| Particle behaviour during the downwards, pneumatic injection of powder into an aqueous medium (water) has been investigated by means of a new method which involves direct measurement by making use of an Aqueous Particle Sensor (APS) unit. Through this method, phenomena and parameters related to injection processes, such as gas-particle jet penetration distance, jet diameter, jet cone angle, particle dispersion and distribution within the liquid have been investigated both qualitatively and quantitatively. Flow observations comprised part of the experimental program for the purpose of confirming the characteristics of the "gas-only" and "gas-powder" injection regimes reported by previous workers.;The effect of gas and powder flow rates (powder/gas loading ratio) in determining the injection regimes and particle behaviour within the liquid were the main parameters investigated.;It was demonstrated that the jetting regime can be easily achieved as a result of increased momentum transfer from the particles to the gas phase. However, this required a high loading of particles. Entrainment of gas with the injected particles took place not only during coupled flow (jetting) but also during decoupled (bubbling) flow, such that some gas was always entrained by the particles and penetrated the liquid as a gas-particle jet, leaving large gas bubbles at the lance tip. It was further demonstrated that the gas flow rate had a greater effect on particle suspension within the liquid than did the powder flow rate. |
