Analysis of the Granular Flowability

Granular flows are frequently encountered in the transportation of particulate materials in many industries, including pharmaceutical, chemical, mineral, metallurgical, food, cement and other industries. The problems frequently encountered in the transportation of particles include bridging, channeling, oscillating mass flow rate and other problems. The transportation of particulate materials are different from that of constitutive fluids and may be affected by the particle size and its distribution, the particles shape, the physical properties of the transporting media/piping, the inter-particle forces etc. These factors may be summarized using the term “flowability of the particles”. Currently, the well-established methods for the measurement of the flowability of the particles are still not possible. The flow characteristics of the particles are usually determined by the yield locus measured using a Jenike shear tester and thereafter a qualitative flow function is calculated. However, the Jenike measurement is complicated and is not suitable for dynamic measurements. Schrämli (1967) obtained similar Jenike yield locus for different cement powders that show obviously different flow characteristics. Although Freeman Technology (UK) and IMP Co. LTD (Japan) have show some interesting instruments for the powder flowability measurement recently, the results still lack validations. In fluidization, the particles will be fluidized when the gas drag force balances with the gravitational force, the buoyancy force and the inter-particle forces. For given fluidized particles, the inter-particle forces can be evaluated from the gas drag force and the buoyancy force. The inter-particle forces are closely related to the flowability of the particles. This project proposes a method to relate the flowability of the particles and the inter-particle forces measured in a fluidization system. A fluidized system will be used to characterize the flow properties of the particles. Research work on fluidization indicates that when the inter-particle forces are strong (i.e., particles with low flowability), the superficial gas velocity should be greater than the minimum fluidized velocity to fluidize the particles, causing overshooting. The “overshooting” is strong functions of the inter-particle forces and the loadings. This work intends to use the overshooting phenomenon to characterize the inter-particle forces and hence to estimate the flowability of the particles. The results will be comprehensively compared with Jenike flow functions and to evaluate the apparent viscosity of the particles. The pressure drop versus superficial gas velocity profile and the inter-particle interactions evaluated by pressure overshoot will be compared with theoretical Revised Ergun equation and Lifshitz theory, respectively. The particle apparent viscosity will be used to for the particulate phase in CFD simulations for granular flows.

Project ID:PB10308-2729
External Project ID:MOST103-2221-E182-068