Flow Mechanism And Flow Regime Identification Of Airlift Pumps Working In Gas Liquid Flow

With the development of gas or oil exploration,interregional transfer of water,chemical circulating water supply,agricultural irrigation technology in China,transportation technology with a long distance and high performance showed a broad market prospect.Airlift pump,as one of transportation technologies had a big advantage compered with the traditional mechanical pump,due to the simple structure,cheap cost,high reliability of airlift pump,compared with the strict requirements of mechanical pump,such as wear-resistance,seal,cool-off and lubrication.However,the mixture flow with some update and variation of gas-liquid interfaces in airlift pumps was very complex.Moreover,the mechanics mechanism and energy exchange between gas and liquid were unclear to us,which also brought a lots of problems for the design and high performance of airlift pumps.Thus,to require the the flow mechanism and to get a high development potential,we theoretically and experimentally investigated the performance of airlift pumps.The mainly works and results were shown in follows:(1)A complete model of airlift pump under different flow regimes was proposed by combining with a series of corrections of pressure drops,void fractions,phase velocities under different flow regimes was combined with the basic momentum and continuity equations.The calculated results showed that : The new formed model had a good agreement with experimental data and had a perfect prediction accuracy for pump performance.Moreover,this model could used for a wider gas range with a better prediction accuracy,compared with the traditional models,because it could adapt all kinds of flow structures in airlift pumps.(2)The performance in rising pipe and the entrainment in suction pipe were firstly experimentally investigated,and then a new flow pattern map was established.At last,the forces,pressure drop,void fraction and efficiency were calculated based on some gas-liquid two phase theories.It was found that the flow structure in airlift pumps was so complex,which could hardly predicted by the classical flow regime map in vertical gas-liquid flow,because its entrance liquid velocity showed some strong turbulent characteristics.Compared with the flow regime in classical vertical pipe,bubble flow was never found in airlift pumps due to its weak lifting force for pumping liquid.Besides,the range of gas intake for slug flow regime became shorterbecause a Taylor bubble became more fragile under a turbulent environment.Thus,the maximal liquid flow rate usually appeared in churn flow.Moreover,a mist annular flow dominated airlift pumps in a high air discharge rather than the classical annular flow as other researchers said.It was just mist annular keeping the system remain a high superficial liquid velocity due to its thicker film and more numbers of entrained drops in gas core.(3)Images of gas-liquid flow,captured by a high speed camera,was used to analyzed the fractal characteristic and the rule of alternate flow of liquid films and bubble groups,as well as the corresponding ratio of bubble group in its flow cycle.The results showed that the alternate frequency of liquid film and bubble groups in a range of 1.6Hz-3.6Hz firstly decrease and then increase with the increasing of gas velocity.In the flow cycle,bubble groups produce a good effect on improving liquid velocity due to their fast velocities with a uniform direction.A large submergence ratio could improve pump performance due to a higher ratio of bubble groups.(4)The film thickness and interface fluctuation were analyzed by extracting the curve of liquid film interface and reconstructing its spatio-temporal evolution image.The results showed that film thickness in airlift pump,in a range of 0.16D-0.25 D decrease with the increasing of gas velocity.Huge waves existing in gas-liquid interface showed Gaussian shape and a larger amplitude with a larger liquid velocity or a smaller gas velocity.(5)The pressure signal in airlift pump was first experimentally captured by pressure sensor and then analyzed by the time-frequency analysis theory.With the help of multi-fractal theory,the pressure fluctuation was analyzed.Considering about the small energy of fluctuation caused by small bubbles in high frequency,wavelet packet was employed to decompose the pressure signal into a series of sub-signals in different frequency bands.Subsequently,recurrence plot was employed to analyzed the fluctuations of these sub-signals.The results showed that the increasing air flow rate could shorten the frequency band of pressure fluctuation.It was found that main frequency bands of slug flow,churn flow,and annular flow were in ranges of 0-40 Hz,0-16 Hz,0-12 Hz,respectively.The mixture flow showed different fluctuation characteristics in different frequency bands.Pressure fluctuated chaotically in a low frequency band(0-31.25Hz),and periodically in a high frequency band(31.25-62.5Hz)due to the micro-jet caused by the intermittent small bubbles.Based on the differencesof fluctuation energy and frequency,a neural network could be employed to identify the flow regimes in airlift pump.