UNSTEADY PARTICLE-REENTRAINMENT MODEL BASED ON THE INTERNAL ADHESIVE STRENGTH DISTRIBUTION OF A FINE POWDER LAYER

A new model has been developed to explain particle-reentrainment phenomena based on the adhesive-strength distribution of particles. Surface renewal of the powder layer and the time-dependent reentrainment rate are also included in the model. Experiments on particle reentrainment from a powder layer on an inside wall were carried out by use of a rectangular channel. Air velocity was controlled continuously, and currents generated by electrification of reentrained particles were recorded. Experimental study has shown that the adhesive strength is represented by a log-normal distribution. The mass of particles reentrained at a certain constant air velocity is well explained by the surface renewal model of the powder layer. It is also found that the reentrainment phenomena consist of two types of reentrainment, one with short time delay and the other with long time delay. Each of the reentrainment fluxes is approximated by a simple exponential function. The reentrainment model gives a good estimation for the unsteady reentrainment flux as a function of time under the effect of air acceleration.