【作者】 李慧清；

【导师】 乔启宇；

【作者基本信息】 北京林业大学 ， 机械设计及理论， 2000， 博士

【摘要】 压缩空气泡沫系统(CAFS)是近年来出现并得到长足发展的一种高效泡沫灭火系统。本论文首先讨论了试验用CAFS系统的设计和建立,包括CAFS系统动力配置的设计、总体参数的确定、泵和压缩机的选型及系统各部分的选型和设计。 对CAFS系统产生灭火泡沫的性能进行测定,试验结果表明泡沫的粘性、稳定性、渗透性和抗烧性能都大大优于水。泡沫表面张力系数比水降低43%～64%,粘性系数是水的20倍以上,抗烧时间是水的9～18倍。另外,泡沫的析液时间、抗烧时间与泡沫气体百分比和泡沫平均直径等因素有关。 泡沫的性能参数除与泡沫灭火剂的组分有关外,还与压缩空气和混合液的混合参数有关。分别对气液混合的方式、混合面积、混合压力等三个参数进行讨论。找到三个影响因素对泡沫质量的影响规律。 研究泡沫这种特殊流体的流变学性能时,用专门设计的钟摆式屈服应力测定装置测量泡沫的屈服应力,摆片为矩形。在极低的剪切速率下,摆杆与铅垂方向的夹角有力证明了有关泡沫屈服应力的假设。屈服应力的值可以很容易地通过摆杆与铅垂方向的夹角计算,夹角在刻度盘上可以准确地读出。泡沫屈服应力与气体百分比、析液时间、泡沫平均尺寸有关。试验得到了屈服应力与其每一影响因素的关系曲线和回归方程。由于泡沫屈服应力的几个影响因素之间不独立,有关泡沫屈服应力的机理和影响因素还有不确定之处,因此,在现有实验条件下,无法建立理想的屈服应力与其影响因素关系的数学模型。 试验还证明了泡沫的另外一个重要性质,即泡沫具有剪切变稀的性质。使旋转粘度计不同直径的三个转子分别在四种转速下转动,试验结果表现出同样的趋势,即随着剪切速率的增大,泡沫的粘性系数降低。依据粘性系数曲线和屈服应力测定结果,分别得到了泡沫剪切应力-剪切速率的曲线和公式模型。这个模型描述了泡沫这种特殊流体的流变学性质,在国内外有关的研究中未见报道。这一模型的提出对CAFS系统产生泡沫应用于森林火灾扑救有重要指导意义,可用于预测外力作用下灭火泡沫的流动行为,充分发挥泡沫的阻火和灭火效能。 另外,论文还对建立森林火灾扑救用CAFS系统提出了建议。更多还原

【Abstract】 The paper describes a newly developed high performance compressed air foam system (CAFS). The construction of the experimental CAFS includes design of the power train, selection of pump and air compressor and other parts of the system.The experimental results indicate the superior viscous, durable, wetting and fire resistant properties generated by CAFS against fire. The data of foam surface tension display an obvious decrease by 43-64% compared with pure water. The viscosity coefficient of foam is more than twenty times larger than water. As well as the fire resistant time is larger than water by 9 to 18 times. The durable time and fire resistant time of foam is dependent with gas fraction and bubble diameter etc.Apart from the ingredient of foam concentrate, mixing factors are critical to foam characters. The mixing way of compressed air and foam solution, mixing area as well as mixing pressure was found to be the key elements, which influence foam quality.In order to study the rheology of fire-fighting foam, which is similar to some special fluid, a specially designed pendulum system with rectangular bob is used to measure yield stress. The equilibrium angle away from vertical under very low shear rate strongly prove the existence of the hypothesis of the yield stress of fire foam which has been related to solid object. The yield stress can be easily calculated with the equilibrium angle precisely measured by a protractor. Some curves and equations were obtained to demonstrate the change of the yield stress as gas fraction, drainage time, bubble size increased. Disperse of some data implies the lack of independence of the factors, there is still some uncertainty about the mechanism of fire foam yield stress. It’s impossible to provide a perfect mathematical model of yield stress of foam with the equipment that we have.Another important property, which is the decline of the viscosity as the shear rate increased, is also proved to be existed based on strong support. Three rotators with different diameters under four rotate velocities show the same tendency. A valuable mathematical model is constructed to describe the rheology performance 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 suppression both in fire direct attack and acting as a firebreak.Some recommendations are also presented to construct CAFS used in forest fire suppression.更多还原