinement than in the H-mode. However, in order to make use of these positive impacts, the behaviour of seeded impurity has to be strictly controlled and such negative developments as the accumulation of impurity ions in the plasma core accompanied by a strong increase of the central radiation losses should be avoided. Plasma heating by radio-frequency (RF) waves has been proven to be a useful tool to control the behaviour of puffed impurities. In order to asses the prospective of impurity control by RF waves in larger devices and under reactor conditions, proper modelling approaches have been developed. One of the important parameters, which should be evaluated, is the averaged energy or temperature of heated impurity ions. The latter determines, in particular, the power transported to the main species, and, thus, the heating efficiency. Besides, the temperature of impurity ions characterizes the intensity of particle losses for heated impurities. An approach to compute the impurity temperature under such conditions is elaborated. It is based on the construction of a hierarchy of approximate solutions to the impurity heat balance equation and takes into account that the density and, thus, the heat conductivity of heated ion species can change by many orders of magnitude with the position in the plasma. The developed method has been incorporated into 1D transport code RITM. Coupled with the full wave code TORIC, the particle and heat balances for impurity and main plasma species provide a self-consistent approach to model the ion cyclotron resonance heating (ICRH) scenario. The modelling of various heating scenarios for several tokamaks displays the impacts of impurity heating on the heat and particles transport and heating efficiency. To investigate the possibility of impurity control at the large tokamak the experiment on selective impurity heating in the mode conversion H/D plasma was prepared and carried out in the tokamak JET.