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

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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.