Particulate Aggregate Formation and Wall Adhesion in Microchannel Flows

A multiple-time step discrete-element approach is presented for efficient computational modeling of the transport, collision and adhesion of small particles in microchannel flows. Adhesive particulates have been identified as a leading cause of failure in many different microfluidic devices, including those currently being developed by different research groups for rapid biological and chemical contaminant sensing, fluid drag reduction, etc. As these microfluidic devices enter into the marketplace and become more extensively used in field conditions, the importance of particle adhesion and clogging will increasingly limit the reliability of such systems. At a larger scale, clogging of vehicle radiators by small adhesive particles is currently a major problem for construction vehicles operating in certain environmental conditions and certain soil types. Cooling system fouling leads to the need for frequent maintenance and machine down time. Dust fouling of equipment is also of concern for potential human occupation on dusty planets, such as Mars. The discrete-element method presented in this paper is developed to enable efficient prediction of aggregate structure and breakup, for prediction of the effect of aggregate formation on the bulk fluid flow, and for prediction of the effects of small-scale flow features (e.g., due to surface roughness or lithographic patterning) on the aggregate formation and particle deposition. We present an overview of the computational structure and modeling assumptions, including models for various forces and torques present during particle-particle collisions. We then utilize the computational method to examine the physical processes involved in aggregate formation and capture of particulate aggregates by walls in microchannel flows.