Research On The Performance Of Planetary Mixer With Self-excited Metric Rotation For Sewage Treatment

As a kind of high-efficiency mixing and stirring equipment,submersible mixers play an important role in wastewater treatment.Therefore,the scientific and reasonable use of submersible mixers to improve their mixing efficiency is an important task in the design of the wastewater treatment process.Aiming at the current problems of low efficiency and high energy consumption of wastewater treatment mixing equipment in China,a self-excited metric rotating planetary mixer is designed,and a systematic study of the planetary mixer is carried out using a research method combining numerical simulation and physical tests.The main research contents include the following four aspects:(1)The traditional submersible mixer is usually fixed at a certain position in the mixing pool during operation,and the impact of the flow field formed is limited to a fixed conical area due to the rotation of the fixed-pointing impeller,which has a limited impact.In order to improve the mixing effect of the existing submersible mixer,a new type of submersible mixer is being designed: the planetary mixer with self-excited rotation,which is based on the traditional fixed submersible mixer with the function of self-excited rotation.The so-called selfexcited rotation refers to the use of the reaction force formed by the mixer’s own pushing flow to push itself around a central axis so that the effective mixing field is larger.This makes the effective mixing flow field range larger.Compared with the fixed-position submersible mixer,the planetary mixer can achieve a better mixing effect.(2)Using Fluent numerical simulation software,the flow field distribution in the stirred pool was simulated for three types of self-excited rotating planetary mixers with different horizontal clamping angles and for the fixed-position mixer,respectively.Using the UDF module of Fluent numerical simulation software,the effective mixing volumes of the fixed position mixer and the self-excited rotating planetary mixer were calculated as a percentage of the overall flow field volume,respectively.Through the velocity cloud analysis and "effective stirring domain" calculation results comparison,it was found that the horizontal angle of 30 °for the planetary mixer stirring effect is the best.Its effective mixing area is the largest,occupying 66.23% of the calculated flow field volume.The planetary mixer with a horizontal angle of 45° and 60°,respectively,is the next best.And the effective mixing area of the planetary mixer in all three cases is larger than that of the fixed-position mixer.(3)At present,the mixing effect of the submersible mixer is mainly assessed according to the effective axial propulsion distance and the effective disturbance radius of the water body cross-section specified in the CJ/T 109-2007 submersible mixer standard.However,the jet formed by the planetary mixer has radial motion in addition to the tangential motion caused by the rotation,and the jet flow and energy transmitted along the same direction are smaller compared to the fixed-position submersible mixer jet,making the length of the axial effective mixing area shorter.Therefore,the axial effective propulsion distance and the effective disturbance radius of the water section specified in the existing industry standards are not suitable for assessing the mixing performance of planetary mixers.To this end,a new experimental method is proposed to evaluate the performance of submersible mixers by determining the "mixing uniformity".This method allows one to study the distribution of uniformity in each area of the pool and to evaluate the mixing effect of the planetary mixer in a scientific way.(4)The mixing uniformity of the self-excited rotating planetary mixer and the fixedposition mixer under different trajectories and different working conditions were measured by model experiments and engineering case experiments,respectively,and the conclusion that the mixing performance of the planetary mixer is better than that of the fixed-position mixer was drawn through data comparison.In addition,a 480-hour continuous operation experiment was conducted on the engineering prototype of the planetary mixer to verify the feasibility of the self-excited rotating planetary mixer in practical engineering applications.