单液滴撞击受热枫桦木炭化表面的实验研究

Drop impact onto charring surface of heated Betula costata wood

通过模拟实验研究了水滴及含4%氟表面活性剂(AFFF)液滴分别撞击室温和加热枫桦木炭化表面的碰撞动态过程。实验中加热枫桦木表面温度为124.7℃,纯水滴初始直径为(2.4±0.1)mm,含4%AFFF液滴初始直径为(1.8±0.1)mm,液滴滴落高度为15～40cm。采用Photron Fastcam高速摄影仪记录液滴碰撞的动态过程,拍摄帧数为2000fps。研究结果表明:水滴撞击枫桦木炭化表面后飞溅液滴数、最大铺展因子都随着水滴撞击速度的增大而增大。纯水滴撞击加热枫桦木炭化表面4ms后迅速飞溅形成次生液滴,小液滴滚动蒸发聚合成一个大液柱,大液柱起伏多次后形成一个小液柱停留在枫桦木表面。而含4%AFFF液滴撞击受热枫桦木炭化表面时,液滴碰撞后与木材发生良好浸润现象。

An experiment was carried out to study the process of pure water drop and water drop with 4% surfactant AFFF impacting on wood surfaces heated or at room temperature.The temperature of the heated wood surface was 124.7℃,while the height of the drop was varied from 15 cm to 40 cm.The initial diameters of pure water drop and the water drop with 4% AFFF were fixed at（2.4±0.1）mm and（1.8±0.1）mm,respectively.The impacting processes were recorded by using a Photron Fastcam high-speed digital camera with 2000 fps.The experimental results show that the number of splashed droplets and the maximum spread factor increase as the impacting velocity of drop increases.When the pure water drop impacts on the heated charring wood surface,it will splash many daughter drops after 4 ms and produce a big liquid column on the surface.A few milliseconds later,the water drop changes to a small liquid column and stays on the wood surface.However,the well wetting process occurs with the water drop containing 4% AFFF.