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

为了研究水-气泡沫在圆形和矩形流道中的流动阻力，进行了水-气泡沫流动的实验研究。研究中采用了膨胀率范围较大、通道尺寸不同的泡沫塑料，结果表明，泡沫塑料的表观粘度很高，比发泡液体的表观粘度高出几十倍甚至几百倍。这些较高的数值是由于泡沫的流动特性，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，还表明管壁上存在的润滑大体积泡沫流动的薄液层厚度对泡沫的表观粘度有显著影响。窄高矩形流道的压降实验结果表明，泡沫流可以用流道壁上液体滑移层润滑的推流来表示。…现有的泡沫流动模型，即假设泡沫为连续流体的C-N模型，只要选取合适的流动参数，就可以预测流道中泡沫流动的压降。然而，很难确定特定泡沫流的这些值。对于狭长流道中的泡沫流动，对于中等膨胀比的泡沫，表观粘度有减小的趋势，即从6减小到10，这是由于运动气泡的变形增加了滑移层的厚度，以及滑移层顶部气泡-液体界面的移动所致。研究还表明，窄通道的表观粘度与滑移层厚度有很好的相关性，这一研究表明，除了泡沫的性质外，还必须考虑泡沫的速度等动量来预测通道中泡沫的表观粘度。较少

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