热线外低Rayleigh数自然对流换热的机理

Mechanism of natural convection around heated microwire at low Rayleigh number

采用铂丝自测流体温度的实验方法,利用50×10-6 m2·s-1硅油对低Rayleigh数下水平与竖直热线外自然对流传热的机理进行了研究,对比实验测得的实验数据和Tsubouchi、Fand的实验数据发现,实验结果与Tsubouchi的拟合曲线吻合度较高,低Ra下水平热线外的Nu高于竖直热线,但均远高于数值模拟的预测值。为了解释该现象,进行了低振动Re下的自然对流数值模拟,发现在低于某一振动Re下,Nu将与Re无关,但此时Nu与实验测的Nu基本一致,与Tsubouchi的数据偏差也在5%以内,说明微尺度铂丝外自然对流可能存在振动的作用机理。

The mechanism of natural convection around horizontal and vertical heated microwires in silicon oil is studied by using the wire itself for temperature measurement. The comparison between present measured Nusselt numbers and those in literature shows that the present data agreed better with those of Tsubouchi than those of Fand. The horizontal microwire presents a larger Nu than the vertical one at low Rayleigh number. However, all of these experimental Nu are much larger than the numerically simulated values. In order to give a theoretical explanation on this phenomenon, heated microwire with weak vibration was used in the numerical simulations. The simulated Nu shows a perfect match with the measured data and are in agreement with the correlation of Tsubouchi with a deviation less than 5%. Therefore, an enhanced heat transfer mode due to weak wire vibration is proposed, to fill the gap between simulated and experimental results.