崩溃侠对《Industrial Dust Explosions》的笔记(4)

崩溃侠
崩溃侠 (https://heroius.com)

在读 Industrial Dust Explosions

Industrial Dust Explosions
  • 书名: Industrial Dust Explosions
  • 作者: Symposium on Industrial Dust Explosions
  • 页数: 363
  • 出版社: Astm Intl
  • 出版年: 1987-12-1
  • 关于“有限空间”

    以往解释粉尘爆炸时,都会介绍“爆炸五边形”,即形成粉尘爆炸的5个必要条件:燃料、氧化剂、有限空间、混合、点火源。其中“有限空间”这一处,需要更明确的解释。

    Even if the volume of the system is not fixed......structural failure may still result. Explosions can occur even if the initial flammable volume is completely unconfined. ...... the degree of confinement is not entirely determined by geometric boundary constrains ...As combustion wave velocities approach the speed of sound ... expanding gas motions become too slow to provide for pressure relief, and the system becomes confined by its own dynamic state ...
    引自第6页

    文中 “confinement” 就是 “有限空间” 的实指,可译为 粉尘云爆炸发展的 “体积局限” 。

    2021-01-20 13:55:30 回应
  • 三次方定律的推导

    P9

    推导过程从 抬升压力与火焰团的体积 之间关系开始,结合 火焰速度Sb 与 基础燃烧速率Su 之间的关系,经过一定简化得到。

    三次方定律可以在容器内的层流环境应用,爆炸在管道内传播时转变为湍流后,变为符合“声学近似”(acoustic approximation):

    P12

    2021-01-26 13:09:02 回应
  • 粉尘的爆炸上限

    The KSt values reach their maxima at concentrations that correspond to the burning of near stoichiometric concentrations of volatiles ..... it is expected that a limiting rich concentration will be reached but only at extraordinarily high concentrations of several thousand grams per cubic metre (of which) the dispersion ... becomes improbable.
    引自第16页

    粉尘的爆炸,首先是在粉尘受热后,由于裂解、分解、挥发作用,在颗粒表面附近形成可燃的挥发分或蒸气,这些挥发分或蒸气发生反应。

    气体的爆炸下限是由于助燃剂的比例下降,以至于阻碍了反应的发生;而粉尘的爆炸下限不存在这个问题,在粉尘浓度增加的情况下,表面反应不会因为反应物的减少而停止,最终导致爆炸下限出现的,是粉尘负载的吸热效应(heat sink),导致火焰被扑熄(quenced)。

    2021-01-26 14:49:06 回应
  • St等级的意义

    A dust may be ascribed a dust hazard class of St number depending on its Kst value ... Kst values or St numbers can then be applied to an appropriate nomograph to determine the vent size for a specific vessel handling a given dust.
    引自第70页

    在《爆炸过程和防护措施》中,看到的泄压面积线算表,就是使用St等级作为一个检索参数。而现在由于计算方法的细致化,这个等级在定量计算中的应用几乎没有了。

    2021-02-22 17:11:34 回应