Mathematical modeling of combustion of micron-sized and nanometer boron particles in air with allowance for changes in the heat and mass transfer mechanism and a decreasing particle size is carried out. The Knudsen number is taken as an indicator of a transition from one state to another: a continuous medium assumption is valid for describing the heat and mass transfer mechanisms in the case where Kn $$<$$ 0.01, the free molecular regime takes place for Kn $$>$$ 10, and a transient state occurs for 0.01 $$<$$ Kn $$<$$ 10. Particle sizes at which different heat and mass transfer regimes occur with respect to boron combustion in air at pressures of 0.1–4 MPa are estimated. The time it takes for boron particles to combust within the framework of the assumption of a continuous medium and in a free molecular mode is determined. It is shown that calculation models for determining the burning time of boron particles with initial sizes close to micron-sized and nanodispersed ones should take into account a change in the heat and mass transfer mechanism with variation in the current particle radius during burnout.

中文翻译：

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粒径对空气中硼燃烧的影响

进行了空气中微米级和纳米级硼粒子燃烧的数学建模，考虑到传热和传质机制的变化以及减小的粒子尺寸。Knudsen 数被视为从一种状态过渡到另一种状态的指标：连续介质假设适用于描述当 Kn $<$$ 0.01 的情况下的传热和传质机制，自由分子状态发生在Kn $$>$$ 10，瞬态发生 0.01 $$<$$ Kn $$<$$ 10。在 0.1 压力下，硼在空气中燃烧时发生不同传热和传质机制的颗粒尺寸–4 MPa 估计。硼粒子在假设连续介质的框架内以自由分子模式燃烧所需的时间是确定的。