The experimental formation of natural gas hydrate on pendant water droplet exposed to natural gas was conducted and visually observed under the pressures from 3.86MPa to 6.05MPa. The temperature was set at 274.75K and 273.35K. The diameter of the pendant water droplet was around 4mm. The nucleation and growth of hydrate film on the pendant water drop exhibited a generalized trend. The film initially generated at the boundary between the water drop and suspension tube, and afterwards grew laterally and longitudinally on the surface of the water drop. The phenomenon of the two layers of hydrate films growing on the pendant water drop distinguished from the experiments on the sessile water drop. The effect of the driving force that resulted from the overpressure from the three equilibrium pressure on the hydrate nucleation and growth was investigated. It was found that the elevation of the driving force reduced the nucleation time and shortened the process of the hydrate growth on the pendant water drop. The crystals on the hydrate shell became coarser with the increase of the driving force. The mechanism for the hydrate film formation and growth on static pedant water droplet included four stages, such as nucleation, generation of the hydrate film, growth of the hydrate film, and hydration below the hydrate shell.

After reviewing the documents about the studies of hydrate formation kinetics in the world, this paper analyzed the process of hydrate formation on a suspended water droplet, which was based on the hydrate formation with water spay method, proposed a corresponding mathematical model, and solved it. Afterwards, the discussion about this model was presented. The results indicated that equilibrium time diminished with the decrease of the water droplet radius, and prolonged with the increase of sub-cooling degree, the reaction time for the second period reduced with the increase of subcooling degree, but was free from the effect of the variation of the water droplet size. The first period of the hydration on the water droplet was quite short, while the second period was considerably longer. Therefore, shortening the duration time of the second period of hydration was obviously able to accelerate the hydrate formation on the water droplet.

abstract: High Voltage Direct Current (HVDC) technology is being considered for several long distance point-to-point overhead transmission lines, because of their lower losses and higher transmission capability, when compared to AC systems. Insulators are used to support and isolate the conductors mechanically and electrically. Composite insulators are gaining popularity for both AC and DC lines, for the reasons of light weight and good performance under contaminated conditions. This research illustrates the electric potential and field computation on HVDC composite insulators by using the charge simulation method. The electric field is calculated under both dry and wet conditions. Under dry conditions, the field distributions along the insulators whose voltage levels range from 500 kV to 1200 kV are calculated and compared. The results indicate that the HVDC insulator produces higher electric field, when compared to AC insulator. Under wet conditions, a 500 kV insulator is modeled with discrete water droplets on the surface. In this case, the field distribution is affected by surface resistivity and separations between droplets. The corona effects on insulators are analyzed for both dry and wet conditions. Corona discharge is created, when electric field strength exceeds the threshold value. Corona and grading rings are placed near the end-fittings of the insulators to reduce occurrence of corona. The dimensions of these rings, specifically their radius, tube thickness and projection from end fittings are optimized. This will help the utilities design proper corona and grading rings to reduce the corona phenomena. / Dissertation/Thesis / M.S. Electrical Engineering 2013

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This thesis focuses on the study of water transportation on vehicle surfaces, which is crucial for ensuring the unobstructed operation of sensors and cameras in autonomous vehicles. The research aims to develop and validate experimental and simulation methods to enhance the understanding of water droplet behaviour and to create accurate models for computational fluid dynamics (CFD) simulations. The primary objective is to investigate the feasibility of simulating water droplets using CFD. The study examines the behaviour of water droplets on a lacquered metal sheet and a glass surface. Physical experiments and CFD simulations are conducted to analyse droplet movement under the influence of gravity and airflow. The findings provide insights into the factors influencing droplet behaviour and validate the accuracy of the simulation models through physical tests. The research also discusses the limitations of the study and the implications for Volvo Cars, aiming to improve their ability to predict water droplet movement on their vehicles. / Denna avhandling fokuserar på studien av vattentransport på fordonssytor, vilket är avgörande för att säkerställa att sensorer och kameror i autonoma fordon kan fungera utan hinder. Forskningen syftar till att utveckla och validera experimentella och simuleringsmetoder för att förbättra förståelsen av vattendroppars beteende och skapa noggranna modeller för simuleringar inom beräkningsfluidmekanik (CFD). Det primära målet är att undersöka möjligheten att simulera vattendroppar med hjälp av CFD och deras påverkan på fordonssytor. Studien undersöker beteendet hos vattendroppar på en lackerad metallplåt och en glasyta med varierande lutningsvinklar. Fysiska experiment och CFD-simuleringar utförs för att analysera dropparnas rörelse under påverkan av tyngdkraft och luftström. Resultaten ger insikter om de faktorer som påverkar dropparnas beteende och validerar modellernas noggrannhet genom fysiska tester. Forskningen diskuterar även studiens begränsningar och dess implikationer för Volvo Cars, med målet att förbättra deras förmåga att förutsäga vattendroppars rörelse på deras fordon, vilket leder till effektivare vindtunneltester och säkrare fordon.

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