Abstract:
The combustion of aluminum agglomerate particles with a diameter of 215 $\div$ 840 $\mu$m in free fall in air at atmospheric pressure was investigated. Initially, spherically symmetric combustion is replaced by asymmetric combustion, fragmentation occurs; eventually, the combustion process ends with the formation of an oxide residue. The listed events are characterized by the corresponding time. In this article, the duration of the symmetric combustion stage is determined – on average 0.5 $\pm$ 0.1 in relation to the combustion time. Empirical approximating dependences of the coordinate and velocity on time ($x(t)$ and $v(t)$) for particles of different diameters are obtained. To perform analytical calculations of the motion of burning particles, the viscosity of air in the vicinity of the particle was chosen to be 6.98 $\cdot$ 10$^{-5}$ Pa $\cdot$ s, which corresponds to an average temperature of 2,005 K. By comparing the empirical and calculated dependencies $x(t)$ and $v(t)$, the effective aerodynamic drag coefficient of the particle was determined depending on its size in the form $C_d(D, \mathrm{Re})$ = (9.33 + 0.13$D$)/$\mathrm{Re}$, where $\mathrm{Re}$ is the Reynolds number from the range 0.2 $<\mathrm{Re}<$ 5.2. For estimated calculations, $C_d$ = 77/$\mathrm{Re}$ can be taken.
Keywords:aluminum agglomerate, diameter, free-fall combustion in air, symmetric and asymmetric combustion stages, particle motion, combustion temperature, aerodynamic drag coefficient.
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