Effect of humidity on triboelectric charging in a vertically vibrated granular bed: Experiments and modeling

•Humidity effect is modeled for triboelectrification of insulating granular materials.•Triboelectrification is accounted by humidity dependent effective work function between the materials.•The proposed model is validated by vertical vibrated bed experiments with different mass loadings.•The proposed model is used to predict qualitatively fluidized bed behavior compared with small experimental fluidized bed.

Polyethylene particles were tribocharged in a glass container subjected to vertical vibration and the resulting charge per unit mass was measured. The experimental data in conjunction with discrete element method simulations coupled with a tribocharging model were used to deduce effective work function differences between the particles and the glass container at different humidity levels. In addition, we investigated the effect of different mass loadings on the particle charge, and found that the charge increased non-linearly when the mass loading was decreased. The proposed phenomenological model was found to capture this effect. Based on the estimated effective work function difference, it was predicted that a glass-walled fluidized bed of these particles would manifest vastly different hydrodynamics at 20% and 60% relative humidity levels. These predictions were confirmed experimentally.