Simulation of solid-gas two-phase flow in an impeller blower based on Mixture model

Abstract: When an impeller blower is in operation, the materials in it are conveyed mainly by means of the paddle throwing and the airflow generated by a high-speed rotating impeller blowing. In order to reveal the influence of airflow in impeller blowers on material conveying, numerical models of the air flow in the impeller blowers using the computational fluid dynamics software Fluent were developed by some scholars at home and abroad. Basic characteristics of the airflow field were obtained, which would be useful for predicting the motion of the materials. However, the studies above mentioned aimed at airflow field only, without considering materials in it, so their conclusions were not accurate.To further study the solid-gas two-phase flow mechanism in an impeller blower, a three-dimensional simulation was performed for the solid-gas two-phase turbulent flow in the impeller blower by using FLUENT software with a mixture model and a standard k-ε turbulence model. In the numerical calculation, the finite volume method was used to discretize the governing equations. The SIMPLEC algorithm was applied for the solution of the discretized governing equations. For the calculated zones composed of rotating impeller and static housing, Moving Reference Frames (MRF) was used to simulate the two-phase flows in complex geometries. Comparisons between the simulated values and the measured values of materials velocity at the discharge vertical pipe by high-speed video in reference paper 4 were made, and the reliability of the numerical simulation was verified. Meanwhile, on the basis of the analysis of the law of materials flow, contrast simulations on variations in working parameters such as paddle numbers, impeller's rotational speed, material-fed speed, and volume fraction of solid phase were carried out. It was concluded that: 1) The mixture model was successfully applied to simulate the turbulent particle-gas two-phase flows in an impeller blower, and predict the conveying property of the impeller blower. 2) Impellers with 4 paddles were more favorable for throwing/blowing materials than 3 and 5 paddles, because the materials velocity distribution of the middle plane (Z=0) of the impeller and the discharge pipe with 4-paddle was more even than that of 3-paddle and 5-paddle ones, and fewer vortex flows were generated. Besides, the axial symmetry of 4- paddle impeller blower was better than that of 3-paddle and 5-paddle ones, with a fine balance at a high speed, especially. 3) Distributions of materials velocity in the impeller blower did not change much with the impeller's rotational speed increasing, but the velocity of throwing/blowing materials changed much with it, and the higher the rotational speed was, the higher the velocity of throwing/blowing materials was. 4) An impeller's rotational speed and volume fraction of solid phase at the inlet being equal, feeding velocity determines the quantity of material fed into the impeller blower, and affects the distribution of volume fraction of solid phase at the impeller zone; In the limiting feed quantity range, higher feeding velocity means a larger volume fraction of solid phase and a higher velocity of throwing/blowing materials at the outlet, and was more favorable for conveying materials. 5) The change of the volume fraction of solid phase at inlet has less influence on the distribution of materials velocity; it only affects the volume fraction of solid phase at the entire zone, and the volume fraction of solid phase at the entire zone increases with the increase of material volume fraction at the inlet.