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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Fluidization and attrition of pyroclastic granular solids
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Fluidization and attrition of pyroclastic granular solids

机译：火山碎屑颗粒固体的流态化和磨损

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Pyroclastic flows have been frequently addressed in the recent volcanological literature as far as the depositional mechanisms and the field features of the related deposits are concerned. Much less attention has been paid to phenomena that control the dynamic of pyroclastic flow motion. The peculiar feature of pyroclastic flows, hence focused, is the onset of an intense upflow of gas, whose velocity may be so large that a fluidized state may be established in the granular phase. The fluidization behaviour of granular synthetic mixtures has been studied in a broad range of conditions, mostly driven by the widespread use of fluidized beds in the process industry. However, experimental studies focused on fluidization of natural granular mixtures are lacking. The aim of this paper is the characterization of the fluidization behaviour of natural pyroclastic mixtures. In particular, mixing and segregation of granular mixtures of natural origin and fluidization-induced abrasion/fragmentation of pyroclastic particles have been investigated. A pyroclastic mixture extracted from a pumice fall deposit has been used as the starting material, as it is representative of the whole material of a plinian column immediately - before collapse and emplacement of the pyroclastic flow deposits. Experimental tests have been also performed using the granular material extracted from pyroclastic flow deposits. Incipient and complete fluidization velocities, onset of particle segregation due to size and density polydispersity of the samples, elutriation of attrition-induced fine particulates and attrition-induced changes of particle size distributions have been characterized. When comparing the segregation propensity of the pumice fall and of the pyroclastic flow starting material, it is concluded that only the former exhibits significant segregation. Results of elutriation and attrition experiments highlight the transient nature of particle attrition phenomena: generation of fines by attrition of relatively coarse granular solids is at a maximum in the early stage of fluidization and decays significantly thereafter.
机译：就有关沉积物的沉积机理和田间特征而言，最近火山学文献经常讨论火山碎屑流。人们很少关注控制火山碎屑流运动动态的现象。火山碎屑流的独特特征（因此得到了集中）是气体强烈上流的开始，气体的上流速度可能很大，以致于在颗粒相中可以形成流态。已经在广泛的条件下研究了颗粒状合成混合物的流化行为，这主要是由过程工业中流化床的广泛使用所驱动的。但是，缺乏针对天然颗粒混合物流化的实验研究。本文的目的是表征天然火山碎屑混合物的流化行为。特别地，已经研究了天然来源的粒状混合物的混合和分离以及流化诱导的火山碎屑颗粒的磨损/碎片化。从浮石降落沉积物中提取的火山碎屑混合物已用作起始材料，因为它代表了紧接在火山碎屑流沉积物塌陷和就位之前的lin柱的整个材料。还使用从火山碎屑流沉积物中提取的颗粒材料进行了实验测试。表征了起初和完全的流化速度，由于样品的尺寸和密度多分散性引起的颗粒偏析的开始，磨蚀引起的细小颗粒的淘析和磨蚀引起的粒度分布的变化。当比较浮石的下落和热碎屑流起始材料的偏析倾向时，可以得出结论，只有前者表现出明显的偏析。淘析和磨耗实验的结果突出了颗粒磨耗现象的瞬时性质：在流态化的早期，相对粗粒状固体的磨耗产生的细屑最多，而此后明显衰减。

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