Date of Award
Doctor of Philosophy
An electrostatic suspension concept was successfully utilized in generating a uniform particulate cloud between two parallel electrodes in air at atmospheric pressure in order to investigate the effect of this cloud on electrical breakdown, electrical discharge, and ignition of combustible gases. Electrical breakdown was initiated by a fast moving injected needle electrode which resulted in a minimal disturbance of the suspension;It was observed that when using a negative needle (electrode), neither the breakdown voltage nor the needle position at breakdown depended significantly on the needle velocity or the particle number density. Conversely, the positive needle (electrode) breakdown voltage and needle position showed a strong dependence on these variables. Based on extensive experimental data of electrical breakdown in a uniform particulate suspension using a positive moving needle, an equation was satisfactorily correlated to the breakdown voltage, particle number density, particle diameter, and the point-to-plane and parallel electrode gap distances. This equation related two governing parameters, the electrode geometry and the particle collision probability. The collision probability is expected to determine the charge loss or charge interchange of pre-charged particles during collisions;It was also experimentally confirmed that the spark charge and/or the energy was nearly the same as that which was stored on the capacitors prior to breakdown, regardless of the presence of particles or the mode of discharge (fast single or double spark pulses, (TURN)10 nsec duration);It was discovered that the minimum ignition energy of a uniform inert particle-combustible gas mixture increased exponentially with a cubic power dependence on the particle surface area per unit volume of the mixture (or on the reciprocal of the interparticle distance based on its projected area). Also, the range of the fuel-air ratio for ignition decreased with an increase in the particle surface area per volume of the mixture, for a constant spark energy, and approached zero at a fuel-air ratio somewhat richer than stoichiometric;Applications of results from this study are relevant to further understanding of explosion hazard and electrical breakdown in high voltage systems associated with particulate clouds.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Yu, Tae-U, "Electrical breakdown and ignition of an electrostatic particulate suspension " (1983). Retrospective Theses and Dissertations. 7661.