UC Davis

Esohe (Kristen) Fawole915549685

Corona and Coffee: Charge Phenomena in High Voltage Electrophoresis and the Impact of Using Coffee to Teach Chemical Engineering to Non-STEM Students

This dissertation is split into two objectives: (1) to better understand the effect of relative humidity (RH) on charge transfer between metal electrodes and water droplets and (2) to assess the impact of The Design of Coffee, a general education, introductory chemical engineering course, on non-STEM students’ ability to understand fundamental chemical engineering principles and the impact of the course on their decision to major in STEM disciplines.(1): When immersed in an insulating fluid subjected to a high voltage electric field, charged droplets will exchange charge via contact with each electrode and move in an oscillatory motion between the electrodes. Traditionally, this induced motion has been used to drive droplet coalescence in electrostatic dehydrators and, more recently, microfluidic devices. The measurement of charge acquired by the droplet is of fundamental interest as the charge determines the coalescence behavior, direction, and magnitude of movement. Extant theory for the charge a droplet or metal particle acquires considers only the electric properties of the conducting sphere and the surrounding insulating fluid, however, there are important reasons to suspect that the ambient humidity might play a role. The charge dynamics of a metal clip-metal electrode pair and the droplet HV apparatus were examined for different conditions. At sufficient humidity levels, the expected capacitive charge is followed by an increase charge. The excess charge persists after removing the applied voltage and physically removing the electrode from the Faraday cup. The results are interpreted in terms of a corona-onset, water ionization mechanism where water molecules are ionized by collision and the resulting ion’s drift gives rise to a continuous unipolar current measured by the nanocoulombmeter. (2): Typical introductory engineering classes require students to have prior knowledge of advanced concepts and are often lecture-based, supplemented with discussions or presentations. While these activities offer students exposure to the engineering discipline, they lack the hands-on component commonly used to enhance learning. At UC Davis, The Design of Coffee is a popular general education course offered by the Department of Chemical Engineering that uses the roasting and brewing of coffee to teach chemical engineering principles to a broad audience. Freshman design courses, like The Design of Coffee, use comprehensive teaching strategies to challenge students to innovate and have been proven to be more effective in engaging and inspiring diverse students in STEM majors. We hypothesized that first-year non-STEM students taking The Design of Coffee would be more likely to change into STEM majors due to the course’s experiential and approachable nature as compared to first-year non-STEM students that took a comparable introductory food science course. To test this hypothesis, we performed a detailed statistical analysis comparing the two groups. At least 12 students were found to have changed their major into chemical or biochemical engineering after taking The Design of Coffee. Statistical analyses of achievement in the fluid mechanics laboratory module were conducted as well. We measured gains in comprehension using quizzes administered before and after the lab session and we assessed students’ ability to communicate and interpret technical data by comparisons of submitted lab reports versus a standardized rubric.