Pool boiling process is frequently encountered in a number of engineering applications. It is difficult to exactly predict the heat transfer coefficient. This is because the boiling phenomenon is rather complex and influenced by many factors, such as surface condition, heater size, geometry, material, arrangement of heated rods, and refrigerants, etc. The key boiling parameters (bubble dynamics data) such as bubble departure diameter, frequency, velocity and nucleation site density will be varied in such different heated surface resulting in the different effect of heat transfer. Furthermore, more fundamental of the physical phenomenon can be obtained. This study was performed experimentally. R-134a and R-600a were used as refrigerants. The surface condition will be changed with plasma spray coating. It is expected that the surface condition can affect the nucleate boiling heat transfer in certain degree. In addition, using the high speed digital vide camera and LDV to measure the bubble diameter and dynamics of R-600a and R-134a while growing. According of the results of experiments. The boiling curves in different situation were drawn and the influences of heat transfer coefficients by bubble velocity was also examinate. Finally, to broaden our basic understanding of different characteristics of refrigeration surface condition and heat transfer coefficient, thermal design data of a flooded type evaporator of high performance as well as more and further physical insight of the above-stated nucleate boiling heat transfer can be acquired. The results will hopefully be helpful not only for the academia but for the industry.

Thesis (Ph. D.) in Chemical Engineering--University of Maine, 2000. / Includes vita. Includes bibliographical references (leaves 129-134).

Thesis (Ph. D.) in Chemical Engineering--University of Maine, 2001. / Includes vita. Advisory Committee: William N. Unertl, Prof. of Physics, Co-Advisor; Douglas W. Bousfield, Prof. of Chemical Engineering, Co-Advisor; Vincent Caccese, Prof. of Mechanical Engineering; Albert Co, Prof. of Chemical Engineering; Nick Triantafillopoulos, Adjunct Prof. of Chemical Engineering, OMNOVA Solutions. Includes bibliographical references (leaves 149-157).

No description available.

This thesis is concerned with the production of metal-coated optical fibres, the fibres being drawn within a vacuum. Most common methods for producing optical fibres employ an oxy-gas ring burner or an inert gas resistance furnace to reach the high temperatures necessary to melt silica. These methods have the disadvantage of exposing the molten or hot silica fibre to the atmosphere before a protective coating is applied, thereby increasing the possibility of contaminants being present at the fibre surface. A novel though more elaborate method of producing fibres is described, with preliminary experimental results. Vacuum production allows the fibre to be metal-coated, using a magnetron sputtering technique, before exposure to the atmosphere, and the methods by which this is achieved are described. An electromagnetically operated optical fibre switch utilising a ferromagnetically-coated optical fibre is also described.

Methods of reactive magnetron sputtering using the sequential oxidisation of a sputtered metal film from two magnetron sources, in a rotating substrate system, have been developed. A rotation rate of around one revolution per second enhanced atomic level mixing of the film constituents on the substrate. Depending on the materials involved, two very fast feedback methods were employed to automatically control the admission rate of oxygen into the sputtering system. These methods were plasma emission monitoring (PEM), which was used to control the reactive sputter-deposition of In, Zn, W, V, Mo and Ti oxide, and voltage control, which was used to control the reactive sputter-deposition of Zn, Cu, Pb and Al oxide. The stoichiometry of the film was controlled by PEM or voltage control on one magnetron, and dopants were added by sputtering from the other magnetron. In other words, the former magnetron served two purposes; the first was to sputter metal and oxidise it, and the second purpose was to oxidise the metal sputtered from the other magnetron.

No description available.

The properties of functional materials have been studied with density functional theory. The first type of materials that have been investigated is the so called diluted magnetic semiconductors. It is a new class of materials that could offer enhanced functionality by making use of spin in addition to the charge of the electron. (Mn,Al) co-doped ZnO has been investigated regarding the Al significance on ferromagnetic behavior using density functional theory within the generalized-gradient approximation plus on-site Coulomb interaction. Despite the presence of Al the system always shows antiferromagnetic behavior. The role of intrinsic defects on ferromagnetism in pure and Cr doped In2O3 was also studied. For pristine In2O3, In vacancy and O interstitial states are completely spin polarized. Moreover, these hole states will create Cr ions in mixed valence state, giving rise to a strong ferromagnetic coupling. The second type of functional materials studied are hydrogen storage materials for mobile applications. These materials are considered as alternative if hydrogen is to replace fossil fuels as a energy carrier. In the view of this a series of compounds containing boron, nitrogen and hydrogen has been examined with respect to electronic structure, dehydrogenation energy and hydrogen diffusion properties. One compound, NH3BH3, has many desirable properties as a hydrogen storage material. In an effort to improve those properties, one of the H atoms in the NH3 group was replaced by Li, Na or Sr. The calculated hydrogen removal energies of the hydrogen release reactions were found to be significantly improved. Finally, a coating material, Al2O3, for wear resistant coatings on high performance cemented carbide cutting tools has been investigated. Chemical vapor deposition grown Al2O3 has been used for decades by the industry. To improve the growth process H2S is added to the gas mixture. The catalytic effect of H2S on the AlCl3/H2/CO2/HCl chemical vapor deposition process has been investigated on an atomistic scale. By applying a combined approach of thermodynamic modeling and density functional theory it seems that H2S acts as mediator for the oxygenation of the Al-surface which will in turn increase the growth rate of Al2O3.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 83-87). Also available on the World Wide Web.