THE DISCHARGE OF SOLID LIQUID-MIXTURES FROM HOPPERS

Experiments have been carried out using glass ballotini and diakon spheres in water, to study the flow behaviour of solid-liquid mixtures of high solid fraction from storage vessels such as hoppers. A theoretical model has been developed to predict the discharge rates from hoppers of the solid and the liquid in the mixture. This model is modified from the theory proposed for the discharge of dry powders from hoppers which have been pressurized by a gas. The solid flow rate W was experimentally found to have a similar relationship with the pressure drop DELTA-P to that of the air-assisted flow of dry particulates, i.e. W(2) is proportional to DELTA-P. Good qualitative agreement between the experimental results and the theory has also been obtained. The introduction of a discharge coefficient C(D) in the model enabled a good correlation with the experimental results. The average value of C(D) obtained from the various experiments was found to be about 0.42. This value is disappointingly low which leads to the conclusion that some aspect of the mechanics has not been included in the model. A more practical objective of this work was to understand the factors which affect the production of a consistent homogeneous food product of high particulate content for aseptic packaging.