Mixing and Agitation 93851 10
10
MIXING AND AGITATION gitation is a means whereby mixing of phases can be accomplished and by which mass and heat transfer can be enhanced between phases or with external surfaces. In its most general sense, the process of mixing is concerned with all combinations of phases of which the most frequently occurring ones are
A
7. gases with gases.
2. gases into liquids: dispersion.
3. gases with granular solids: fluidization, pneumatic conveying, drying.
4. liquids into gases: spraying and atomization.
5. liquids with liquids: dissolution, emulsification, dispersion
6. liquids with granular solids: suspension.
7. pastes with each other and with solids.
8. solids with solids: mixing of powders.
lnteraction of gases, liquids, and solids also may take place, as in hydrogenation of liquids in the presence of a slurried solid catalyst where the gas must be dispersed as bubbles and the solid particles must be kept in suspension.
Three of the processes involving liquids, numbers 2, 5,
10.1. A BASIC STIRRED TANK DESIGN
The dimensions of the liquid content of a vessel and the dimensions and arrangement of impellers, baffles and other internals are factors that influence the amount of energy required for achieving a needed amount of agitation or quality of mixing. The internal arrangements depend on the objectives of the operation: whether it is to maintain homogeneity of a reacting mixture or to keep a solid suspended or a gas dispersed or to enhance heat or mass transfer. A basic range of design factors, however, can be defined to cover the majority of cases, for example as in Figure 10.1.
THE VESSEL
A dished bottom requires less power than a flat one. When a single impeller is to be used, a liquid level equal to the diameter is optimum, with the impeller located at the center for an all-liquid system. Economic and manufacturing considerations, however, often dictate higher ratios of depth to diameter.
and 6, employ the same kind of equipment; namely, tanks in
which
MIXING AND AGITATION gitation is a means whereby mixing of phases can be accomplished and by which mass and heat transfer can be enhanced between phases or with external surfaces. In its most general sense, the process of mixing is concerned with all combinations of phases of which the most frequently occurring ones are
A
7. gases with gases.
2. gases into liquids: dispersion.
3. gases with granular solids: fluidization, pneumatic conveying, drying.
4. liquids into gases: spraying and atomization.
5. liquids with liquids: dissolution, emulsification, dispersion
6. liquids with granular solids: suspension.
7. pastes with each other and with solids.
8. solids with solids: mixing of powders.
lnteraction of gases, liquids, and solids also may take place, as in hydrogenation of liquids in the presence of a slurried solid catalyst where the gas must be dispersed as bubbles and the solid particles must be kept in suspension.
Three of the processes involving liquids, numbers 2, 5,
10.1. A BASIC STIRRED TANK DESIGN
The dimensions of the liquid content of a vessel and the dimensions and arrangement of impellers, baffles and other internals are factors that influence the amount of energy required for achieving a needed amount of agitation or quality of mixing. The internal arrangements depend on the objectives of the operation: whether it is to maintain homogeneity of a reacting mixture or to keep a solid suspended or a gas dispersed or to enhance heat or mass transfer. A basic range of design factors, however, can be defined to cover the majority of cases, for example as in Figure 10.1.
THE VESSEL
A dished bottom requires less power than a flat one. When a single impeller is to be used, a liquid level equal to the diameter is optimum, with the impeller located at the center for an all-liquid system. Economic and manufacturing considerations, however, often dictate higher ratios of depth to diameter.
and 6, employ the same kind of equipment; namely, tanks in
which
References: 1. R.S. Brodkey (Ed.), Turbulence in Mixing Operations, Academic, New York, 1975. Chopey and T.G. Hicks Eds.), McGraw-Hill, New York, 1984. 4. S . Harnby, M.F. Edwards, and A.W. Nienow, Miring in the Process Industries, Buttenvorths, Stoneham, MA, 1985. 5. A.J. Kieser, Handbuch der chemisch-technischen Apparate, SpringerVerlag, Berlin, 1934-1939. 6. W.J. Mead, Encyclopedia of Chemical Process Equipment, Reinhold, New York, 1964. 7. S. Nagata, Mixing Principles and Applications, Wiley, New York, 1975. 8. J.Y. Oldshue, Fluid Miring Technology, McGraw-Hill, New York, 1983. 9. E.R. Riegel, Chemical Process Machinery, Reinhold, New York, 1953. 10. Z. Sterbacek and P. Tausk, Miring in the Chemical Industry, Pergamon, New York, 1965. 11. J.J. Ulbrecht and G.K. Patterson, Mixing of Liquids by Mechanical Agitation, Gordon & Breach, New York, 1985. 12. V. Uhl and J.B. Gray (Eds.), Miring Theory and Practice, Academic, New York, 1966, 1967, 2 vols. W. Ullmann’s Encyclopedia of Chemical Technology, Verlag Chemie, Weinheim, Germany, 1972, Vol