Dr. J. Sid Clements
Dr. J. Sid Clements of the Department of Physics and Astronomy had been conducting energy related research in applied electrostatics since 1980. One of his ongoing research projects involves the charging of high-resistivity aerosols by ions and/or electrons produced by corona discharge. The main applications of this research are electrostatic precipitation of pollutants and electrostatic painting.
Much of the the electricity in the United States is generated by extremely large (500 MW) coal-fired boilers which emit fly ash (coal and smoke ash as well as sulfur dioxide (SO2 and nitrogen oxides (NOx gases. The fly ash aerosols can be inhaled far into the lung, and the gases combine with water to form acid rain. Electrostatic precipitators (ESP) are commonly employed to collect the fly ash before it leaves the exhaust stack. The fly ash aerosols are charged by ions from a corona discharge, and an applied electric field causes them to move perpendicular to the air flow and collect on the walls (collecting plates) of the ESP. The layer of collected fly ash then falls into a hopper when the plates are rapped (vibrated by mechanical hammers). Fly ash collection efficiencies up to 99.999% can be achieved under ideal conditions.
Recently, utilities have begun burning low sulfur coal in order to reduce the emission of SO2. This lowers the cost of additonal pollution control equipment. Unfortunately, the fly ash from low sulfur coal has high electrical resistivity, which greatly lowers the performance of the ESP. Thus there is a need for research and development of methods for charging and collecting high resistivity fly ash.
Since coming to Appalachian in 1988, Dr. Clements has also been conducting research on electrostatic coating, specifically, in electrostatic painting of highly resistive plastic parts. Most automobiles and many appliances are painted electrostatically to improve the finish and reduce overspray (paint carried past the target by the air stream which results in wasted paint and air pollution). The liquid or powder paint is charged as it leaves the spray gun and an electric field is used to direct the charged liquid/powder to the grounded workpiece (target). For metal (conductive) targets, this results in an increased transfer efficiency and less overspray.
Recently, there has been a lot of interest in developing ways to paint plastic targets electrostatically because a large number of automobile body parts and appliance parts are now made from plastic. However, plastic targets can not be grounded, and the charged paint is repelled from the target as soon as the target becomes charged by ions from the gun. Therefore, current technology does not work for plastic targets unless they are first primed with a conductive coating and then grounded. This is an expensive drawback, and much work is now being done on ways to coat highly resistive plastic targets.