Characteristic capillary diameter to evaluate capillary pressure of ordered particle structures based on simulation of two-phase flow

Particle wettability is an important property to design the manufacturing process and evaluate the product performance in powder and pharmaceutical technologies. The liquid penetration method is commonly used to evaluate the particle wettability. However, because the capillary pressure appearing in the particle bed is calculated with the characteristic capillary diameter based on the fluid motion through the particle bed, the method overestimates the contact angle. In this study, we simulated the liquid penetration into ordered particle layer, demonstrating that the characteristic diameters based on the fluid motion cannot estimate the capillary pressure correctly. Furthermore, we proposed two new characteristic diameters which were defined for the narrowest flow channel in the powder layer. The proposed diameters reasonably agreed with simulation results, indicating that the proposed characteristic capillary diameters can reasonably estimate capillary pressure.