As flour, plastic dust, and other powdery particles get blown through factory ducts, they become charged through contact with each other and with duct walls. To avoid discharges that could ignite explosions, ducts are metallic and grounded. Still, particles remain an explosive threat if they reach a silo while charged. The microphysics of contact charging is an active area of research, as is the quest to understand the phenomenon as it plays out on larger scales in dust storms, volcanic plumes, and processing plants. Now Holger Grosshans of the German National Metrology Institute in Braunschweig and his collaborators have developed a contact-charging model that can cope with particles and walls made of different materials [1]. What’s more, the model is compatible with computational approaches used to analyze large-scale turbulent flows.
The model treats particles’ acquisition of electric charge from each other and their surroundings as a stochastic process—one that involves some randomness. The resulting charge distributions depend on the amount of charge transferred per impact and other nanoscale parameters that would be tedious to measure for each system. Fortunately, Grosshans and his collaborators found that if they determined all parameters for one system in a controlled experiment, they could readily adjust the parameters to suit other systems.
To test their model, the researchers coupled it to a popular fluid-dynamics solver and simulated 300,000 polymer microparticles stirred by a turbulent flow while confined between four walls. The combination reproduced the complex charging patterns observed in lab experiments—and it did so efficiently: The charging model added less than 0.01% to the simulation’s computational cost.
