Enhanced fire-fighting performance of aqueous film-forming foam (AFFF) by tuning bubble size and expansion ratio with kenics static mixers

Fire-fighting foams are highly desirable materials for extinguishing a fire and preventing fuel re-burning in the chemical industry. Here, we developed a novel compressed-air foam system (CAFS) with the Kenics static mixer as the foam generator to make fire-fighting foams. Physical properties of commercial aqueous film-forming foam (AFFF), commercial fluorine-free foam and homemade fluorine-free foam made by CAFS were characterized by measuring the expansion ratio and bubble size. Within the Fluent framework, we analyzed the turbulence properties of the flow field during foaming by coupling the Euler model and the k-epsilon model to explain the difference in physical properties of the foam. Then, we conducted fire-extinguishing tests of AFFF made by Kenics mixers upon a standard heptane pool fire. Furthermore, the relationship between foam properties, flow characteristics in CAFS, and the fire-extinguishing performance of AFFF was explored. The fire extinguishing time of foam could be shortened by 30-40% by increasing the aspect ratio and the gas-liquid ratio of the Kenics static mixer. This work is meaningful for understanding the influence of mixer structure on foaming performance and guiding the design optimization of a highly efficient CAFS.