Experimental and numerical investigation on optimization of foaming performance of the kenics static mixer in compressed air foam system

The current mixers in the compressed air foam system used to generate liquid foam have high flow resistance. Kenics static mixer may be a better choice for making foam because its spiral structure can lower the flow resistance. However, the effects of the structure of Kenics static mixer on the properties of liquid foam remain unclear. The primary objective of this work is to study the influences of aspect ratio, transition angle, and the number of elements of Kenics static mixer on foaming performance and make the structural design optimization. The results indicated that the aspect ratio of the Kenics static mixer had the greatest impact on the foam properties, followed by the number of elements, and the transition angle had the smallest impact. The velocity distributions were distinct at the same relative position for different aspect ratios. When the number of elements exceeded four, the increase in the number of elements hardly changed the velocity distributions. The results also emphasized the critical role of velocity distribution in improving the coefficient of variation and elucidated a strong correlation between the coefficient of variation and foaming performance. The findings can offer guidance for the optimal design of the foam generator.