Analysis Of Airlift Pump Performance And Its Flow Field Structure

Airlift pump has no moving parts and its structure is very simple. So, it is very suitable for many engineering fields, such as pulp upgrade, dredging, oil and chemical liquid delivery.But,in the process of pneumatic lifting, gas-liquid-solid three phase’s interaction mechanism is complex.So,to fully grasp the three phase motion characteristics seems to be impossible,which greatly limited the performance improvement. Based on these, this paper conducted in-depth research on the lifting system’s performance and its three-phase flow field structure.The main contents are as follows:(1)A theoretical model of pneumatic lifting system was established. First, according to the momentum theorem and multiphase flow theory, a three-phase velocity model was established. Based on this, according to Newton’s second law, upgrade critical condition was derived. Then, an efficiency model was also established based on the energy conservation law. At last, these three models were all verified by experimental data. All of these models provide a foundation to analyze the system’s performance.(2)the lifting system performance was obtained. In order to obtain the optimal performance, the rules of output water and its solid quality was researched in different particle size, immersion rate,particle concentration and the intake air. The experimental and theoretical result show that: the critical gas velocity increases with the particle size but decrease withe the immersion rate; the output solid increases with the immersion rate and particle concentration,but decrease withe the particle size; Improve efficiency increases withe immersion rate,but decrease withe particle concentration and its size. What’s more, there exists an optimal intake gas which could make the output solid and the pump efficiency reach to their peaks.(3)The flow field structure in riser tube was revealed. With the help of high speed camera, the gas-liquid-solid flow pictures was captured.By these pictures, the gas and solid’s moving rules can be obtained. However, the liquid in fact is a continuous phase. Its moving rules can’t be get in the flow pictures.So,a LDV(Laser Doppler Velocimety) was used to measure the liquid velocity field. The results showed that: the flow patterns in the riser tube periodic alternate:churn flow-intensive bubble flow-spare bubble flow-churn flow,in which, the churn flow is most conducive to upgrade solid particles; In the tube, bubbles rise in spiral shape. In fact this kind of moving is a irregular spiral motion. The solids rise and fall, but their overall trend is upward motion;the liquid’s velocity distribution in tube’s cross-section trends to be a frustum-shaped.Near the tube wall, the liquid velocity gradient is very big.However, the velocity in center location becomes gently,which is also bigger than other locations.