THE DISCHARGE OF FINE SANDS FROM CONICAL HOPPERS

The experimental work presented in this paper has shown that the how r ates of coarse materials through conical hoppers conform to the models of Beverloo et al. (1961. Chem. Engng Sci. 15, 260) and Base and Tana ka (1959, The Engineer (London) 208, 465), with the mass flow rate bei ng proportional to D-5/2 where D is the orifice diameter. Significantl y lower dow rates were found for fine particles, though the mass flow rates were still found to be proportional to D-5/2, but with the const ant of proportionality being a function of particle diameter. This is ascribed to the presence of interstitial pressure gradients set up as the material dilates on approaching the orifice. Direct measurements o f these pressure profiles have been made, but precise numerical agreem ent with the values required to cause the reduced flow rate was not fo und. This was attributed to pressure variation across the hopper. The pressure gradients were, however, found to be independent of orifice d iameter and inversely proportional to the square of the particle diame ter. A correlation has been proposed in which the mass flow rate is pr oportional to D-5/2 multiplied by a factor which is a linear function of particle diameter squared. Of the measured flow rates 93% lie withi n +/- 20% of this correlation.