对火灾下气溶胶灭火剂固体微粒的空间分布特点及沉降过程进行了非稳态分析，给出了微粒粒径对其运动状态的影响特征，对固体微粒在流场中的稳定性及滞留时间进行了研究，获得了微粒到达火源表面的临界粒径表达式。结果表明，微粒沉降过程其沉降的雷诺数与粒子直径相关，且基本处于低雷诺数状态，沉降速度与微粒粒径的平方成正比。当微粒直径小于100 μm时，将在很短时间内达到相对稳定的流动状态；当微粒直径达到1 μm时，可在空间中长期滞留，并通过卷吸进入火焰区域，达到灭火的效果。

In this paper, unsteady analysis was conducted on the space distribution and depositing process of the solid particulates produced by aerosol fire suppressants under fire conditions. How the particles diameters affects their movement was demonstrated.The features of the particle diameters affecting the movement status were presented. The stability and resort time for the solid particles in the flow filed was explored. And the expression of the criterion (critical) diameter for a particle depositing to the fire source surface was obtained. The results demonstrated that: the depositing process of the solid particulates and the depositing Renault number are related to the particle diameter, and the flow is almost in the relatively steady flow status with low Renault number. The depositing velocity is proportional to the square of the particle diameter. When the particle diameter is lower than 100 μm, the flow will reach the steady flow status in very short time, and while the particle diameter reaches 1 μm, the particles can suspend in the space for a long time, and can be entrained into the flame region showing the extinguishing effect.