小型热虹吸管脉动流动传热特性的可视化实验研究

Visualization experimental study on thermal performances of oscillation state in miniaturized two-phase thermosyphons

采用高速显微成像系统对小型热虹吸管中气液两相流型演化进行了可视化实验研究,并对其脉动流动传热特性进行了分析讨论.研究结果表明,在两端压差和重力的耦合作用下,液塞的随机形成和沿槽道方向的脉动是脉动流动的典型特征.塞状流和环状流是小型热虹吸管脉动情况下的主要流型,液塞的脉动速度约为-1.5~1.5 m/s.对于脉动流工况,在启动过程中管壁导热和气液两相的膜态蒸发、膜态冷凝是小型热虹吸管的主要传热方式,该过程中热虹吸管的壁面温度持续升高,未出现温度波动;脉动启动后,小型热虹吸管内出现了液塞的随机形成和脉动运动交替冲刷壁面现象,此过程中小型热虹吸管主要靠对流蒸发、冷凝实现热量传递,且各段壁面温度皆表现出脉动特性.

The gas-liquid two-phase flowevolutions in a miniaturized two-phase thermosyphon were experimentally investigated by a high-speed microscopic visualization system. And the performances of oscillation flowand heat transfer in a miniaturized two-phase thermosyphon were analyzed. The results indicate that,the random formation and the oscillation of the liquid plugs are the typical features of the oscillation state under the coupling effects of the pressure difference and the gravity. The plug flowand the annular floware the typical flowpatterns of the miniaturized two-phase thermosyphon in oscillation state,and the oscillation velocity of the liquid plug is from-1. 5 to 1. 5 m/s.The heat transfer regimes are the film evaporation and the condensation combined with thermal conduction of the wall in the oscillation state at start-up stage of the miniaturized two-phase thermosyphon,in which the wall temperature rises continuously without fluctuation. After the start-up stage,accompanied with the random formation and oscillation of the liquid plugs,the temperature oscillations are observed at the wall temperatures of evaporator,adiabatic and condenser sections,and the heat transfer regime is the forced evaporation and the condensation in oscillation state.