The flow behavior of the liquid/powder mixture, theory and experiment. I. The effect of the capillary force (bridging rupture)

Employing the equality of the mechanical work of shear stress and the energy of liquid bridges, a formula is developed for shear stress τ and unconfined yield strength fc of compressed powder, consisting of narrowly-sized solid particles mixed with oil. This formula predicts the dependence of shear stress and unconfined yield strength on the oil weight fraction, C, and the radius of the particles, R, as τ and fc ∝ sqrt (C)/R. Experimental data obtained with a Schulze cell were used to validate the developed formula. Experimental dependence of fc on R is in agreement with the theoretical formula. However, the experimental dependence of fc on oil weight fraction C does not agree with the theoretical predictions, especially at low C. Therefore, the theoretical model needs further modification. Despite some approximations, the theory predicts certain features, which can be useful for transport of the stressed powder/oil mixture.