沸腾换热强化特性实验研究

Experimental Study on Enhanced Boiling Heat Transfer

沸腾换热具有传热温差低、换热系数高等优点,对提高设备的紧凑性、经济性和安全性具有重要意义。目前,核动力装置中主要以光管作为沸腾换热元件,沸腾换热强化的空间很大。本文针对核动力装置非能动余热排出换热器沸腾换热工况,以水为工质,对光管及3种强化管的管外沸腾换热特性进行实验研究,得出了4种管型的沸腾换热强化特性,并分析了各强化管的强化机理。整体针翅管表面大量螺旋排列的三维翅片增大了换热面积、延缓了汽泡在壁面附近聚合形成大汽膜,使沸腾换热得到强化;多孔管采用机械方法在壁面加工出大量微细小孔,汽化核心数量和汽泡脱离频率均大幅提高,因此,沸腾换热强化效果显著;绕丝针翅管是一种复合强化手段,兼有整体针翅管和多孔管的优点,沸腾换热强化效果也较好。

Boiling heat transfer has many advantages such as low temperature difference of heat transfer and high heat transfer coefficient. It has great significance to improve equipment's compactness, economics and security. At present, smooth tubes are still widely used as boiling components in nuclear power plant; there is great extension to improve the boiling heat transfer coefficient. In this paper, water was used as boiling medium, and the boiling heat transfer characteristics of smooth tube and three other kinds of enhanced tubes including integral pin-fin tube, porous surface tube and winded pin-fin tube were studied experimentally. On the base of the experimental investigation, the enhanced mechanisms of the enhanced tubes were analyzed. There are large mounts of three-dimensional pin-fin on the surface of integral pin-fin tube which can significantly increase the heat transfer area and prevent bubbles coalition surrounding the tube. The porous tube is fabricated by forming numerous of micro-cavities on the surface of smooth tube, and the amount of embryo nucleus and the bubble growth frequency both greatly increase, so the boiling heat transfer enhances obviously. The winded pin-fin tube is a composite enhancement tube which has the advantage of integral pin-fin tube and porous tube and it has relatively high enhancement capability.