There are at least two main requirements for repeatable and reliable measurements of flammability and explosibility parameters of dusts: a uniform dispersion of solid particles inside the test vessel, and a homogeneous degree of turbulence. In several literature works, it has been shown that, in the standard 20 L sphere, the dust injection system generates a non-uniform dust cloud, while high gradients characterize the turbulent flow field. In this work, the dust dispersion inside the 20 L sphere was simulated for nicotinic acid/anthraquinone mixtures (with different pure dust ratios, while keeping the total dust concentration constant) with a validated three-dimensional CFD model. Numerical results show that the fields of dust concentration, flow velocity and turbulence are strongly affected by both diameter and density of the pure dusts. These different dust properties lead to segregation phenomena with the formation of zones richer in one component and leaner in the other one and vice versa, and also result in preferential paths for the solid particles inside the sphere. Overall, the obtained results highlight the need for developing a dust injection system able to overcome the shortcomings of the actual one even when testing dust mixtures.

可重复和可靠地测量粉尘的可燃性和爆炸性参数至少有两个主要要求：测试容器内部固体颗粒的均匀分散和湍流的均匀度。在几篇文献著作中，已经表明，在标准的20 L球体中，灰尘喷射系统会产生不均匀的灰尘云，而高梯度则代表了湍流场。在这项工作中，使用经过验证的三维CFD模型，模拟了烟酸/蒽醌混合物（具有不同的纯粉尘比，同时保持总粉尘浓度恒定）在20 L球体内的粉尘扩散。数值结果表明，粉尘浓度，流速和湍流场均受纯尘直径和密度的强烈影响。反之亦然，并且还为球体内的固体粒子提供了优先路径。总的来说，所获得的结果突出表明，需要开发一种即使在测试粉尘混合物时也能够克服实际的缺点的粉尘喷射系统。