颗粒振动分离的浮力计算折减修正法及数值模拟

Correction and application of buoyancy calculation for particle vibration segregation

颗粒材料在振动或流动情况下的分离行为如巴西果效应已经广为人知,为了解释这种分离行为已提出了渗透、对流、凝聚等一系列解释机制,但是尚未达成共识。本文研究颗粒上浮时所受的浮力,发现已有的大颗粒浮力计算方法无法解释大颗粒粒径改变时上浮行为不同这一典型现象。为此引入粒径比对已有的大颗粒浮力计算方法进行了修正,并证明了其合理性。此外,还研究了局部阻尼系数、振幅、颗粒密度对压强分布的影响。结果表明:所建议的修正办法能正确地计算不同粒径比下大颗粒受到的浮力;随着局部阻尼系数的增大,压强最大值增大,压强曲线下降趋势由直线变为曲线;随着颗粒密度的增大,压强最大值增大,但压强曲线下降趋势变化并不明显;随着加载振幅的增大,压强最大值与下降趋势变化均不明显。

Segregation of granular materials under vibration or flow conditions such as Brazil nut effect has been well known, and a series of mechanisms such as void-filling, convection, condensation, and buoyancy have been established to explain this segregation behavior, but no agreement has been reached. This paper attempts to explain the floating behavior of large particles in fluidized particle bed by using particle segregation buoyancy mechanism. It is found that the existing methods for calculating the buoyancy of large particles cannot explain the difference of the floating behavior when the large particle size changes. A reduction method for calculating the buoyancy of large particles based on the size ratio of large and small particles was proposed to explain the above phenomenon. In the meantime, we have studied the effects of local damping, amplitude, particle density on the pressure distribution in the particle bed. The results show that the proposed reduction method can correctly calculate the buoyancy of large particles in fluidized particle bed. With the local damping increasing, the maximum of pressure increases and the downtrend of pressure changes from line to curve. With the particle density increasing, the maximum of pressure increases but the downtrend of pressure changes slightly. With the amplitude increasing, both the maximum and downtrend of pressure changes slightly, the position of pressure begin to decrease rise.