Heat Transfer and Flow Characteristics of Two-Dimensional Jets Impinging on Heated Protrusions With Crossflow of the Spent Air

Abstract

The flow structure and local heat transfer characteristics of two-dimensional slot jets impinging on heated protrusions has been investigated. The spent air was constrained to exit at one end of the channel, forming a crossflow. The effects of three parameters on the heat transfer were examined for an array of five protruding heat sources. They include the jet slot width, distance between the jet exit and the protrusion, and the average jet Reynolds number. Laser-Doppler velocimeter measurements were made to detail the mean and turbulent flow structure in the channel. Experimental results reveal that the flow and heat transfer are dominated by turbulent transport even for Reynolds numbers as low as 300. Two transport mechanisms were identified affecting the heat transfer. The first was jet impingement, the second being crossflow of the spent air. A complex interaction between the two mechanisms was observed. At low nozzle-protrusion spacing with large slot jets the heat transfer was dominated by the crossflow, whereas for high nozzle-protrusion spacing and small jets, transport was dominated by jet impingement. It is postulated that the highest average Nusselt number occurs when the jets and the crossflow influence act with near-equal intensity.