Abstract This paper focuses on investigating the dynamic behaviour of foam flows, including flow regimes, their transitions and pressure profiles in relation to foam characteristics (foam holdup and wetness) at different surfactant concentrations (0–500 ppm). The experiments cover a wide range of gas and water flowrates in a 4.3 m long vertical acrylic pipe with 44 mm internal diameter. Flow regimes and their underlying mechanisms are characterised through Power Spectral Density analysis of the associated pressure fluctuation signals, collected at 100 Hz frequency. A flow map is developed for foam flow in a vertical pipe based on the gas and liquid Webber numbers, representing different flow regimes. The results from this study reveal that, even at small concentrations, the surfactant attenuates flow fluctuations, as observed in the pressure data, resulting a relatively uniform flow compared with air-water flows. The results also indicate the promoting effect of surfactant on the flow transition from churn to annular flow at much lower gas velocities compared to air-water flows. The flow transition from slug to churn and churn to annular in foam flows is shown to be associated with an increase in foam wetness. The lowering effect of surfactant on the pressure gradient is most pronounced at lower gas rates. Increasing the gas rate in the foam flow encourages bubble breakup, leading to the formation of a denser foam, composed of smaller bubbles carrying more liquid in the lamella of the foam network. This therefore leads to a higher pressure gradient at higher gas rates.

中文翻译：

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垂直管道中空气-水流与泡沫流的流动动力学比较

摘要 本文重点研究泡沫流动的动态行为，包括在不同表面活性剂浓度（0-500 ppm）下与泡沫特性（泡沫滞留率和湿度）相关的流动状态、它们的转变和压力分布。实验涵盖了内径为 44 mm 的 4.3 m 长垂直丙烯酸管道中的各种气体和水流量。通过在 100 Hz 频率下收集的相关压力波动信号的功率谱密度分析来表征流态及其潜在机制。基于气体和液体韦伯数为垂直管道中的泡沫流动开发了流程图，代表了不同的流动状态。这项研究的结果表明，即使在低浓度下，表面活性剂也会减弱流量波动，如压力数据中所观察到的那样，与空气-水流相比，产生相对均匀的流动。结果还表明，与空气-水流相比，表面活性剂在低得多的气体速度下对从搅动流向环形流的流动转变有促进作用。泡沫流中从段塞到搅动和搅动到环形的流动转变显示与泡沫湿度的增加有关。表面活性剂对压力梯度的降低作用在较低的气体速率下最为显着。增加泡沫流中的气体速率会促进气泡破裂，从而形成更致密的泡沫，由在泡沫网络的薄片中携带更多液体的较小气泡组成。因此，这导致在更高的气体速率下更高的压力梯度。结果还表明，与空气-水流相比，表面活性剂在低得多的气体速度下对从搅动流向环形流的流动转变有促进作用。泡沫流中从段塞到搅动和搅动到环形的流动转变显示与泡沫湿度的增加有关。表面活性剂对压力梯度的降低作用在较低的气体速率下最为显着。增加泡沫流中的气体速率会促进气泡破裂，从而形成更致密的泡沫，由在泡沫网络的薄片中携带更多液体的较小气泡组成。因此，这导致在更高的气体速率下更高的压力梯度。结果还表明，与空气-水流相比，表面活性剂在低得多的气体速度下对从搅动流向环形流的流动转变有促进作用。泡沫流中从段塞到搅动和搅动到环形的流动转变显示与泡沫湿度的增加有关。表面活性剂对压力梯度的降低作用在较低的气体速率下最为显着。增加泡沫流中的气体速率会促进气泡破裂，从而形成更致密的泡沫，由在泡沫网络的薄片中携带更多液体的较小气泡组成。因此，这导致在更高的气体速率下更高的压力梯度。泡沫流中从段塞到搅动和搅动到环形的流动转变显示与泡沫湿度的增加有关。表面活性剂对压力梯度的降低作用在较低的气体速率下最为显着。增加泡沫流中的气体速率会促进气泡破裂，从而形成更致密的泡沫，由在泡沫网络的薄片中携带更多液体的较小气泡组成。因此，这导致在更高的气体速率下更高的压力梯度。泡沫流中从段塞到搅动和搅动到环形的流动转变显示与泡沫湿度的增加有关。表面活性剂对压力梯度的降低作用在较低的气体速率下最为显着。增加泡沫流中的气体速率会促进气泡破裂，从而形成更致密的泡沫，由在泡沫网络的薄片中携带更多液体的较小气泡组成。因此，这导致在更高的气体速率下更高的压力梯度。