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During a loss of coolant accident in a pressurised water reactor, emergency core cooling water is introduced via the downcomer annulus. The water may have to penetrate or overcome steam formed in the vessel due to the depressurisation. A typical counter-current flow situation can be created and dependent on the relative flow rates water may be prevented from reaching the reactor core with serious consequences. This,thesis considers the events leading up to this occurrence in a vertical, 54.75 mm diameter, 1 m long, stainless steel tube, to represent and provide a basic understanding of the situation occurring during a loss of coolant accident. Results are presented for air-water and steam-water flows with emphasis on the experimental and theoretical studies of the steam-water flow situation where direct contact heat transfer occurs. The air-water flooding data are shown to be well represented by a Wallis type flooding correlation. The steam-water flooding data are found to lie above the corresponding air-water data with their characteristic dependent on the water inlet subcooling. The percentage of the air/steam flow extracted with the water flow at the bottom porous sinter was found to exert a negative effect on the flooding phenomena. A theoretical model was developed to predict the liquid film thickness along the tube, and agreement with the experimental results demonstrated. A second theoretical model was developed to evaluate the temperature across the liquid film and along the test tube and from this model, the effective turbulent diffusivity was evaluated, leading to an estimate of the turbulent viscosity of the film under conditions in which substantial condensation took place. A semi-empirical model based on a linear stability analysis of a uniform liquid film and a counter-current flow of steam, was developed and modified for accelerating film flows. This model is shown to be capable of dealing with the steam-water flooding situation since reasonable agreement with the air-water flooding data is obtained. A modified Wallis type flooding correlation based on the experimental data, and accounting for non-equilibrium effect on flooding, is presented and discussed. A visualisation technique was developed and used to determine the flooding location in the section.

This study concerns the use of counter based laser Doppler anemometry in a wet steam flow of variable wetness fraction. Velocity measurements across the flow were made under different steam conditions. Comparison was made with a theoretical profile based upon a simple flow analysis. A small radial turbocharger was used as a means of extracting enthalpy homogeneously from a dry superheated flow of steam using the compressor as a brake. The wetness fraction of the exhaust was estimated using measured values of the thermodynamic properties. A laser extinction method was used to determine the number concentration and mean radius of the water droplets acting as natural scatterers in the wet steam. A laser anemometer was designed which made use of the properties of a propagating gaussian beam to produce a small probe volume. This was required to reduce the number of water droplets likely to be present simultaneously in the measuring volume. Good Doppler signals were obtained and these have been presented for a range of wet steam conditions. A computer model was developed to predict the scattering of laser light through wet steam. Results have shown that this can be accurately modelled using a particle size distribution function. The program written to perform the simulation takes into account both single and multiple scattering events. The parameters used for the distribution function required a knowledge of the wetness fraction and so provided a useful means of checking the estimate based upon the thermodynamic measurements. It has been demonstrated that the ability to obtain Doppler signals from the wet steam can be predicted by computation of the signal-to-noise ratio for the medium. Good results were obtained for the wet steam conditions under investigation.

A process for the production of clean hydrogen from methane based upon the sequential reduction and oxidation of metal oxides has been studied. The original process, based on iron oxide, suffers from significant disadvantages including deactivation by sintering and coke deposition. Improvement of the iron based system and identification and development of alternative metal oxides for hydrogen production has formed the basis of this study. The literature review outlines current methods for hydrogen production, followed by a review of the Steam-Iron Process as an improved and simpler method for clean hydrogen production. Thermodynamic assessment shows Fe3O4/FeO/Fe, WO3/WO2/W and SnO2/SnO/Sn to be the most prospective systems for the Steam-Metal Process. Experimental testing showed that Fe and W based systems were suitable for hydrogen production, but Sn based systems were unsuitable due to poor reducibility using methane. Attention was then focused on the addition of CeO2/ZrO2 promoters to Fe and W based systems in order to improve reactivity and prevent catalyst deactivation. CeO2/ZrO2 promoted Fe2O3 showed improved redox reactivity and increased stability, with formation of FeO. This aided in mitigation of sintering and introduced the possibility of prevention of coking, as catalysed by methane decomposition over fully reduced Fe metal. Although WO3 was found to be a suitable oxide, complete reduction to tungsten metal resulted in the formation of tungsten carbide and contamination of hydrogen produced. The formation of 31mol% [CeO2/ZrO2] / 69 mol% WO3 showed stabilised reduction using methane, allowing for redox cycling of the WO3-WO2 couple and preventing complete reduction to W metal. The use of the doped metal oxide showed the best performance of all the metal oxides tested, with clean hydrogen production over multiple redox cycles and high metal oxide stability. Further kinetic studies of both the reduction and oxidation reactions show reduction is chemical reaction controlled process (WO3/WO2.9 → WO2) with an apparent activation energy of 142 ?? 3 kJ/mol. Oxidation is also fitted to a chemically controlled process, with a reaction rate expression derived as: rH2 = [0.064 + (F x 0.00038)].e^(-108750/8.314xT).[PH2O]^(0.75) The apparent activation energy for oxidation was calculated as 109 ?? 1 kJ/mol.

A process for the production of clean hydrogen from methane based upon the sequential reduction and oxidation of metal oxides has been studied. The original process, based on iron oxide, suffers from significant disadvantages including deactivation by sintering and coke deposition. Improvement of the iron based system and identification and development of alternative metal oxides for hydrogen production has formed the basis of this study. The literature review outlines current methods for hydrogen production, followed by a review of the Steam-Iron Process as an improved and simpler method for clean hydrogen production. Thermodynamic assessment shows Fe3O4/FeO/Fe, WO3/WO2/W and SnO2/SnO/Sn to be the most prospective systems for the Steam-Metal Process. Experimental testing showed that Fe and W based systems were suitable for hydrogen production, but Sn based systems were unsuitable due to poor reducibility using methane. Attention was then focused on the addition of CeO2/ZrO2 promoters to Fe and W based systems in order to improve reactivity and prevent catalyst deactivation. CeO2/ZrO2 promoted Fe2O3 showed improved redox reactivity and increased stability, with formation of FeO. This aided in mitigation of sintering and introduced the possibility of prevention of coking, as catalysed by methane decomposition over fully reduced Fe metal. Although WO3 was found to be a suitable oxide, complete reduction to tungsten metal resulted in the formation of tungsten carbide and contamination of hydrogen produced. The formation of 31mol% [CeO2/ZrO2] / 69 mol% WO3 showed stabilised reduction using methane, allowing for redox cycling of the WO3-WO2 couple and preventing complete reduction to W metal. The use of the doped metal oxide showed the best performance of all the metal oxides tested, with clean hydrogen production over multiple redox cycles and high metal oxide stability. Further kinetic studies of both the reduction and oxidation reactions show reduction is chemical reaction controlled process (WO3/WO2.9 → WO2) with an apparent activation energy of 142 ?? 3 kJ/mol. Oxidation is also fitted to a chemically controlled process, with a reaction rate expression derived as: rH2 = [0.064 + (F x 0.00038)].e^(-108750/8.314xT).[PH2O]^(0.75) The apparent activation energy for oxidation was calculated as 109 ?? 1 kJ/mol.

Thesis (M.S.)--Ohio University, November, 1985. / Title from PDF t.p.

Thesis (M.S.)--Ohio University, November, 1987. / Title from PDF t.p.

Thesis (M.S.)--Virginia Polytechnic Institute and State University. / Vita. Abstract. Includes bibliographical references (leaves 130-136). Also available via the Internet.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: droplet injection; supersonic crossflow; superheat; droplet disruption. Includes bibliographical references (leaves 72-75).

Thesis (M.S. in Mechanical Engiineering)--Naval Postgraduate School, June 2009. / Thesis Advisor(s): Gannon, Anthony J. "June 2009." Author(s) subject terms: Computational Fluid Dynamics, Transonic, Compressor, Steam Ingestion, Sanger Rotor. Description based on title screen as viewed on July 10, 2009. Includes bibliographical references (p. 61). Also available in print.