Flow Mechanism of Plug Conveying of Solids in a Vertical Pipe

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Plug flow is widely used in pneumatic conveying of solid particles but its mechanism is still not well understood. Particularly in a vertical pipe, the plugs of solids are easy to collapse and therefore the local concentration of solids changes largely. The concentration is the most important parameter in the plug flow analysis, because the pressure drop is determined mainly by the concentration. Since satisfactory devices of solid concentration measurement are not available except those using radio activities, it was undertaken in the first fiscal year to develop a new and safe method of measuring the solid concentration in the pipe. For that purpose, supersonic wave was used in this work. The principle of the measurement is that sonic waves are dissipate when passing through solids. Along with experiments, the rate of dissipation is calculated theoretically.In the next year, a conveying pipeline was constructed and plug flows were investigated experimentally. First, the solids flow was observed. As predicted, the plug flow showed complicated flow patterns. It is also found that signal processing speed should be improved to apply the method developed in the first year to practical pneumatic conveying.