Industrial bulk material transfer and handling processes often result in large dust emissions and seriously threaten workers’ health. Both dust dispersion and ventilation for dust removal are related to the entrained air flow rate under the particle flow fall process. Based on the air jet theory, this paper presents a model for unconfined and semi-confined particle flow fall processes. Theoretical formulas for the entrained air flow rate were developed, and a numerical simulation was performed to analyze the particle velocity and entrained air under unconfined and semi-confined particle flow fall processes. The results show that as the distance from the particle source to the wall’s surface decreases, the particle velocity slightly increases; however, the value of the particle velocity always varies between that of unconfined fall and fall in vacuum. It is found that when the distance of the particle source from the wall’s surface s is less than five times the width of the particle source d (s < 5d), the entrained air flow can adhere well to the wall’s surface; and when s = 0d, the entrained air flow rate caused by the semi-confined particle flow fall process is minimal and is reduced by 22% compared to that of the unconfined fall.

Graphic abstract

中文翻译：

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粒子流下降过程：对无限制和半限制坠落条件下夹带空气的系统研究

工业散装物料的转移和处理过程通常会导致大量粉尘排放，并严重威胁工人的健康。灰尘散布和除尘通风均与颗粒流下降过程中的夹带空气流速有关。基于空气喷射理论，本文提出了一种无边和半边颗粒流下降过程的模型。提出了夹带空气流速的理论公式，并进行了数值模拟，分析了无限制和半限制颗粒流下降过程中的颗粒速度和夹带空气。结果表明，随着从粒子源到墙体表面的距离的减小，粒子速度略有增加。然而，粒子速度的值总是在无限制的下降和真空下降之间变化。发现当粒子源距墙表面的距离s小于粒子源d的宽度的五倍（s  <5 d），因此夹带的气流可以很好地粘附在墙壁表面上；当s  = 0 d时，由半约束粒子流下降过程引起的夹带空气流量最小，与无边界下降相比减少了22％。

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