The viscous oil-water hydrodynamics in a microchannel and phase equilibria of heavy oil and carbon dioxide gas have been investigated in connection with the enhanced recovery of heavy oil from petroleum reservoirs. The oil-water flow was studied in a circular microchannel made of fused silica with an I.D. of 250 µm. The viscosity of the silicone oil (863 mPa.sec) was close to that of the gas-saturated heavy oil in reservoirs. The channel was always initially filled with the oil. Two different sets of experiments were conducted: continuous oil-water flow and immiscible displacement of oil by water. For the case of continuous water and oil injection, different types of liquid-liquid flow patterns were identified and a flow pattern map was developed based on Reynolds, Capillary and Weber numbers. Also, a simple correlation for pressure drop of the two phase system was developed. In the immiscible displacement experiments, the water initially formed a core-annular flow pattern, i.e. a water core surrounded by a viscous oil film. The initially symmetric flow became asymmetric with time as the water core shifted off centre and also the waves at the oil-water interface became asymmetric. A linear stability analysis for core-annular flow was also performed. A characteristic equation which predicts the growth rate of perturbations as a function of the core radius, Reynolds number, and viscosity and density ratios of the two phases was developed. Also, two micro cells for gas solubility measurements in oils were designed and constructed. The blind cell had an internal volume of less than 2 ml and the micro glass cell had a volume less than 100 µl. By minimizing the cell volume, measurements could be made more quickly. The CO2 solubility was determined in bitumen and ashphaltene-free bitumen samples to show that ashphaltene has a negligible effect on CO2 solubility.

The flooding phenomenon can be defined as the maximum attainable flow condition beyond which the well defined countercurrent flow pattern can no longer exist. Thus the countercurrent flow limit (CCFL) or the flooding limit may be thought of as the flow condition at which the strong interaction between the two phases occurs. Considerable effort has been devoted to understanding and analyzing the flooding transition in many fields. For example; the flooding phenomenon is one of the important phenomena encountered in the safety analysis of light water reactors (pressurized water reactors and boiling water reactors). Accurate predictions of flooding behavior are particularly important in the assessment of emergency core cooling system (ECCS) performance. Currently, the postulated loss-of-coolant accident (LOCA) is considered the design basis accident. A physical understanding of the flooding phenomenon will help assess core refill during the course of a LOCA. Understanding the physical mechanisms of the flooding phenomenon might help establish more reliable equations and correlations which accurately describe the thermal hydraulic behavior of the system. The models can provide best-estimate capability to the design codes used in the evaluation of ECCS performance. The primary concern of this study was to: 1. Understand the physical mechanisms involved in the flooding phenomenon in order to derive a suitable analytical model. 2. Show that the combination of: a. Linear Instability Theory b. Kinematic Wave Theory c. Catastrophe Theory can provide a general model for flooding phenomenon. The theoretical model derived using the aforementioned combination of theories indicates good agreement between the experimental and the predicted values. Comparisons have been made using a large volume of air-water flooding data. / Graduation date: 1991

Mushroom (Agaricus bisporus) polyphenoloxidase (PPO) (EC 1.14.18.1) was isolated and purified using an aqueous two phase system composed of octyl phenol (ethyleneglycol) 7-8 ether (Triton X-114/TX-114). TX-114 is a non-ionic surfactant which thermoseparates in water and forms an aqueous two phase system with a surfactant-depleted top phase and a surfactant-enriched bottom phase. Critical micelle concentration (CMC) and cloud point of the surfactant are 0.17 mM and 22&ordm / C respectively. The partitioning behavior of mushroom PPO in water/TX-114 aqueous two-phase systems was studied and the effects of TX-114 concentration, ionic strength, pH, temperature and crude extract preparation on PPO partitioning were studied. PPO generally partitioned to the surfactant-depleted top phase / whereas many other hydrophobic proteins and molecules partitioned to the surfactantenriched bottom phase. When two-step ultrafiltration was used as a pretreatment, complete enzyme recovery was achieved with all studied TX-114 concentrations. Moreover, about 5 fold purification was achieved by using 8% TX-114. The purification increased to 10 fold by using polyvinylpolypyrolidone (PVPP) at pH 7.0 with a recovery of 72%. However changing pH from 7.0 to 6.0 increased the purification factor and enzyme recovery to 15 fold and 100%, respectively. Addition of potassium or sodium salts caused PPO molecules to partition in the surfactantenriched bottom phase. Finally, crude enzyme can be concentrated besides being purified and recovered by doing aqueous two-phase separation at room temperature.

The viscous oil-water hydrodynamics in a microchannel and phase equilibria of heavy oil and carbon dioxide gas have been investigated in connection with the enhanced recovery of heavy oil from petroleum reservoirs. The oil-water flow was studied in a circular microchannel made of fused silica with an I.D. of 250 µm. The viscosity of the silicone oil (863 mPa.sec) was close to that of the gas-saturated heavy oil in reservoirs. The channel was always initially filled with the oil. Two different sets of experiments were conducted: continuous oil-water flow and immiscible displacement of oil by water. For the case of continuous water and oil injection, different types of liquid-liquid flow patterns were identified and a flow pattern map was developed based on Reynolds, Capillary and Weber numbers. Also, a simple correlation for pressure drop of the two phase system was developed. In the immiscible displacement experiments, the water initially formed a core-annular flow pattern, i.e. a water core surrounded by a viscous oil film. The initially symmetric flow became asymmetric with time as the water core shifted off centre and also the waves at the oil-water interface became asymmetric. A linear stability analysis for core-annular flow was also performed. A characteristic equation which predicts the growth rate of perturbations as a function of the core radius, Reynolds number, and viscosity and density ratios of the two phases was developed. Also, two micro cells for gas solubility measurements in oils were designed and constructed. The blind cell had an internal volume of less than 2 ml and the micro glass cell had a volume less than 100 µl. By minimizing the cell volume, measurements could be made more quickly. The CO2 solubility was determined in bitumen and ashphaltene-free bitumen samples to show that ashphaltene has a negligible effect on CO2 solubility.

This study uses the Phase-field method to simulate the transient thermal current of the metal surface heated and molten by a massing energy. The flow field uses a two-dimension module, considered with the mass conservation equation, momentum equation, energy equation and level-set equation, to solve for the distribution in whole domain, including the interface, of temperature, velocity, pressure and level-set number. We ignore the effect of concentration diffusion, but consider about the effect of heat translation on the flow field. Finally the results will display the flows of air around molten area forced by buoyancy which is caused by high temperature, and the flows in molten area forced by thermocapillary which is caused by temperature gradient.

For energy conservation of sensorless two-phase half-wave brushless DC fan, this thesis develops a driver based on analogy circuits with current feedback control and speed feedback control. The main parts of the system include a sensorless start-up circuit, a sensorless commutation detection circuit, a speed feedback control circuit and a current feedback control circuit. Finally, we design experiments to compare it with outside PWM open-loop control and speed feedback control on experiment, the result shows that the driver with both current feedback control and speed feedback control displays better efficiency and lower vibration.

The design and implementation of speed control driver, which is applied to two-phase brushless DC fan motor is presented in this thesis. In addition, motor coils current limiter, output-stage Snubber circuit, and lock detection and auto-restart circuit are added to the driver for the sake of increasing stability and robustness. Because of high frequency energizing noise and dispensable power consumption problems generated by open-loop fixed frequency PWM speed control approach, several closed-loop speed control methods with speed estimation signal feedback are adopted for improvement. Furthermore, this thesis proposes a sensorless driving control strategy to eliminate Hall sensor in rotor position detection, and similarly has closed-loop speed control methods to achieve the goal of driver cost reduction, size decrease, and good control performance.

This thesis includes two topics. The first topic is a CMOS SRAM using dynamic threshold voltage wordline-transistors, which is focused on high speed applications. The second one is a high voltage generator for FLASH memories. The generated high voltages are applied to the wordline controlled transistors during access and verification operations. By taking advantage of the large current provided by low Vth and low leakage current provided by high Vth, a CMOS SRAM using dynamic threshold voltage wordline transistors is presented. The design of a 4-Kb SRAM is measured to possess a 2.2 ns access time, and consume 43.6 mW in the standby mode. The highest operating clock rate is estimated to be 667 MHz. A high voltage generator using 4 clocks with two phases is presented to provide a high voltage supply required by FLASH memories during programming mode and erase mode operations. The circuit is implemented by TSMC 0.25um 1P5M CMOS process. It can provide as high as +11.7 V and -11.6 V by given VDD=2.5 V.

Knowledge of the two-phase flow state is fundamental for two-phase flow system design and operation. In traditional two-phase flow studies, the flow regime refers to the physical location of the gas and liquid in a conduit. Flow configuration is important for engineering correlations of heat and mass transfer, pressure drop, and wall shear. However, it is somewhat subjective since it is mostly defined by experimental observation, resulting in an approximate and equivocal definition. Thus, there is need for a better, objective flow regime identification. The void fraction is a key parameter in monitoring the operating state of a two-phase system and several tools have been developed in order to measure it. The purpose of this study is to use the void fraction and other parameters of the system to achieve a model for flow pattern identification. Recently, an experimental program using the Foster-Miller two-phase flow test bed and Creare Inc. capacitance void fraction sensors was conducted in the microgravity environment of the NASA KC-135 aircraft. Several data types were taken for each phase, such as flow rate, superficial velocity, density and transient void fraction at 100Hz. Several analytical approaches were pursued, including a statistical approach of the fluctuation of the void fraction, Martinelli analysis, and Drift Flux analysis, in order to reach a model for flow pattern identification in microgravity conditions. Several parameters were found to be good flow pattern identifiers such as the statistical moments variance and skewness, Signal -to- noise ratio (SNR), Half Height Value (HHV) and Linear Area Difference (LAD). Moreover, relevant conclusions were achieved using the Martinelli parameter and the Drift Flux model in microgravity conditions. These results were compared with the basic literature.

An experimental study on drag reduction by injection of microbubbles was performed in the upper wall of a rectangular channel at Re = 5128. Particle Image Velocimetry measurement technique (PIV) was used to obtain instantaneous velocity fields in the x-y plane. Microbubbles, with an average diameter of 30??m, were produced by electrolysis using platinum wires with a diameter of 76 ??m. They were injected in the buffer layer producing several different values of local void fraction. A maximum drag reduction of 38.45% was attained with a local void fraction of 4.8 %. The pressure drop in the test station was measured by a reluctance pressure transducer. Several parameters such as velocity profile, turbulent intensities, skewness, flatness, joint probability density function (JPDF), enstrophy, one and two-dimensional energy spectra were evaluated. The results indicate that microbubbles reduced the intermittency of the streamwise fluctuating component in the region near the wall. At the same time they destroy or reduce the vortical structures regions (high shear zones) close to the wall. They also redistribute the energy among different eddy sizes. An energy shift from larger wavenumbers to lower wavenumbers is observed in the near wall region (buffer layer). However, outside this region, the opposite trend takes place. The JPDF results indicate that there is a decrease in the correlation between the streamwise and the normal fluctuating velocities, resulting in a reduction of the Reynolds stresses. The results of this study indicate that pursuing drag reduction by injection of microbubbles in the buffer layer could result in great saving of energy and money. The high wavenumber region of the one dimensional wavenumber spectra was evaluated from PIV spatial information, where the maximum wavenumber depends on the streamwise length (for streamwise wavenumber) of the recorded image and the minimum wavenumber depends on the distance between vectors. On the other hand, the low wavenumber region was calculated from the PIV temporal information by assuming Taylor??s frozen hypothesis. This new approach allows obtaining the energy distribution of a wider wavenumber region.