摘要
压缩空气泡沫系统 (CAFS)是一种高效泡沫灭火手段。泡沫的流变学性能是森林火灾扑救中泡沫发挥直接和间接灭火能力的一个决定因素。本文用专门设计的钟摆式屈服应力测定装置测定了泡沫屈服应力 ,验证了泡沫屈服应力假设。泡沫屈服应力与泡沫气体百分比、析液时间和泡沫平均直径有关 ,试验得到了屈服应力与其影响因素的关系曲线和数学表达式模型。部分描述了泡沫这种特殊流体的流变学性质 ,对应用 CAFS系统泡沫扑救森林火灾有重要指导意义 。
The paper aims at testing the high performance of the compressed air foaming system (CAFS). As is known, aqueous foam consists of a high volume of gas fraction existing in a liquid with wetting and foaming agents generated mechanically as a result of bubble aggregation. The mixture of the agents shows a different rheology from the air and foam solution. Then a hypothesis on the yield stress or the dynamic yield stress of foam has been put forward by the author to explain the phenomenon, which displays a similar property as that of a solid. In order to further study the rheology of fire fighting foam, a specifically devised pendulum system is used with a rectangular bob to measure the yield stress of the fire foam. The equilibrium angle deviate from the vertical line under a very low shear rate strongly proves the existence of the hypothesis of the yield stress of fire foam as is related to the solid. The microstructure of bubble can partly provide the answer to the yield stress. There is an energy barrier for shear stress to overcome because the foam inclines to be airtight and spherical. Fluids with such property are usually classified as Bingham fluid. Then the curves and equations are obtained to demonstrate the change of the yield stress as gas fraction, drainage time, and average bubble size increased. A valuable mathematical model is constructed to describe the yield stress and predict the flowing behavior of fire foam occurring in open area. The origination of the model will be of great importance to the application of foam generated by CAFS in forest fire suffocation both as a direct fire fighting agent and as a fire stopping agent.
出处
《安全与环境学报》
CAS
CSCD
2002年第4期27-29,共3页
Journal of Safety and Environment
