FLOC BREAKUP ALONG CENTERLINE OF CONTRACTILE FLOW TO ORIFICE

The breakup process of flocs on the centerline in converging flow to an orifice is observed directly by stroboscopic photographs, using flocs which are composed of a small number of visible particles. An axial symmetric test section is employed to observe the floc behavior before and after the orifice and a two-dimensional one is used to observe flocs within the orifice. It is found that flocs are broken in the velocity acceleration region before the orifice, but not within and after the orifice, and that the maximum size i(max) of the flocs which experienced the elongation rate (dV(z)/dZ) is given by the following equation: i(max) = 7.0(dV(Z)/DZ)-0.2 A model for the breakup of flocs in an elongation flow is proposed, in which the floc breakup is assumed to be attributed to the difference of the drag force on the constituent particles at different locations. It is found that the variations in the size distribution of flocs and the average floc size are successfully predicted by this model.