A Study on Pressure Drop for Liquid-Gas Foam through Channels

通过对水-空气泡沫在圆形/矩形通道中流动时的压降进行了实验研究，以阐明泡沫的流动阻力。本研究采用了膨胀比范围宽、孔道尺寸不同的泡沫材料。结果表明，泡沫的表观粘度非常高，是泡沫液的数十倍甚至数百倍。这些高数值是由于泡沫的流动特性造成的，即速度变化只存在于管壁附近，大部分泡沫不参与剪切运动。研究还表明，管道壁上的薄液层厚度对泡沫体的表观粘度有主要影响，而薄液层对泡沫体流动起润滑作用。窄高度矩形通道的压降实验结果表明，泡沫流动可以用通道壁面液体滑层润滑的塞流来表示。滑移层的厚度估计与泡沫中气泡的层间厚度相同。现有的泡沫流动模型，即C-N模型，假设泡沫是连续流体，只要选取合适的流动参数值，就可以预测泡沫流过通道的压降。然而，对于特定的泡沫流动，很难确定这些值。其适用性仅限于规模较大的通道。对于窄高度通道内的泡沫流动，中间膨胀比为6 ~ 10的泡沫，表观粘度值有减小的趋势。这是由于运动气泡的变形使滑动层厚度增加，以及由于滑动层顶部气泡-液界面的移动。通过塞流的理论模型还表明，窄通道的表观粘度与滑层厚度有很好的相关性。该研究表明，除了泡沫的性质外，还必须考虑泡沫的速度等动力学量来预测泡沫在通道中流动的表观粘度。少

An experimental study was conducted on pressure drop of water-air foam flowing through circular/rectangular channels to clarify the flow resistance of the foam. Foams with wide rage of expansion ratio and channels with various sizes were used in this study.The results showed that apparent viscosity of the foam is very high, i.e., tens or hundreds times higher than that of the foaming liquid. These high values, were resulted from the flow characteristics of the foam that velocity change exists only in the vicinity of the pipe wall and most part of the foam do not participate in the shearing motion.It was also shown that the thickness of a thin liquid layr existing on the wall of a pipe, which lubricates the bulk foam flow, has predominant effects on apparent viscosity of the foam. The experimental results of pressure drop for rectangular channels of narrow height suggested that the foam flow can be represented by a plug flow lubricated by the liquid slip-layr on the wall of the channel. … More The thickness of the slip layr was estimated to be the same order of inter-lamella thickness of the bubbles in the foam.The existing model of foam flow, i.e., C-N model, which assumes foam to be a continuous fluid, can predict the pressure drop of foam flows through channels if the appropriate values of flow parameters are employed. However, it is difficult to determine these values for particular foam flows. Its applicability is limited to channels of relatively large size.For the foam flow in a channel of narrow height, values of the apparent viscosity has a tendency to decrease for foam of intermediate expansion ratio, i.e., from 6 to 10.This is due to the increase of the slip layr thickness by deformation of the moving bubbles and due to movement of bubble-liquid interface at the top of the slip layr. It is also shown that the apparent viscosity for a narrow channel is well correlated with the thickness of the slip layr by a theoretical model of plug flow.This study shows that, in addition to the properties of the foam, a kinetic quantity such as the velocity of the foam must be taken into account to predict the apparent viscosity of the foam flowing in a channel. Less