Fundamental study on washing characteristics of a novel multi-phase flow system

When a small quantity of water (of volume typically one-tenth of the dense bed total volume) is added to a gas-fluidized bed of relatively large non-wettable particles, such as 6 mm polystyrene spheres, the added water can cause a dramatic improvement in the quality of fluidization. By reducing the water requirement, the resulting fluidized bed is advantageous for washing of farm products or fragile industrial devices. In this article, the characteristics of washing in this unique multi-phase flow system are investigated. Three kinds of experiments were conducted on target cylinders immersed in a water-assisted fluidized bed to measure particle collision forces on the cylinder surface, to determine attrition of a cylinder surface and to test whitening of a cylinder covered with soiled cloth. It is shown that the washing results from a combination of gentle abrasive washing due to liquid movement and direct attrition and fragment removal caused by particle collisions with the surface.