Heat and mass transfer between a surface and the surrounding gas can be enhanced by the application of electric body forces that induce jet or plume-like fluid motion. Such enhancement causes no noise or vibration, can be applied in complex, isolated geometries, and allows simple control of surface temperatures. This paper examines the potentially useful case of multiple fine-wire electrodes suspended in the open air above a grounded and heated horizontal surface. An infrared camera system was used to obtain a complete and accurate distribution of local heat transfer coefficients on the impingement surface. A numerical code was developed and verified by comparison with experimental data. This code was then used to investigate and compare the heat transfer generated by novel electrode geometries.

Corona wind enhancement of free convection was investigated with the needle-plate geometry in air. High voltage was applied to a needle suspended above a heated plate, and heat transfer coefficients were computed by measuring the plate surface temperature distribution with an infrared camera. Local heat transfer coefficients greater than 65 W/m2 K were measured, an enhancement of more than 25:1 over natural convection. The enhancement extended over a significant area, often reaching beyond the 30 cm measurement radius. At high power levels, Joule heating significantly reduced the effective impingement point heat transfer coefficient. The corona wind was found to be more efficient with positive potential than with negative. The heat transfer efficiency was optimized with respect to electrode height and applied voltage. The needle-plate heat transfer effectiveness improved rapidly with increasing height, and became relatively insensitive to height above a threshold value of about 5 cm.

No abstract

No abstract