Research On Liquid Mixing Characteristics In Swirling Jet Mixer

The liquid mixing process in swirling jet mixer was investigated by both the experiments and numerical simulation.The effects of structural parameters（including the adding position of the swirling flow and jet angle）and operating conditions of the mixer（including the jet-to-pipe velocity ratio and the Reynolds number of the mixing fluids）on the liquid mixing process were investigated.The experiments were investigated by planar laser induced fluorescence（PLIF）technique.The results show that when swirling flow is introduced into jet flow,mixing effects change obviously with increasing of jet angles under the same velocity ratio condition and there exists a optimum jet angle.In addition,the fixed jet mixer shows different mixing effect at different velocity ratio conditions,and exists a optimum velocity ratio.As the velocity ratio is greater than a certain value,the phenomena of“back splash”appears in the mixing zone for all swirling jet mixers.The position where"back splash"appears is different,which can be divided into two types:at the center of the mixing tube and the position closed to the tube wall.When the swirling flow is introduced into the cross flow,the mixing“dead zone”under the jet hole can be restrained.Comparing to the mixer without swirling flow,the distribution of concentration field is more uniform at same velocity ratio condition,and the mixing effect is obviously improved.The Reynolds number of mixing fluids has a great effect on t_90,whereas has little effect on l_90.Based on the PLIF experiments,the large eddy simulation（LES）method with dynamic kinetic energy transport model were employed to simulate the mixing process in swirling jet mixer.By analyzing the y⁺values,energy spectrum and mean mass distribution of mixer with different jet angles,it can be seen that the size of meshes meet the accuracy requirements of LES.The experimental results are in good agreement with the simulation results,and LES can accurately predict the mixing process of different mixers.The simulation results show that when swirling flow is introduced into jet flow,the location of mixing“dead zone”under jet hole changes from the position close to the tube wall to the center of the mixing tube.The velocity field becomes regular from the disordered state.When the jet angle reaches 45°,the mixing fluid will rotate down around the pipe wall,and the mixing effect turns to be worse.When the jet angle equals to 15°,the number of counter-vortex pairs in the mixing region reach to the maximum and the mixing effect is better.When the swirling flow is introduced into the cross flow,a large area of mixing“dead zone”appears in the center of the mixing tube if the angle direction of the jet flow is same to the cross flow.The shearing effect shows more weak,and the mixing effect turns to be worse.However,the shearing effect shows more intensive when the jet flow angle direction is contrary to cross flow.A lot of vortices will generated,which are conducive to the mixing process.