Particle-segregation in chutes, silos, conveyor belts and rotating drums

溜槽、筒仓、传送带和转鼓中的颗粒分离

基本信息

批准号：
EP/M022447/1
负责人：
Nico Gray
金额：
$ 175.75万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FM022447%2F1
关键词：
Particle segregation chutes silos conveyor

项目摘要

Particles of differing size or density often segregate in industrial flows such as chutes, silos, conveyor belts and rotating drums. This is the single biggest cause of material non-uniformity, which poses significant problems in handling and processing the grains, leading to plant downtime and product wastage. The most common form of segregation occurs in surface avalanches, which develop whenever a static granular material is tipped above its angle of repose. For example, pouring one's muesli into a bowl at breakfast! These avalanches are very efficient at sorting particles by size, with the large ones rising to the surface and the small ones percolating down to the base. The density of the grains may enhance or counteract this effect. When these flows come to rest a rich variety of particle size and density distributions develop in the deposit, sometimes with large regions of just one particle type. This naturally presents a major problem in processes that are supposed to be well-mixed. Understanding the segregation process and being able to model it effectively is the first step in being able to develop strategies to mitigate its effects. This proposal aims to use a powerful combination of small scale experiments, theory, continuum simulation and discrete element simulations (where the interactions of every single particle are modeled) to determine the functional dependence of the segregation rates on particle properties, as well as the applied shear-rate and pressure. The resulting mathematical model will then be applied to more complex flows, where there is mass transport between the the surface avalanche and the static, or slowly moving, grains beneath. This presents the project with its biggest challenge, because the rheology of granular materials is still very poorly understood, compared to fluids, which makes simulating the flow in a silo problematical. Over the past decade there has however been significant progress in the development of the so called mu(I)-rheology, which works over a large range of parameter space. Our aim is to regularize the model, by including additional physics, so that it can be applied in all regions of the flow and hence solve for the bulk velocity field. This will then allow the evolving particle-size and density distribution to be computed, so that we can understand in detail how pockets of just one particle type form. With our industrial partners we develop mitigation strategies, that use our knowledge of segregation to design clever chutes and silos that greatly reduce its effects.

不同尺寸或密度的颗粒经常在工业流程中分离，例如溜槽、筒仓、传送带和转鼓。这是造成材料不均匀的最大原因，这给谷物的处理和加工带来了严重问题，导致工厂停机和产品浪费。最常见的偏析形式发生在表面雪崩中，当静态颗粒材料倾斜到其休止角以上时，就会发生雪崩。例如，早餐时将麦片倒入碗中！这些雪崩非常有效地按大小对颗粒进行分类，大颗粒上升到表面，小颗粒渗透到底部。颗粒的密度可以增强或抵消这种效应。当这些流停止时，沉积物中会形成丰富多样的颗粒尺寸和密度分布，有时大面积区域仅含有一种颗粒类型。这自然会在应该充分混合的过程中提出一个主要问题。了解隔离过程并能够对其进行有效建模是能够制定减轻其影响的策略的第一步。该提案旨在利用小规模实验、理论、连续介质模拟和离散元模拟（其中对每个颗粒的相互作用进行建模）的强大组合来确定分离率对颗粒特性的函数依赖性，以及所应用的剪切速率和压力。然后，所得的数学模型将应用于更复杂的流动，其中表面雪崩与下方静态或缓慢移动的颗粒之间存在质量传输。这给该项目带来了最大的挑战，因为与流体相比，颗粒材料的流变学仍然知之甚少，这使得模拟筒仓中的流动变得困难。然而，在过去十年中，所谓的 mu(I) 流变学的发展取得了重大进展，该流变学适用于大范围的参数空间。我们的目标是通过包含额外的物理场来规范模型，以便它可以应用于流动的所有区域，从而求解体积速度场。然后，这将允许计算不断变化的颗粒尺寸和密度分布，以便我们可以详细了解一种颗粒类型的口袋是如何形成的。我们与工业合作伙伴一起制定缓解策略，利用我们的隔离知识设计巧妙的溜槽和筒仓，大大减少其影响。