Effect of screw design on hopper drawdown of spherical particles in a horizontal screw feeder
Effect of screw design on hopper drawdown of spherical particles in a horizontal screw feeder
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DOI：
10.1016/j.ces.2011.07.043
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发表时间：
2011-11
影响因子：
4.7
通讯作者：
Justino Fernández;P. Cleary;W. Mcbride
中科院分区：
文献类型：
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作者：
Justino Fernández;P. Cleary;W. Mcbride
螺旋给料机用于以受控的速度从料斗和料仓中取出材料。料仓内流动的均匀性取决于下降模式，而下降模式又取决于螺杆和料斗的设计、颗粒形状和壁摩擦效应。一个关键的设计要求是确保沿着料斗开口的整个长度实现螺杆容积的逐渐增加，从而产生均匀的压降。如果没有实现这一点，则可能会导致输出流中的成分变化和其他操作问题（例如结块）。迄今为止的螺杆设计通常基于分析模型，有时无法实现预测的流动模式。在本研究中，离散元法 (DEM) 用于预测一系列传统螺杆设计（包括可变螺杆螺距、可变螺杆螺纹外径和可变芯直径）的水平螺杆进料器系统中的颗粒传输。研究了螺杆选择对颗粒质量流量、颗粒从料斗下降的均匀性、功耗、螺杆磨损和壁摩擦变化的影响。 DEM 捕获的重要特征并未被分析模型考虑在内，并且在竞争的螺杆设计之间存在很大差异，包括料斗中的颗粒循环、螺杆外部槽中颗粒床的剪切以及沿料斗的空间变化的颗粒力，这会导致不均匀的压降以及大的停滞或缓慢移动区域的存在。螺杆设计和随后的流动模式也会强烈影响功率消耗（变化高达三倍）以及螺杆磨损（其分布和大小变化很大）。最后，螺杆的表面摩擦特性被证明会强烈影响螺杆内和沿螺杆的床压实速率，导致质量流量、压降和功率消耗的均匀性发生强烈变化。
Screw feeders are used to remove material from hoppers and bins at a controlled rate. The evenness of the flow in the bin depends on the drawdown pattern, which in turn depends on the screw and hopper design, shape of the particles and wall friction effects. A key design requirement is to ensure that a progressive increase in the screws volumetric capacity is achieved along the entire length of the hopper's opening so as to produce even drawdown. If this is not achieved then compositional variations in the outgoing stream and other operational problems (such as caking) can be created. Screw designs to date have been generally based on analytical models and at times the predicted flow pattern is not achieved. In this study, the Discrete Element Method (DEM) is used to predict particle transport in a horizontal screw feeder system for a range of conventional screw designs including a variable screw pitch, variable screw flight outside diameters and variable core diameters. The influence of screw choice on the particle mass flow rate, the evenness of particle drawdown from the hopper, power consumption, screw wear and wall friction variations are all investigated. Important features captured by DEM that are not accounted for by the analytic model and which vary strongly between competing screw designs, include the particle circulation in the hopper, shearing of the particle bed in the trough just outside the screw and the spatially varying particle force along the hopper which leads to non-uniform drawdown and to the existence of large stagnant or slow moving zones. The screw design and consequent flow patterns also strongly affect the power draw with variations up to a factor of three and screw wear with large changes in their distribution and magnitude. Finally, the surface frictional properties of the screw are shown to strongly influence the rate of bed compaction within and along the screw leading to strong variation in mass flow rate, uniformity of drawdown and power draw.