(40a) Flushing Phenomenon due to the Impact Force on the Powder Surface by Free Falling of Particles

A flushing is a phenomenon that the cohesive fine powder spouts out from the clearance, which is often observed in a mechanical feeder or a hopper, when the voidage of powder is large and the interstitial air pressure is increased. In the present study, we experimentally examine the onset condition of flushing by charging soft wheat flour into a bin that has an orifice at the bottom. In this case, the interstitial air pressure is increased by the impact force of free falling powder on the top surface of powder. The mean size of powder is 69.8 µm, material density is 1417 kg/m³, and moisture content is between 11.9 and 13.4 %. The orifice diameter is changed from 1 to 10 mm. We obtained the following results: (1) the flushing occurs when the mass flow rate of powder into the bin exceeds 500 g/s, the interstitial air pressure at the bottom of the bin is larger than 300 Pa, and the initial voidage is more than 0.54, (2) the interstitial air pressure at the beginning and end of flushing increases with decreasing the orifice diameter.