Abstract

Humidity can affect the bulk behavior of fine hygroscopic powders at multiple levels and fewer mitigation approaches are presently available to counter its adverse effects. This work reports these approaches while investigating humidity influenced frictional behavior in fine cohesive starch powder flow under confined conditions. Interparticle friction and wall friction were examined under varying relative humidity (RH) using shear and wall friction tests in the quasi-static regime. The measured stress details from the bulk powder testing in the powder rheometer revealed increased stick-slip friction in the form of unsteady stresses at lower RH which gradually decreased with increase in RH. The surface texturing of particles and modifying contact stiffness through the dry coating alleviated the nonmonotonic powder flow at all the RH conditions. The stress oscillations and the consequent increase in measured friction were attributed to the discretely distributed surface moisture causing alternate sticking and slipping of the contacts. The lubricating effect of moisture at higher RH and the surface modification facilitated steady sliding, also accompanied by reduced coefficient of friction and wall friction angle. Furthermore, the different fluid film lubrication regimes were identified and highlighted the importance of fluid-particle interactions leading to undesirable bulk behavior in fine powders.

摘要

湿度会在多个层面影响细吸湿性粉末的整体行为，目前可用于应对其不利影响的缓解方法较少。这项工作报告了这些方法，同时研究了在受限条件下细粘性淀粉粉末流动中湿度影响的摩擦行为。在准静态状态下使用剪切和壁面摩擦试验在不同的相对湿度 (RH) 下检查颗粒间摩擦和壁面摩擦。在粉末流变仪中从散装粉末测试中测得的应力细节表明，在较低 RH 下以不稳定应力形式增加的粘滑摩擦随着 RH 的增加而逐渐减小。颗粒的表面纹理化和通过干涂层改变接触刚度减轻了所有相对湿度条件下的非单调粉末流动。应力振荡和随之而来的测量摩擦力的增加归因于离散分布的表面水分导致触点的交替粘附和滑动。较高相对湿度下水分的润滑作用和表面改性促进了稳定滑动，同时降低了摩擦系数和壁面摩擦角。此外，确定了不同的流体膜润滑机制，并强调了流体-颗粒相互作用的重要性，从而导致细粉中的不良体积行为。还伴随着摩擦系数和壁面摩擦角的降低。此外，确定了不同的流体膜润滑机制，并强调了流体-颗粒相互作用的重要性，从而导致细粉中的不良体积行为。还伴随着摩擦系数和壁面摩擦角的降低。此外，确定了不同的流体膜润滑机制，并强调了流体-颗粒相互作用的重要性，从而导致细粉中的不良体积行为。