衝突噴流熱伝達とその流れ挙動に及ぼすオリフィス形状の影響

概要

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Impingement jet is widely used in industrial fields because it provides a high heat transfer coefficient near the stagnation region. However, few methods exist to control the impingement heat transfer. Recently, peculiar diffusion process “axis-switching” in three dimensional free jet has been reported, and the possibility of axis-switching controlling the diffusion and mixture process has begun to attract attention. In this report, we have studied experimentally the effect of the orifice configuration on the impingement heat transfer using non-circular orifices. In addition, “axis-switching phenomenon” was showed clearly by the flow visualization using the hydrogen bubble method. Orifice configurations are the regular polygons with 3 to 6 sides. Heat transfer experiments covered the distance between the orifice-to-target plate is 4 to 8 and Reynolds number is 5 × 104 and the constant heat flux is 600 W/m2. The flow was visualized in Reynolds number 1,500. In the free jet from the regular polygon orifice, when the number of sides on the orifice increased, the occurring location of "axis-switching phenomenon moved towards the orifice exit and the tendency of the iso-Nusselt number profile became the concentric profile upstream. With the decrease in the number of sides on the orifice, the iso-Nusselt number profile after “axis-switching phenomenon” was kept at the downstream.