Effects of Nozzle and Grid Acceleration of Corona Wind on Cooling of a Vertical Flat Plate

摘要

Several experiments were conducted to determine the effect of nozzle and grid acceleration of a corona wind on the free convection heat transfer rate of a vertically mounted heated flat plate. The plate was maintained at ground potential and was suspended in a Mach-Zehnder interferometer. A positively charged stretched wire emitter and 19 point emitter were used. Baseline tests were conducted to determine the changes in plate convective heat transfer rate attainable at various field power settings, and plate-to-emitter distances. A two dimensional variable area convergent nozzle constructed of wood and plexiglas was used to accelerate the flow of the corona wind toward the plate. Nozzle inlet/exit area, plate-to-nozzle distance and plate-to-emitter distance was varied. A grid accelerator composed of an aluminum screen mesh was attached across the exit area of the convergent nozzle and was maintained at ground potential. Plate heat transfer rates were determined from energy balance measurements and interferometer photographs. Results indicated that the nozzle and grid accelerator coupled with either emitter did not improve upon overall plate heat transfer rates obtained in baseline tests. On the contrary, heat transfer rates for individual plate sections were improved using the multipoint emitter and nozzle. (Author)