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Natural convection heat transfer on surfaces of copper micro-wires

机译:铜微线表面上的自然对流传热

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摘要

The natural convection heat transfer characteristics and mechanism for copper micro-wires in water and air were investigated experimentally and numerically. The wires with diameters of 39.9, 65.8 and 119.1 um were placed horizontally in water inside of a sealed tube and in air of a large room, respectively. Using Joule heating, the heat transfer coefficients and Nusselt numbers of natural convection for micro-wires in ultra pure water and air were obtained. A three dimensional incompressible numerical model was used to investigate the natural convection, and the prediction with this model was in reasonable accordance with the experimental results. With the decrease of micro-wire diameter, the heat transfer coefficient of natural convection on the surface of micro-wire becomes larger, while the Nu number of natural convection decreases in water and air. Besides, the change rate of Nu number in water decreases apparently with the increase of heat flux and the decrease of wire diameter, which is larger than that in air. The thickness of boundary layer on the wall of micro-wire becomes thinner with the decrease of diameter in both water and air, but the ratio of boundary layer thickness in water to the diameter increases. However, there is almost no change of this ratio for natural convection in air. As a result, the proportion of conduction in total heat transfer of natural convection in water increases, while the convective heat transfer decreases. The velocity distribution, temperature field and the boundary layer in the natural convection were compared with those of tube with conventional dimension. It was found that the boundary layer around the micro-wire is an oval-shaped film on the surface, which was different from that around the conventional tube. This apparently reduces the convection strength in the natural convection, thus the heat transfer presents a conduction characteristic.
机译:实验和数值研究了铜微线在水和空气中的自然对流换热特性及机理。将直径分别为39.9、65.8和119.1 um的电线水平放置在密封管内的水中和大房间的空气中。利用焦耳加热,获得了超纯水和空气中微丝的自然对流换热系数和努塞尔数。利用三维不可压缩数值模型研究了自然对流,该模型的预测与实验结果基本吻合。随着微线直径的减小,微线表面上自然对流的传热系数变大,而水和空气中自然对流的Nu数减小。此外,水中的Nu的变化率随着热通量的增加和金属丝直径的减小而明显减小,这比空气中的更大。随着水和空气中直径的减小,微线壁上的边界层的厚度变薄,但是水中的边界层厚度与直径的比率增加。但是,空气中自然对流的比例几乎没有变化。结果,水中自然对流的总热传导中的传导比例增加,而对流热传导减少。将自然对流中的速度分布,温度场和边界层与常规尺寸的管子进行了比较。发现微线周围的边界层是表面上的椭圆形膜,这与常规管周围的膜不同。这显然降低了自然对流中的对流强度,因此热传递呈现出传导特性。

著录项

  • 来源
    《Heat and mass transfer》 |2014年第2期|275-284|共10页
  • 作者单位

    Energy Research Institute of Shandong Academy of Sciences, Jinan 250014, China;

    Energy Research Institute of Shandong Academy of Sciences, Jinan 250014, China;

    Energy Research Institute of Shandong Academy of Sciences, Jinan 250014, China;

    Energy Research Institute of Shandong Academy of Sciences, Jinan 250014, China;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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