弹状流中连续波引起的波动频率预测模型

Prediction model of fluctuation frequencies induced by continuity waves in slug flow

【目的】弹状流是气液两相流的主要流型之一,其波动特性不仅影响多相泵的安全运行以及多相流量计测量的准确度,还会在弯头、阀门、并联管路等处引起流致振动,系统地研究弹状流的波动频率对于多相泵、多相流量计以及多相管道的安全运行具有重要意义。【方法】依据弹状流的动力学模型以及弹状流的连续波特性,采用斯托哈罗数表征弹状流的无量纲波动频率,建立了弹状流波动频率的连续波新模型,并通过调研大量文献总结了水平管道弹状流波动频率现有的经验计算模型。在表观液速为0.23~1.85 m/s、表观气速为0.88~10.0 m/s的参数范围内,使用电导探针在内径为24 mm、长为30 m的水平管中对空气-水两相弹状流的波动频率进行了实验研究,并将实验数据与所建新模型的计算结果以及不同学者提出的12个弹状流波动频率经验公式的预测结果进行对比。【结果】实验数据表明,弹状流中连续波的波动频率随表观液速的增加而增大,且有近似线性关系;当表观液速较小时,波动频率随表观气速的增加先减小后增大;当表观液速较大时,表观气速对段塞频率的影响不显著。新建模型对弹状流波动频率预测的平均相对误差约为-15%,均方根相对误差约为26%,与其他经验公式相比,平均相对误差较小、均方根相对误差为最小。【结论】现有的经验公式对弹状流波动频率的预测结果有较大的分散性,所建新模型对弹状流波动频率的预测结果与实验数据有较好的一致性。

[Objective]Slug flow is one of the main gas-liquid two-phase flow regimes.Its fluctuation characteristics not only impact the safe operation of multi-phase pumps and the measurement accuracy of multi-phase flowmeters but also arouse flow-induced vibrations in various pipeline sectors,such as elbows,valves,and places where pipelines are connected in parallel.Therefore,conducting a systematic study on fluctuation frequencies induced by slug flow is of utmost importance for securing the operation safety of these pipelines and associated fittings.[Methods]By leveraging the dynamics model of slug flow and recognizing the inherent continuity wave characteristics of slug flow,a novel continuity wave model was developed.This model employed the Strouhal number to characterize the dimensionless fluctuation frequencies induced by slug flow.Through extensive literature investigations,existing empirical calculation models for fluctuation frequencies induced by slug flow in horizontal pipelines were summarized.Additionally,an experimental study was conducted to examine fluctuation frequencies induced by air-water two-phase slug flow in a 30 m long horizontal pipeline with an inner diameter of 24 mm.Conducting probes were used to measure the fluctuation frequencies within the parameter ranges of 0.23 m/s to 1.85 m/s for superficial liquid velocity and 0.88 m/s to 10.0 m/s for superficial gas velocity.The experimental data and calculation results based on the new model were taken to compare with the prediction results obtained using 12 different empirical formulas proposed by various scholars.[Results]Analysis of the experimental data revealed that the fluctuation frequencies induced by continuity waves in slug flow increased with rising superficial liquid velocities,approximating a linear trend.At low superficial liquid velocities,the fluctuation frequency initially decreased and subsequently increased with the increase of superficial gas velocities.However,the influence of superficial gas velocities on slug frequencies became less noticeable at high superficial liquid velocities.The proposed model had an average relative error of approximately-15%,lower than the mean level observed in the empirical formulas,and the root-mean-square relative error was the lowest,approximately 26%.[Conclusion]Error analysis demonstrates that the prediction results of fluctuation frequencies induced by slug flow obtained from the proposed continuity wave model align more closely with the experimental data compared to those obtained from existing empirical formulas,exhibiting a greater degree of scattering.