水滴撞击常温与过热炭化纸面动态过程试验研究

Experimental test on the dynamic process of the water drops affecting the normal and superheated paper surfaces

为了加深对水喷雾或细水雾灭A类火灾过程中涉及的表面冷却现象的认识,从而加强消防安全灭火机理及安全工程技术科学研究,试验研究了水滴撞击正常和过热纸张表面的现象,并探讨了表面过热炭化现象对固液接触润湿性、液滴飞溅、蒸发和铺展直径的影响。选取水滴为液滴,初始水滴直径为(2.4±0.1)mm,水滴撞击速度从1.4 m/s到2.8 m/s不等。试验选用复印纸和档案纸两种纸张。结果表明:在过热炭化的档案纸表面出现了一些蒸汽气泡,即气化芯;水滴发生飞溅的临界条件受炭化特性的影响较大。此外,将试验结果与液滴撞击的流体力学特征Roisman模型预测结果进行比较,大部分数据相对吻合。

The given paper is to engage itself in an experimental study over the behavior of the water drop impact on the normal and heated-up paper surface so as to increase the understanding of the engineering safety science and the surface cooling mechanism of type A fire suppression via the water spray/mist.It has investigated the effects of the surface heated charring phenomena on the solid-liquid contact wettability,the drop splash,the evaporation and the spreading diameter,too.For the above said purpose,we have also chosen the pure water drop and the initial drop diameter fixed at(2.4±0.1)mm,to test the drop impact velocities in a variety from 1.4 m/s to 2.8 m/s.And,since there are combustible solid materials popularly used for the office stationery and library as well as the other two types of paper,i.e.,the copy paper and the archival paper,it would be necessary for us to use the high-speed camera system with the experiment facilitated with a variety of the droplet features,such as the droplet diameter and the shadowgraph imagining technique.And,then,we have also taken the heated charring copy and the archival papers.In order to study the dynamic process of the drop impact on the flammable solid surface at different temperatures,we have also used the electronic microscope to measure the paper surface changes as a result of the heated charring.The results of the above experiments show that the char-heating phenomena on the paper surfaces have indeed made huge influence on the droplet dynamic process,with some vapor bubbles appearing at the surface of the heated charring archival paper with expanse of the bubble size over time.Thus,as compared with the paper surfaces at the room temperature,there tends to appear and result in lots of drops when the initial drops tend to be affected due to the higher velocities(1.7-2.8 m/s formulated,Weber numbers 97-260).To be exact,the critical velocity of the drop splashes can also be affected by the heated charring features on the charred paper surfaces heated due to the influence of the higher temperature and decreased surface roughness,which indicate the wettability of the paper has been enhanced.In addition,the experimental results also prove to be in nice agreement with the Roisman model of the hydrodynamic features of the droplet impact,with the maximum deviation rate being within the range of 12.7%.