一个四层塔中一个球的颗粒学和形态学演化预测
Prédiction de l'évolution granulométrique et morphologique d'une poudre dans un four tournant
摘要：
制造二氧化铀核燃料芯块的干法转化工艺包括两个步骤：将六氟化铀水解为氟化铀，然后在回转窑中将高温水解还原为二氧化铀。在窑尾获得的粉末的物理特性（形态、粒度分布）决定了最终性能（烧结性、流动性、生坯强度）。我们开发了一个数学模型，描述了在回转窑中的粉末的形态演变，这使我们能够预测UO2粉末的形态特征作为加工条件的函数。首先，对窑内的粉末流动进行了建模，包括密相（粉末床）和气载相（颗粒喷淋）之间的交换。该模型的一个独特之处是在计算动力学变量时考虑了升力的影响。其次，负责在形态和晶粒尺寸的变化的现象进行了识别和建模。分形团聚体的人口被认为是，其数量和尺寸的变化，由于布朗和沉降团聚，烧结，破碎，和化学反应。该模型是基于人口平衡和粒度分布划分为部分。动态和形态计算的结果进行比较，可用的测量。最后，分析了不同的形态演化机制对最终尺寸分布的影响。
英文摘要：
The dry conversion process for making UO2 nuclear fuel pellets consists of two steps: hydrolysis of UF6 to UO2F2, followed by reducing pyrohydrolysis to UO2 in a rotary kiln. The physical characteristics (morphology, particle size distribution) of the powder obtained at the kiln end determine the final properties (sinterability, flow-ability, green strength). We developed a mathematical model describing the morphological evolution of the powder in the rotary kiln, which enables us to predict morphological characteristics of UO2 powder as functions of the processing conditions. Firstly, the powder flow in the kiln was modelled, including the exchanges between a dense phase (powder bed) and an airborne phase (particles showering down). An original feature of this model is to consider the effect of lifters for calculating the dynamic variables. Secondly, the phenomena responsible for the changes in morphology and grain size were identified and modelled. A population of fractal agglomerates was considered, whose number and size change due to Brownian and sedimentation agglomeration, sintering, breaking up, and chemical reactions. The model is based on population balances and the particle size distribution is divided into sections. Results of both dynamic and morphological calculations are compared to available measurements. Lastly, the influence of the different mechanisms of morphological evolution on the final size distribution is analysed.
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