THE FLOW OF PARTICULATE MATERIALS FROM HOPPERS Weigh belts of all kinds are very sensitive to changes in belt tension, which in turn depends to a large extent upon the power required to drag the material from the hopper. If the belt or screw is mounted horizontally under the hopper the belt fills at the back of the orifice and pulls material out under the stationary material at the front. A shear surface is set up and because the position of this is sensitive to material property its position can change. This affects the tension and hence the accuracy. Another result is to turn a mass flow hopper into a non mass flow hopper. The same problem arises with screw feeders. Possible solutions are to use a variable diameter screw or to incline the belt under the hopper so that the rate of discharge of material per unit area of the orifice is constant. The effect for a screw is shown in Fig. 10. At the present time there is no way of adequately designing such a system for a $ EGREG ATION IONAllY / r l X E D D I A N E TE R ,y,•///////////////./• INCREASING DIAHETE R Figure 10. Constant diameter screw discharge vs increasing diameter screxv discharge. cohesive material. In vie•v of these difficulties a two feeder (33) system should be considered for a high accuracy system. The first feeder conditions

70 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the material and gets it out of the hopper, the second controls the flow rate. CONCLUSIONS In this paper an attempt has been made to describe some of the work that has been done in the field of hopper ftmv from an engineering stand- point. Some of the factors that can critically affect the performance of an installation have been emphasized and should be considered before any equipment is installed. (Received: 21st January 1969) REFERENCES (1) Davis, E. W. Univ. Minn. Expt. Sta. Bull. No. 1340, No. 42 (10 May 1937). (2) Van Denburg, J. F., Bauer, W. C. Chem. Eng., Albany (28 Sept. 1964). (3) Zenz, F. A. and Othmer, D. I. Fluidization and fluid particle systems, (Rheinhold Pub- lishing Co., New York). (1960). (4) Johansen, J. R. Powder Technol., 1 328 (1968). (5) Jenike, A. W. Bulletin No. 128, Univ. of Utah, Eng. Expt. ,S'ta. (1964). (6) Walker, D. M. Chem. Eng. Sci., 21 975 (1966). (7) Lee, Y. Combustion, I10 (January 1960). (8) Richmond, O., The 'Best' profile for a gravity-type hopper. Am. Soc. Mech. Engrs. Annual Meeting (November 1962). (9) Gardner, G. C., Chem. Eng. Sci., 18 35 (1963). (10) Farley, R. and Valentin, F. H. H. Trans. Inst. Chem. Eng. London, 411 T193 (1965). (11) Jenike, A. W. Society of Mining Engineers. 268 (September 1966). (12) McDougall, J. R. and Evans, A. C. Rheol. Acta., 4 218 (1965). (13} Takahashi, M. Bull. Inst. Phys. Chem. Res. Japan, 111 984 (1933). (14) Newton, R. H., Dunham, G. S. and Simpson, T. P., Trans. Am. Inst. Chem. Eng., 41 218, (1945). (15) Franklin, F. C. and Johnson, L. N. Chem. Eng. Sci., 4, 119 (1955). (16) Jones. T. M. and Pilpel, N.J. Pharm. Pharmacol., l0 440 (1965). (17) Fowles, R. T. and Glastonbury, J. R. Chem. Eng. Sci., 10 150 (1959). (18) Rose, H. E. and Tatsuo Tanaka, Engineer, 9,08 465 (1959). (19) Zenz, F. A. tlydrocarb. Process. Petrol. Refin., 41 No. 2, 159 (1962). (20) Johanson, J. R. Trans. Soc. Min. Engrs., 9,89,, 69 (1965). (21) Hamens, A., Chem. Eng. Sci., 18 297 (1963). (22) Shinohara, K., Idemitsu, Y., Gotoh, I5. and Tanaka, T. Ind. Eng. Chem. Process Design and Development, ? 379 (1968). (23) Brown, R. L. Nature, London, 191 458 (1961). (24) Brown, R. L. and Richards, J. C. Trans. Inst. Chem. Engrs., 117 109 (1959). (25) Brown, R. L. and Richards, J. C. Trans. Inst. Chem. Engrs., 118 243 (1960). (26) Bruff, XV. and Jenike, A. V•'. Powder Technol., 1 252 (1968). (27) •Vlodarski, A. and Pfeifer, A. Paper No. 68-MH-12 presented at Am. Soc. Mech. Engrs. Materials Handling Conference, Boston, Mass. (21-23 Oct. 1968). (28) Holland, ]., Miles, J. E. P., Schofield, C. and Shook, C. A. Fluid drag effects in the discharge of particles from Hoppers. To be published in Trans. Inst. Chem. Engrs. (1969). (29) Matheson, G. L., Herbert, W. A. and Holt, P. H. Ind. Eng. Chem., 41 1101 (1949). (30) Bruff, W. Paper No. 68-MH-25 presented at Am. Soc. 3lech. Engrs. Materials Handling Conference, Boston, Mass. (21-23 October 1968).