ABSTRACT
Experience shows that moisture can drastically change the conditions of gravity flows in granular materials, and even prevent the discharge of silos (Johanson, 1975; Ranaivoson, 1988). For instance, flow measurements were made at the Ecole Centrale de Paris in conical hopper models (Biarez et al., 1989). The models were filled with slightly moist sand at different water contents. In each test, the diameter of the outlet was progressively increased until a flow was observed: Fig. 50.1 represents the minimum diameter of the outlet for which the discharge occurred versus the corre sponding water content of the sand. This experiment points out the extreme sensitivity of flow to water content, as a 1% change results in a diameter eightfold larger. Such problems happen with many kinds of products (car bon, chemicals, food products, etc.).
