Texas A&M University
Professor David Staack
Dr. Yevgeny Raitses collaborates with Professor David Staack of TAMU Mechanical Engineering Department on discharges in liquids. This new research topic is relevant to energy, environmental and medical applications. This is why the research in this area has attracted a significant attention from industry and government agencies. Prof. Staack is a junior faculty of TAMU, who is already considered as one of the leading researchers in this field. His research is focused mainly on plasma chemistry and application aspects of discharges in liquids. The PPPL’s support of the last year helped Prof. Staack to advance understanding of plasma science associated with these discharges. OSUR supported travel for Prof. Staack and his graduate student, Grant Gaalema, to PPPL and provided a high frame rate Phantom V7.3 camera for high-speed imaging and characterization of water bubble dynamics and electrical breakdown in water-oil mixtures.
System Description and Experiments
The system of interest is depicted in Fig. 1, which shows several discharges between an array of water droplets suspended in insulating oil between a high voltage and a grounded electrode. The mineral oil used is clear and water droplets are dyed blue for visualization. The upper electrode is powered at about 15 kV DC, and the lower electrode is grounded. Current can be as much as 1 mA during a discharge, but is nominally less than 10 uA. Inter-electrode spacing is about 3 cm. Water with conductivity similar to tap water are used, acts as the charge carrier and as a deformable conductor bridging the gap between the powered and grounded electrodes. Gravity acts downwards and without an applied electric field the water droplets fall to the bottom. With an applied field electric forces pull the charged water droplets up and down (depending on their charge) and they bounce between the electrodes. With sufficiently high electric field the water droplets self-align between the electrodes with small oil gaps between them. Electric fields are sufficiently high between the water droplets to cause electrical breakdown of the oil.
The purpose of the experiments at PPPL was to use the fast frame rate camera to capture with high temporal and spatial resolution the dynamics of the bubbles and discharges. Specifically they sought to categorize observable behaviors such as the breakdown sequence of events and provide quantitative information on bubble motion, discharge duration and discharge dynamics. Bubble position as a function of time, applied electric field, along with bubble size can be used for estimates of electric forces and charging of the bubbles. The location and shape of bubbles can be used to estimate the breakdown field strength of the oil.
