Influence of the particle distribution on dust explosions in the 20 L sphere

It is essential to standardize the safety characteristics of dust explosions to mitigate their impact on the process industries. The 20 L sphere primarily investigates the safety characteristics, namely explosion pressure ($P_{\text{ex}}$) and the rate of pressure rise (${(dP/dt)}_{\text{ex}}$), of dust explosions at the laboratory level. Ensuring uniform dust distribution inside the sphere is essential for accurate data acquisition and standardization. However, whirls created by the incoming flow through the nozzle yield particles to concentrate near the wall before ignition. This study simulated the explosion inside a 20 L sphere to investigate the impact of near-wall particle concentration on the safety characteristics. The OpenFOAM model based on the Euler-Lagrangian approach was benchmarked against experimental data of lycopodium dust explosions. A novel radial homogeneity parameter $\Phi$ $(0\le \Phi \le 1)$ quantifies the near-wall particle concentration. The parameter $\Phi$ is calculated using a power law based on the radial component of particle coordinates, $\Phi =1$ indicating a uniform distribution, and $\Phi =0$ for all particles concentrating on the wall. Different particle distributions ($\Phi =0.1,0.2,\dots ,1$) are initiated before ignition. As $\Phi$ decreases from 1, $P_{\text{ex}}$ and ${(dP/dt)}_{\text{ex}}$ first decrease, but beyond a certain point, both parameters increase. At $\Phi =0.1$, both $P_{\text{ex}}$ and ${(dP/dt)}_{\text{ex}}$ reach their highest values, which are 1.75% and 10.1% higher than the uniform distribution, respectively. The lowest values arise at $\Phi =0.7$, with reductions of 0.25% and 5.6% compared to the uniform distribution. Thus, high near-wall concentrations enhance explosion intensity, while moderate concentrations result in lower intensity than the uniform distribution.