Simulation of gass-solid particle flow in the acceleration zone of a pneumatic conveyor

Abstract

A computational simulation study of gas-solid particle flow in acceleration region of a vertical pipe has been carried out to examine pipe wall deposition of powders in a vertical pneumatic conveyor being a part of detergent production process. CFD (Computation Fluid Dynamics) technique in 2-D cylindrical coordinate is employed to compute two phase turbulent "Two-fluid" (Eulerian) model by using the CFD software "Phoenics V.2.1". In the first part of this study, the model validation is performed by simulating the flow conditions of Tsuji et al. [1984] using various two phase turbulent models. Computed gas and particle axial velocity profiles together with gas phase turbulent intensity profiles at 70 * diameter of various turbulence models, namely, standard k-sigma model (Harlow-Nakayama [1968]), model of Chen-Wood [1986] and model of Mostafa-Mongia [1988] are compared with experimental data obtained by Tsuji et al. [1984]. Obviously, Standard k-sigmamodel (Harlow-Nakayama [1986]) is found to be better than Chen-Wood' model [1986] and Mostafa-Mongia' model [1988] in predicting experimental data of Tsuji et al. [1984]. The modification of particle velocity profile computation is traeated by including particle shear stress term in particle momentum equation. Particle shear stress term inclusively incorporated with standard k-sigma turbulence model computations yield better numerical results over those computed by particle shear stress term exclusive model. In the second part of this study, the validated model is applied to simulate airlift conveyor flow in acceleration zone. Airlift conveyor flow in three different inlet configurations, namely, uniform inlet configuration which air-powder mixture uniformly enters in entire pipe inlet area, mixture-annulus inlet configuration which air-powder mixture enters in annulus area of pipe and air only enters in core area of the pipe, mixture-core inlet configuration which air-powder mixture enters in core area of the pipe and air only enters in annulus area of the pipe are simulated in order to study and evaluate powder concentration in near-wall region and powder-wall collision rate. Simulation of the mixture-core inlet configuration case yields the most favorable results in view of reduction of powder concentration in near-wall region and powder-wall collision rate. This configuration is further studied by varying mixture-core inlet area. The simulation results show that powder concentration in near-wall region and powder-wall collision rate decrease as mixture-core inlet area decreases.