Wet Particle Adhesion Model And The Law Of The Spray Drying Sticky Wall

Wall-sticking in spray drying process must be taken into account by workers and designers. Serious wall-sticking affects productivity effect, or even results in safe accidents. The investigation of wall-sticking and the improvement of capacity of spray tower are of great significance in spray drying process and design.This paper deals with the rule of wall-sticking in spray drying process on meso-levle. The major work is as follows:(1) In order to obtain the tangential force, the Small Parameter Method is introduced to approximately analyze the stress distribution between a pair of relatively moving rigid spherical particles with an interstitial power-law fluid. The wall-sticking model can be obtained while one of the radii of the two particles is infinite.(2) The relationship between velocity and liquid bridge volume of particles and processes in spray drying process is obtained by analyzing the movement of particles and the heat and mass exchanges between particles and hot air in DC-300 type of close- cycle spray drier. Due to the direction of movement of particles, the wall-sticking model is modified into another one when particle is moving along the normal and tangential directions of the wall. By analyzing the model, the rule of wall-sticking in spray drying process is obtained:a) Particles sticking on wall reduces with improving drying extent when liquid bridge is in low saturated state;b) Drying extent has less effect on wall-sticking when liquid bridge is in high saturated state;c) Particles sticking on wall reduces with improving the surface roughness of tower wall;d) Low viscosity liquid has less effect on wall-sticking than high one.(3) Three kinds of tungsten carbide powder with different moisturecontent are produced from different feed pump pressure and hot air temperature in DC-300 type of close- cycle spray drier. The rule of wall-sticking in spray drying process is well validated by comparing the capacities of spray tower.