Flow field analysis and structure optimization of jet stirring device for jet flotation machine

In order to optimize the structure of the jet stirring device of jet flotation machine,a reasonable CFD numeri- cal simulation calculation scheme was selected to examine the two characteristics of ejecting performances and flow field characteristics comprehensively. The area ratio,the length of throat tube,the layout mode and the position of ejec- tor tube were optimized. Four different structural parameters including long throat tube,short throat tube,guide vane nozzle and non-guide vane nozzle were designed for testing. The influence of the length of throat tube and the guide vane in nozzle on ejecting capability was examined and verified. The influence of the guide vanes in the nozzle on the morphological evolution of jet stream was investigated by laser particle velocimetry. The results show that the mixing ef- ficiency of jet device is the most ideal when the area ratio (a) is at 1. 96 to 3. 24,the nozzle-to-throat distance (Le ) is at 0. 2Dh to 0. 6Dh(Dh :throat tube diameter),the ejector tube is arranged on both sides,the nozzle is equipped with guide vane and the length of throat tube is at 6Dz to 12Dz(Dz :nozzle diameter). The position of the ejector tube also has little effect on that. When the injection chamber pressure is at 0. 145 to 0. 160 MPa and the guide vanes are ar- ranged in the nozzle,the suction capacity of long and short throat tube is increased by 30. 73% and 33. 94% respec- tively. The suction capacity of long throat tube is 15% higher than short one when the ejector tube is fully opened. Structural parameters also have effect on the flow field,the center velocity of throat tube attenuates faster when the area ratio is increased and the ejector tube is arranged closer to the nozzle outlet,but the change of the nozzle-to-throat dis- tance has less effect on that. When the length of throat tube is less than 6Dz ,the jet stream core continues to the outlet of throat tube,and the momentum and mass of the ejecting and working fluid cannot be completely exchanged in throat tube. When setting guide vanes in nozzle,it can promote the reduction of the region in the center of the stream. The reason is that the stream is ejected from the nozzle in the form of a rotating jet,forming a turbulent flow field that is more conducive to exchange the momentum and mass of the working and ejecting fluid. Based on ideal ejecting per- formances and flow field characteristics,when area ratio is at 3. 24,the nozzle-to-throat distance Le is at 0. 6Dh ,the e- jector tube adopts bilateral symmetrical facing to the jet stream core area,the guide vanes set in the nozzle and the length of the throat tube is at 6Dz to 12Dz ,those are optimal structural parameters of the jet stirring device.