Power Consumption of Impellers

Power Consumption of Impellers Power consumption is related to fluid density, fluid viscosity, rotational speed, and impeller diameter by plots of power number (g P/pN Df) versus Reynolds number (DfNp/ l). Typical correlation lines for frequently used impellers operating in newtonian hquids contained in baffled cylindri-calvessels are presented in Fig. 18-17. These cui ves may be used also for operation of the respective impellers in unbaffled tanks when the Reynolds number is 300 or less. When Nr L greater than 300, however, the power consumption is lower in an unbaffled vessel than indicated in Fig. 18-17. For example, for a six-blade disk turbine with Df/D = 3 and D IWj = 5, = 1.2 when Nr = 10. This is only about... 

Figure 5-13. Power consumption of impellers. By permission, Rushton, J. H., Costich, E. W. and Everett, H. L., Chem. Engr. Prog., V. 46, No. 8 and No. 9,1950 [18].

Power Consumption of Impellers Power consumption is related to fluid density, fluid viscosity, rotational speed, and impeller diameter by plots of power number (g P/pN Df) versus Reynolds number (D Np/p). Typical correlation lines for frequently used impellers operating in newtonian liquids contained in baffled cylindrical vessels are presented in Fig. 18-17. These curves may be used also... 

Power consumption is an important mixing design parameter, dependent upon impeller diameter ( >), rotational speed (N), and fluid properties including viscosity (/ra) and density (p), and power consumption of impellers is usually provided as correlations of power number, Np, to Reynolds number, Nt. For fluids exhibiting time-independent power law viscosity functions, r = Kyn, the generalized Reynolds number in agitation can be expressed as ... 

Figure 25. Power number/Reynolds number curve for the power consumption of impellers.

Power consumption for impellers in pseudoplastic, Bingham plastic, and dilatant nonnewtonian fluids may be calculated by using the correlating lines of Fig. 18-17 if viscosity is obtained from viscosity-shear rate cuiwes as described here. For a pseudoplastic fluid, viscosity decreases as shear rate increases. A Bingham plastic is similar to a pseudoplastic fluid but requires that a minimum shear stress be exceeded for any flow to occur. For a dilatant fluid, viscosity increases as shear rate increases. 

Figure 10.11. Power consumption, (a) Ratio of power consumptions of aerated and unaerated liquids. Q is the volumetric rate of the gas (O) glycol ( X ) ethanol ( ) water. [After Calderbank, Trans. Inst. Chem. Eng. 36, 443 (1958)]. (b) Ratio of power consumptions of aerated and unaerated liquids at low values otQ/Nd3. Six-bladed disk turbine ( ) water ( ) methanol (10%) (A) ethylene glycol (8%) (A) glycerol (40%) Pg = gassed power input P = ungassed power input Q = gas flow rate IV = agitator speed d = agitator-impeller diameter. [Luong and Volesky, AIChE J. 25, 893 (1979)].

Can you determine the power consumption and impeller speed of a 1,000-gallon fermenter based on the findings of the optimum condition from a geometrically similar one-gallon vessel If you cannot, can you scale up by using a different fluid system ... 

The power consumption by impeller P in geometrically similar fermenters is a function of the diameter Dl and speed N of impeller, density p and viscosity p. of liquid, and acceleration due to gravity g. Determine appropriate dimensionless parameters that can relate the power consumption by applying dimensional analysis using the Buckingham-Pi theorem. 

Tests were run on pumps (without impellers) to determine the power consumption of the seals. These were unbalanced single seals, outside seals, and double seals, with carbon on... 

In a mixing process, changes in torque on the blades and power consumption of the impeller occur as a result of... 

It is quite possible (and, indeed, quite pertinent) to talk about the power consumption of the impeller, which is, obviously, quantitatively less than the power consumption of the motor and relates directly to the load on the impeller. 

The power consumption of the mixer motor differs from that of the impeller by the variable amount of power draw imposed by various sources (mixer condition, transmission, gears, couplings, motor condition, etc.). 

Newton (power) number, which relates the drag force acting on a unit area of the impeller and the inertial stress, represents a measure of power requirement to overcome friction in fluid flow in a sfirred reacfor. In mixer-granulation applications, this number can be calculated from the power consumption of the impeller or estimated from the power consumption of the motor. 

For accuracy, in power number Np calculations, the power of the load on the impeller rather than the mixer motor should be used. Before attempting to use dimensional analysis, one has to measure/estimate power losses for empty bowl or dry stage mixing. Unlike power consumption of the impeller (based on torque measurements), the baseline for motor power consumption does not stay constant and changes significantly with load on the impeller, mixer condition, or motor efficiency. This may present inherent difficulties in using power meters instead of torque. Torque, of course, is directly proportional to power drawn by the impeller (the power number can be determined... 

The relevance list (Table 5) included power consumption of the impeller (as a response) and six factor quantities impeller diameter, impeller speed, vessel height, specific density and dynamic viscosity of the wet mass, and the gravitational constant. 

Before adding the liquid, measure the baseline level of motor power consumption or impeller torque Tq at the dry mix stage. 

During the batch, stop the process frequently to take samples and, for each sample, note the endpoint values of power consumption or impeller torque Tg. For each of these end-points, measure the resulting wet mass density p. As a result, you will be able to obtain some data that will relate the... 

Espinosa-Solares T., Brito-De La Fuente E., Tecante A., Tanguy P.A., Power consumption of a dual turbine-helical ribbon impeller mixer in ungassed conditions, Chem. Engng. J. 67 (1997), p. 215-219... 

The power consumption of an impeller in a perfectly agitated tank of a Newtonian-type liquid can be calculated with the power number, P [11], This dimensionless number is conceived as a... 

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