Experimental study of molten bubble layer growth and bubble size distribution in post‐flame‐spread PMMA samples
Experimental study of molten bubble layer growth and bubble size distribution in post‐flame‐spread PMMA samples
复制标题
火焰扩散 PMMA 样品中熔融气泡层生长和气泡尺寸分布的实验研究
作者：
S. Hossain;I. Wichman;F. Miller;S. Olson
虽然热塑性塑料作为固化材料具有许多理想的特性，但它们是易燃的，很容易燃烧。聚甲基丙烯酸甲酯(PMMA)的二次燃烧样品是本研究的重点。在火焰传播过程中，PMMA形成一个含有熔融表层的气泡，影响扩散速度和表面质量外流。这项研究考察了PMMA样品中气泡的形成和分布，该样品先前经历了火焰传播，然后重新硬化为固态。本文讨论的实验是在窄通道装置(NCA)中进行的，该装置减少了重力(浮力)对火焰传播的影响。用数字图像分析(DIA)测定气泡大小和计数。通过将样品图像等分成8个等面积截面，对烧焦样品进行了分析。比较了气泡大小(面积)的频率分布。根据气泡尺寸分布的经验概率密度函数(PDF)对分布函数进行了拟合。对数正态分布预测了所有分段的气泡尺寸分布。气泡分布函数可以用来描述聚合物材料在火焰传播过程中发生热转变的物理过程。
Although thermoplastics possess many desirable traits as solidified materials, they are combustible and burn readily. Post burning samples of polymethylmethacrylate (PMMA) are the focus of this study. During flame spread, PMMA forms a bubble containing molten surface layer that influences the spread rate and the surface mass efflux. This study examines the formation and distribution of bubbles inside a PMMA sample that has previously been subjected to flame spread and then re‐hardened into its solid state. Experiments discussed herein were conducted in a Narrow Channel Apparatus (NCA), which reduces the influences of gravitation (buoyancy) on flame spread. Bubble sizes and counts were determined using digital image analysis (DIA). The burnt samples were analyzed by dividing sample images into eight equal area sections. Frequency distributions of bubble size (area) were compared. Distribution functions were fitted against the empirical probability density function (PDF) for the bubble size distribution. The log‐normal distribution predicts the bubble size distribution for all segments. The bubble distribution function can be used to describe physical processes inside the polymeric material as it undergoes thermal transformation by the spreading flame.