Numerical Simulation Of The Mixer With High Efficiency And Low Energy Consumption

With the rapid development of economy and the expanding of urbanization and industrialization, the urban sewages increase dramatically. The way of sewage treatment with low cost and high efficiency is very necessary to every city. It is well known that the mixer is a major sewage treatment equipment, whose mixing efficiency and energy consumption has an important effects on whole industry of the sewage treatment. It is extremely necessary to research and develop the mixer with high efficiency and low energy consumption. Based on these ideas, we developed a new mixer using the approach of CFD.According to the basic design theory of mixer and the knowledge of CFD, a three-dimensional solid model of mixer is established. Its diameter was of 1500mm, the width of mixing tank was of 4.8m, the length of 8.0m and the depth of 6.0m. The rotating speed of mixer is 30,40 and 50r/min respectively. The numerical simulation is implemented based on the RNG turbulent model and the VOF method. The location of the free surface of mixing tank was conducted by the geometric reconstruction scheme. The PISO scheme is applied to solve of the coupled terms of velocity and pressure. The momentum, turbulent kinetic energy and turbulent dissipation rate was discretized using the second order upwind scheme and the under-relaxation factors scheme was applied for iterative solution.The numerical simulation show that the minimum velocity of water in the mixing tank is 0.02m/s and the maximal velocity is 0.20m/s when the mixer operate with the rotating speed of 30r/min, which satisfy the mixing requirements. The velocity of water gradually increases from the free surface to the bottom and it gradually decreases from the center of mixing tank to the wall of that. Simultaneously, under the impeller driving, the flow had become intense swirl flow in the vertical direction, also, there is a intense swirl flow near the mixer region in the level direction due to the rotate of the mixer, which can achieve a perfect hydraulic conditions. The numerical calculations also illustrated that the energy consumption was 337.Ow when the rotating speed of mixer was 30r/min without taking into account the mass of impeller, shaft and the friction loss of gearbox, it was 868.1 w when that was 40r/min and it was 1679.8w when that was 50r/min, which is higher efficiency, lower energy consumption compared with the traditional mixers under the same conditions.