建立了测量微细丝表面空气自然对流换热系数3ω法模型。利用3ω法测量了直径为10.6μm水平和垂直方向铂丝表面室温下的空气换热系数。水平和垂直铂丝产生的三次谐波比较接近,结果说明,微尺度下空气的自然对流换热以导热为主,自然对流作用可以忽略。基于3ω线法原理,引入形状因子并提出了微尺度下铂丝表面换热系数的理论计算模型。空气自然对流换热系数远大于大尺度下的值,主要原因是铂丝的面积体积比值大。
The 3ωprinciple is presented for the measurement of the natural convection heat transfer coefficient.The 3ωtechnique is used at room temperature to measure the natural convection heat transfer coefficient over the surfaces of microwires of the diameters 10.6μm at horizontal and vertical orientations.The comparison of the measured third harmonics for horizontal and vertical wires shows that the heat loss from the micro scale platinum wire to the air is dominated by heat conduction and the natural convection contribution is negligible.Based on the 3ωprinciple,an expression with a heat conduction shape factor is introduced.The natural convection heat transfer coefficient at micro scale is much larger than that at macro scale,and it may be contributed to the heat capacity of the microwire and high ratio of surface to volume.
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