A Study on the Unsteady Behavior of Pressurized Gas in a Channel

研究了水平管内气体突然从喷嘴喷入液体的行为。如果喷嘴直径d与管道内径D之比小于0.25，则气体在管道的上部流动。实测的锋面速度与解析值吻合较好。当h/hc<2时，表面张力σ影响波前速度，其中hc定义为hc=2[σ/（rhog）]^<1/2>。气体流动，充满管道D<hc。一个薄的液体膜残留在管壁后，通过的前端。在d/D小的情况下，膜厚度的周向分布在气体流动的上部几乎是均匀的，并且厚度取几乎恒定的值。在较低的气体流速下，表面张力和粘性力占主导地位。当气体流速很低时，气泡厚度与前缘通过后的时间有关。研究了水平通道中气泡从加热底壁沸腾的行为和壁面的烧毁。在底壁被局部加热的情况下，气泡的行为主要取决于通道的高度H。对于H>hc，气泡聚结成大气泡，并且该大气泡在通道的上部流动，保持厚度hc。对于H<hc，气体流动，充满。当H>hc和H<hc时，燃尽热流密度相差较大，当整个底壁受热时，H的不同对燃尽热流密度的影响不大。当许多组合的气泡覆盖加热壁时，燃尽与H无关。

The behavior of the gas suddenly injected from a nozzle into a liquid in a horizontal pipe is studied. If the ratio of the nozzle diameter d to the inner diameter D of the pipe is less than 0.25, the gas flows in the upper portion of the pipe. The measured front velocity agrees well with the analytical value. The surface tension sigma affects the front velocity for h/hc<2, where hc is defined by hc=2[sigma/(rhog)]^<1/2>. The gas flows, filling up the pipe for D<hc.A thin liquid film is residual on the wall after the passage of the front. In the case where d/D is small, the circumferential distribution of the film thickness is almost uniform at the upper portion where the gas flows and the thickness takes an almost constant value. At lower gas flow rate, the surface tension and the viscous force are dominant. When the gas flow rate is extremely low, the thickness is dependent on the elapsed time after the passage of the front.The behavior of the bubbles boiling from the heated bottom wall in a horizontal channel and the burnout of the wall are studied. In the case where the bottom wall is heated locally, the behavior of the bubbles is mainly dependent on the height H of the channel. For H>hc, the bubbles coalesce into a large bubble and this large bubble flows in the upper portion of the channel, keeping the thickness hc. For H<hc, the gas flows, filling up. There is much difference between the burnout heat flux for H>hc and the one for H<hc.In the case where the whole bottom wall is heated, the difference of H makes little difference in the burnout heat flux. The burnout occurs independent of H, when many combined bubbles cover the heated wall.