Three-dimensional numerical study of flow characteristic and membrane fouling evolution in an enzymatic membrane reactor

In order to enhance the understanding of membrane fouling mechanism, the hydrodynamics of granular flow in a stirred enzymatic membrane reactor was numerically investigated in the present study. A three-dimensional Euler-Euler model, coupled with k-e mixture turbulence model and drag function for interphase momentum exchange, was applied to simulate the two-phase (fluid-solid) turbulent flow. Numerical simulations of single- or two-phase turbulent flow under various stirring speed were implemented. The numerical results coincide very well with some published experimental data. Results for the distributions of velocity, shear stress and turbulent kinetic energy were provided. Our results show that the increase of stirring speed could not only enlarge the circulation loops in the reactor, but it can also increase the shear stress on the membrane surface and accelerate the mixing process of granular materials. The time evolution of volumetric function of granular materials on the membrane surface has qualitatively explained the evolution of membrane fouling.Comment: 10 panges, 8 figure

Investigation on Dynamic Meshing Process and Factors Influencing Root Crack Propagation Trajectory of a Representative Aero-engine Gear Pair

International audienceThe gear in an aero-engine experiences alternate loads therefore the stresses on gear root change significantly in meshing process. As a consequence, fatigue crack initiates on the gear root. This paper examined meshing process and crack propagation trajectory of the aero-engine gear based on explicit dynamics and linear elastic fracture mechanics. The crack on gear root affects meshing process and causes additional noise and vibration.The meshing impact and the peak of stress distribution of the gear pair is also magnified. Furthermore, the root crack propagation can cause the rim fracture and tooth fracture of gear system. The occurrence of rim fracture increases as the backup ratio (i.e., rim thickness divided by tooth height) decreases and also increases as the initial crack location is moved down the root of the tooth; the orientation of initial crack has little influence on crack propagation trajectory