Experimental and numerical research on high pumping performance mechanism of lobed exhauster-ejector mixer

Abstract

The lobed nozzle exhauster-ejector mixer has a lot of potential applications in industry. The experimental setup is established to explore its high pumping performance mechanism. Experimental results show that the pumping performance is dominantly dependent on the primary flowing fluid “attachment” on the inner wall of the mixer. If the primary flowing fluid attaches the inner wall of the mixer in the exit section, the pumping ratio of the entrained secondary mass flow rate to the primary mass flow rate is definitely high. In order to find the high pumping performance mechanism from flow field, the N–S equations are solved. The numerical results show that the flow field to give high or the highest pumping ratio is that there is a distinct thin layer (tear layer) of the secondary flowing fluid with less velocity on the inner wall of the mixer. The distinct thin layer much decreases the friction loss between the primary high-speed flow and the solid wall. The necessary conditions for establishing the distinct thin layer are that the cross-area ratio is not too high or too low and the expand angle of the conical mixer is slightly less than the initial diffusion angle of the primary eject flow. According to the experimental and numerical results, the conical mixer with the cross-area ratio of 2.5 and the expand angle of 14.4° gives the highest pumping ratio of 0.528. The highest pumping ratio 0.598 for cylindrical mixers is experimentally in the case of the cross-area ratio of 3.8. The reason for the highest pumping ratio difference between the conical mixer and the cylindrical mixer is that in the cylindrical mixer the primary flowing fluid properly attaches the inner wall of the mixer in the outlet section and there is a larger space with negative pressure downstream of the lobed nozzle for entraining the secondary flowing fluid.