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Vacuum arc thrusters offer a relatively simple and cheap form of satellite propulsion, especially suitable for nanosatellites such as CubeSats or even smaller. This thesis focuses on vacuum arc thruster design considering the thruster’s manufacturing, assembly and integration into the spacecraft, and proposes a new anode geometry easing thruster production. Vacuum arc thruster research is traditionally experimental in nature due to a lack of accurate models. This work follows this approach, and studies experimentally the effect of several geometric design parameters on thruster performance. The outcome confrms findings from several papers, and suggests specifc improvements towards existing models for predicting the effect of the thruster’s geometry on its thrust. The chosen experimental approach raised the need for a micro-thrust measurement stand. Two distinct measurement stands have been designed, realized and used to test various thruster prototypes. One test stand is more accurate. However, the other setup allows for considerably faster testing.

Yes / In this work, an artificial neural network (ANN) model based on the experimental data was developed to study the performance of vacuum membrane distillation (VMD) desalination process under different operating parameters such as the feed inlet temperature, the vacuum pressure, the feed flow rate and the feed salt concentration. The proposed model was found to be capable of predicting accurately the unseen data of the VMD desalination process. The correlation coefficient of the overall agreement between the ANN predictions and experimental data was found to be more than 0.994. The calculation value of the coefficient of variation (CV) was 0.02622, and there was coincident overlap between the target and the output data from the 3D generalization diagrams. The optimal operating conditions of the VMD process can be obtained from the performance analysis of the ANN model with a maximum permeate flux and an acceptable CV value based on the experiment.

Yes / This paper presents a simulation study of vacuum membrane distillation (VMD) for desalination. A simulation model was built on Aspen Plus® platform as user defined unit operation for VMD module. A simplified mathematical model was verified and the analysis of process performance based on simulation was also carried out. Temperature and concentration polarization effects are significant in the conditions of higher feed temperature and/or vacuum pressure. The sign of difference of the vapour pressures between at the membrane interfaces, is a pointer of the vacuum pressure threshold. Increasing the vacuum pressure at lower feed temperature is an effective way to increase the permeate flux and reduce the energy consumption simultaneously.

Further automation of the agricultural industry and an increase in organic fruit production are needed to address labor shortage and increased demand. The move to an autonomous bug vacuum is easier if the equipment is electric, and not powered by a tractor’s PTO (power take-off) shaft. The main objective of this project was to design a set of lygus bug vacuums to go on a robot that meets industry standards while using electric power instead of hydraulic. The frame of the vacuum was designed using the industry standard. While hydraulic systems have been a very effective power source for vacuums until now, electronic motors with VFD (variable frequency drive) control allow for a cost effective, precise control, of the lygus bug vacuums with less failures. This also allows a robot type system to be able to run the vacuums using a preexisting power source without the addition of a bulky hydraulic system.

This dissertation concerns the development of simulation and optimization technology for industrial, hydrolytic nylon-6 polymerizations. The significance of this work is that it is a comprehensive and fundamental analysis of nearly all of the pertinent aspects of simulation. It steps through all of the major steps for developing process models, including simulation of the reaction kinetics, phase equilibrium, physical properties, and mass-transfer- limited devolatization. Using this work, we can build accurate models for all major processing equipment involved in nylon-6 production. Contributions in this dissertation are of two types. Type one concerns the formalization of existing knowledge of nylon-6 polymerization mixtures, mainly for documentation and teaching purposes. Type two, on the other hand, concerns original research contributions. Formalizations of existing knowledge include reaction kinetics and physical properties. Original research contributions include models for phase equilibrium, diffusivities of water and caprolactam, and devolatization in vacuum-finishing reactors. We have designed all of the models herein to be fundamental, yet accessible to the practicing engineer. All of the analysis was done using commercial software packages offered by Aspen Technology, Cambridge, MA. We chose these packages for two reasons: (1) These packages enable one to quickly build fundamental steady-state and dynamic models of polymer trains; and (2) These packages are the only ones commercially available for simulating polymer trains. / Ph. D.

Understanding mechanisms at the molecular level is essential for interpreting and predicting the outcome of processes in all fields of chemistry. Insight into gas-surface reaction dynamics can be gained through molecular beam scattering experiments combined with classical trajectory simulations. In particular, energy exchange and thermal accommodation in the initial collision, the first step in most chemical reactions, can be probed with these experimental and computational tools. There are many questions regarding the dynamic details that occur during the interaction time between gas molecules and organic surfaces. For example, how does interfacial structure and density affect energy transfer? What roles do intramonolayer forces and chemical identity play in the dynamics? We have approached these questions by scattering high-energy, rare gas atoms from functionalized self-assembled monolayers. We used classical trajectory simulations to investigate the atomic-level details of the scattering dynamics. We find that approximately six to ten carbon atoms are involved in impulsive collision events, which is dependent on the packing density of the alkyl chains. Moreover, the higher the packing density of the alkyl chains, the less energy is transferred to the surface on average and the less often the incident atoms come into thermal equilibrium with the surface. In addition to the purely hydrocarbon monolayers, organic surfaces with lateral hydrogen-bonding networks create more rigid collision partners than surfaces with smaller inter-chain forces, such as van der Waals forces. Finally, we find some interesting properties for organic surfaces that possess fluorinated groups. For argon scattering, energy transfer decreases with an increasing amount of surface fluorination, whereas krypton and xenon scattering transfer most energy to monolayers terminated in CF₃ groups, followed by purely hydrocarbon surfaces, and then perfluorinated surfaces. / Ph. D.

Fried foods are popular around the world. They are also high in fat and considered unhealthy by many people. Reducing the fat content of fried food may allow for even more growth in their popularity, while allowing for healthier eating. Furthermore, vacuum-frying and frying with nitrogen gas have both been shown to extend the life of frying oil. In this study, the use of novel frying methods as a way to reduce fat content of breaded fried foods was evaluated. A pressure fryer was modified so that fish sticks could be vacuum-fried and fried using external gas (nitrogen and compressed air) as the pressurizing media. These products were compared to those pressure fried and fried atmospherically in terms of crust color, moisture content, oil content, texture, and juiciness. Overall, products fried using nitrogen and air were not found to be significantly different (p < 0.05) from each other. These products were both more tender and lower in oil content than steam-fried fish sticks. The energy to peak load of fish sticks fried with air was 123.10 J/kg, fish sticks fried with nitrogen had an energy to peak load of 134.64 J/kg, and fish sticks fried with traditional pressure frying had a peak load of 158.97 J/kg. The crust oil contents of fish sticks fried with air, nitrogen, and steam were 17.35%, 15.88%, and 23.31% oil by weight, respectively. In other words, using nitrogen or air to fry fish sticks reduced the fat uptake in the crust by 31.8% and 25.6% compared to traditional pressure frying, respectively. The only area where vacuum-frying had a significant effect, when compared to pressure-fried and atmospherically-fried fish sticks, was in juiciness. Vacuum-frying created significantly juicier fish sticks than the other two frying methods. Vacuum-fried fish sticks had juiciness of 43.03% (120oC) and 41.31% (150oC), while pressure-fried fish sticks had juiciness of 30.01% (175oC) and 32.93% (190oC), and atmospherically-fried fish sticks had juiciness of 31.56% (175oC) and 29.38% (190oC). In addition, vacuum-fried fish sticks were more tender than atmospherically-fried fish sticks. The results of this study demonstrated that frying with external pressurizing media can be used to reduce oil content in fish sticks, while also creating products that are more tender than conventionally pressure-fried fish sticks. In addition, vacuum-frying, which has been shown to extend oil life compared to pressure frying because of the lower temperatures involved, can be used to create fish sticks that are comparable to pressure-fried fish sticks, but juicier. / Master of Science

An adapted capacitance manometer is a sensor composed of one fixed plate and one movable plate that is able to make accurate pressure measurements in a low pressure environment. Using detection circuitry, a change in capacitance between the two plates can be measured and correlated to a differential pressure. First, a high sensitivity manometer is produced that exhibits a measurable change in capacitance when experiencing a pressure differential in a low pressure space environment. Second, an accurate and precise detection circuit is identified to measure the change in capacitance. Both, the manometer and the detection circuitry, are tested separately and together to confirm accurate measurements when experiencing small pressure differentials. The manometer shows low sensitivity at the desired differential pressure range but reacts predictably when compared to simulations. The manometer also shows an unexpected correlation in capacitance change to temperature change. / Master of Science

Copper and silver films of various thicknesses were deposited at a rapid rate, from four to twenty-five seconds, on glass substrates in ultra high vacua at pressures of 10⁻⁸ torr or lower. Their optical properties, reflectivity, transmissivity and absorptivity, were determined in vacua and in air by direct measurement using photomultiplier tubes. All the measurements were made at nearly normal incidence with a monochromatic light beam of wavelength 4358 A. It was found that the reflectivity of films of both copper and silver decreased as they were exposed to air. The change took place in equal steps. Under the same circumstances, transmissivity increased but in a less regular way. Absorption changed in a most irregular fashion; no pattern could be established. From this study of optical properties, the layer formation on fresh, clean surfaces of copper and silver caused by the air molecules was quite evident. In the case of copper, there may be one or two layers depending on the thickness of the film. They are formed primarily by cuprous oxide. In the case of silver the layer was attributed to chemisorption. Even though there was some indication that more than one layer was formed, the evidence was not conclusive. / Master of Science