单凹坑壁面的瞬态红外传热测量与流场显示

Transient infrared heat transfer measurements and surface flow visualization on a single dimpled wall

关键词:  凹坑  涡流  换热系数  红外热像仪  瞬态测量

Key words:  Dimple  Vortex  Heat transfer coefficient  Infrared thermography  Transient measurement

摘要:

为了揭示凹坑冷却结构的强化传热机理,基于第三类边界条件下的一维半无限大瞬态导热模型,用红外热成像仪的瞬态测温技术和金属网快速加热技术,对矩形通道内壁面进行了瞬态传热测量,获得了光滑壁面和带有单个球面凹坑壁面的局部对流换热系数分布,并用油-粉末法对凹坑壁面进行了壁面流场显示,实验雷诺数范围1.58×104~6.36×104。实验发现凹坑强化换热与其诱导形成的涡流结构密切相关,单个球面凹坑引起的涡流可以使凹坑下游边缘附近的局部换热最大增强80%左右,凹坑下游尾迹区域的平均换热增强20%~30%。

Abstract:

To reveal the mechanism of heat transfer enhancement with dimpled wall,local heat transfer coefficient distributions on a wall with a single spheric dimple were experimentally investigated in a rectangular channel.The heat transfer rate on a smooth wall was also measured for comparison.A transient heat transfer method was used by assuming a one-dimensional semi-infinite conduction model during the experiment.Step rising of the mainstream temperature was accomplished by using a fast-response metallic-net heater,and the transient temperature distributions on the test surface were measured with an infrared thermography.Surface flow visualization on the dimpled wall was made using oil and powder.Reynolds numbers ranges from 1.58×104 to 6.36×104.It was observed that the heat transfer rate on a dimpled wall has a close relationship to the vortex structure created by dimple.Vortex induced by a single spheric dimple can increase the heat transfer rate for a maximum of 80% at the downstream edge of the dimple.Averaged level of 20%～30% heat transfer enhancement was achieved in the area of dimple wake.