Thesis (M. Phil.)--University of Hong Kong, 1987.

The calculation of the physical conditions near the inner rim of a protoplanetary disk using the new computational model Pisco is described. Diagnostic plots illustrate solutions for disk structure, radiation field, chemical composition, and heating and cooling of the disk in a steady-state approximation for both disks with unsettled dust and with settled dust. Disks with unsettled dust are found to have hotter gas temperatures above the disk photosphere and a more pronounced temperature inversion at the disk photosphere. Recommendations are made for the development of Pisco. Pisco has the potential to explore what observed molecular emission can imply about disk structure. / text

This study focused on the improvement of film cooling for gas turbine vanes using both computational and experimental techniques. The experimental component used a matched Biot number model to measure scaled surface temperature (overall effectiveness) distributions representative of engine conditions for two new configurations. One configuration consisted of a single row of holes on the pressure surface while the other used numerous film cooling holes over the entire vane including a showerhead. Both configurations used internal impingement cooling representative of a 1st vane. Adiabatic effectiveness was also measured. No previous studies had shown the effect of injection on the mean and fluctuating velocity profiles for the suction surface, so measurements were made at two locations immediately upstream of film cooling holes from the fully cooled cooling configuration. Different blowing conditions were evaluated. Computational tools are increasingly important in the design of advanced gas turbine engines and validation of these tools is required prior to integration into the design process. Two film cooling configurations were simulated and compared to past experimental work. Data from matched Biot number experiments was used to validate the overall effectiveness from conjugate simulations in addition to adiabatic effectiveness. A simulation of a single row of cooling holes on the suction side also gave additional insight into the interaction of film cooling jets with the thermal boundary layer. A showerhead configuration was also simulated. The final portion of this study sought to evaluate the performance of six RANS models (standard, realizable, and renormalization group k-ε; standard k-ω; k-ω SST; and Transition SST) with respect to the prediction of thermal boundary layers. The turbulent Prandtl number was varied to test a simple method for improvement of the thermal boundary layer predictions. / text

In the United States, natural gas turbine generators account for approximately 7% of the total primary energy consumed. A one percent increase in gas turbine efficiency could result in savings of approximately 30 million dollars for operators and, subsequently, electricity end-users. The efficiency of a gas turbine engine is tied directly to the temperature at which the products of combustion enter the first stage, high-pressure turbine. The maximum operating temperature of the turbine components’ materials is the major limiting factor in increasing the turbine inlet temperature. In fact, current turbine inlet temperatures regularly exceed the melting temperature of the turbine vanes through advanced vane cooling techniques. These cooling techniques include vane surface film cooling, internal vane cooling, and the addition of a thermal barrier coating (TBC) to the exterior of the turbine vane. Typically, the performance of vane cooling techniques is evaluated using the adiabatic film effectiveness. However, the adiabatic film effectiveness, by definition, does not consider conjugate heat transfer effects. In order to evaluate the performance of internal vane cooling and a TBC it is necessary to consider conjugate heat transfer effects. The goal of this study was to provide insight into the conjugate heat transfer behavior of actual turbine vanes and various vane cooling techniques through experimental and analytical modeling in the pursuit of higher turbine inlet temperatures resulting in higher overall turbine efficiencies. The primary focus of this study was to experimentally characterize the combined effects of a TBC and film cooling. Vane model experiments were performed using a 10x scaled first stage inlet guide vane model that was designed using the Matched Biot Method to properly scale both the geometrical and thermal properties of an actual turbine vane. Two different TBC thicknesses were evaluated in this study. Along with the TBCs, six different film cooling configurations were evaluated which included pressure side round holes with a showerhead, round holes only, craters, a novel trench design called the modified trench, an ideal trench, and a realistic trench that takes manufacturing abilities into account. These film cooling geometries were created within the TBC layer. Each of the vane configurations was evaluated by monitoring a variety of temperatures, including the temperature of the exterior vane wall and the exterior surface of the TBC. This study found that the presence of a TBC decreased the sensitivity of the thermal barrier coating and vane wall interface temperature to changes in film coolant flow rates and changes in film cooling geometry. Therefore, research into improved film cooling geometries may not be valuable when a TBC is incorporated. This study also developed an analytical model which was used to predict the performance of the TBCs as a design tool. The analytical prediction model provided reasonable agreement with experimental data when using baseline data from an experiment with another TBC. However, the analytical prediction model performed poorly when predicting a TBC’s performance using baseline data collected from an experiment without a TBC. / text

Film cooling computations and experiments were performed to study heat transfer and adiabatic effectiveness for several geometries. Various assumptions commonly made in film cooling experiments were computationally simulated to test the validity of using these assumptions to predict the heat flux into conducting walls. The validity of these assumptions was examined via computational simulations of film cooling on adiabatic, heated, and conducting flat plates using the commercial code FLUENT. The assumptions were found to be reasonable overall, but certain regions in the domain suffered from poor predictions. Film cooling adiabatic effectiveness and heat transfer coefficients for axial holes embedded in a 1 [hole diameter] transverse trench on the suction side of a simulated turbine vane were experimentally investigated as well to determine the net heat flux reduction. Heat transfer coefficients were determined with and without upstream heating both with and without a tripped boundary layer approach flow. The net heat flux reduction for the trench was found to be much higher than for the baseline row of holes. Two transverse trench geometries and a baseline row of holes geometry were also simulated using FLUENT and the results were compared to experiments by Waye and Bogard (2006). Trends between simulated trench configurations and baseline cylindrical holes without a trench were found to be largely in agreement with experimental trends, suggesting that FLUENT can be used as a tool for studying new trench configurations. / text

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We measure inelastic cross sections for atomic thorium (Th) and molecular thorium monoxide (ThO) in collisions with $^3$He at temperatures near 1 K. We determine the Zeeman relaxation cross section for Th ($^3$F$_2$) to be $\sim 2 \times 10^{-17}$~cm$^{-2}$ at 800~mK. We study electronic inelastic processes in Th ($^3$P$_0$) and find no quenching even after $10^6$ collisions at 800~mK. We measure the vibrational quenching cross section for ThO~(X,~$\nu=1$) to be $(7.9 \pm 2.7) \times 10^{-19}$~cm$^{-2}$ at 800~mK. Finally, we observe indirect evidence for ThO (X, $\nu=0$)--$^3$He van der Waals complex formation, and measure the 3-body recombination rate constant to be $\Gamma_3 = (8 \pm 2) \times 10^{-33}$~cm$^6$s$^{-1}$ at 2.4~K. The stability of the ground Th ($^3$F$_2$) state, metastable Th ($^3$P$_0$) state, and vibrational excited ThO (X, $\nu=1$) state provides data on anisotropic interactions in new systems and opens up the possibility for further studies and experiments, including trapping. / Physics

This dissertation details the development and implementation of novel experimental techniques for cooling neutral atoms. Based on a method first proposed by Maxwell in a nineteenth century thought experiment, these techniques reduce the entropy of an ensemble by allowing unidirectional transmission through a barrier and thus compressing the ensemble without doing work or increasing its temperature. Because of their general nature, these techniques are much more broadly applicable than traditional laser and evaporative cooling methods, with the potential to cool the vast majority of the periodic table and even molecules. An implementation that cools in one dimension is demonstrated for an ensemble of magnetically trapped rubidium atoms which are irreversibly transferred to a gravito-optical trap. Analysis of the experimental results confirms that phase-space is completely compressed in one dimension. The results also indicate that the overall cooling performance is limited only by the dynamics of atoms in the magnetic trap and may be improved with a more ergodic system. Three-dimensional cooling may be accomplished with a modified technique which substitutes a radio-frequency-dressed magnetic trap for the gravito-optical trap. Application of this technique to atomic hydrogen and progress toward building an experimental apparatus are discussed. / text

No description available.

This thesis presents a thermodynamic model for a screw chiller and cooling tower system for the purpose of developing an optimized control algorithm for the chiller plant. The thermodynamic chiller model is drawn from the thermodynamic models developed by Gordon and Ng (1996). However, the entropy production in the compressor is empirically related to the pressure difference measured across the compressor. The thermodynamic cooling tower model is the Baker & Shryock cooling tower model that is presented in ASHRAE Handbook - HVAC Systems and Equipment (1992). The models are coupled to form a chiller plant model which can be used to determine the optimal performance. Two correlations are then required to optimize the system: a wet-bulb/setpoint correlation and a fan speed/pump speed correlation. Using these correlations, a "quasi-optimal" operation can be achieved which will save 17% of the energy consumed by the chiller plant.