Power consumption 982 INDEX

Conventional stirred-tank polymeric reactors normally use turbine, propeller, blade, or anchor stirrers. Power consumption for a power-law fluid in such reactors can be expressed in a dimensionless form, Ne = Reynolds number based on the consistency coefficient for the power-law fluid. Various forms for the function f(m) in terms of the power-law index have been proposed. Unlike that for Newtonian fluid, the shear rate in the case of power-law fluid depends on the ratio dT/dt and the stirrer speed N. For anchor stirrers, the functionality g developed by Beckner and Smith (1962) is recommended. For aerated non-Newtonian fluids, the study of Hocker and Langer (1962) for turbine stirrers is recommended. For viscoelastic fluids, the works of Reher (1969) and Schummer (1970) should be useful. The mixing time for power-law fluids can also be correlated by the dimensionless relation NO = /(Reeff = Ndfpjpti ) (Tebel et aL 1986). 

POWER CONSUMPTION IN A GRINDING MILL AS A FUNCTION OF WORK INDEX... 

Power consumption or torque fluctuations are influenced by granule properties (PSD, shape index, and apparent density) and the granulation time. Fluctuation of torque/power consumption and intensity of spectrum obtained by FFT analysis can be used for end-point determination. 

The simple concept of an average mixer shear rate has been widely used in laboratory and industrial work and in most applications it has been assumed that the shear rate constant, k, is only a function of impeller type. Research is continuing on the possible influence of flow behaviour index and elastic properties, and also on procedures necessary to describe power consumption for dilatant fluids. It should be noted that in all aspects of power prediction and data analysis, power law models (equation 8.12) should only be used with caution. Apparent variability of k, may be due to inappropriate use of power law equations when calculations are made it should be ascertained that the average shear rates of interest (y = k N) lie within the range of the power law viscometric data. 

In some reports, steam drying is claimed to reduce power consumption for milling as the grindability index is increased due to steam drying. At elevated degrees of superheat and prolonged exposure times, some studies have reported a reduction in the sulfur content of coal. This is not necessarily an advantage as the sulfur will then enter the dryer-exhaust steam. Additional data are needed to evaluate this aspect in detail. 

A high MI value corresponds to a low polymer melt viscosity, and a low MI value corresponds to a high polymer melt viscosity. The term fractional melt index material refers to a polymer with a melt index less than one. These are materials with high melt viscosities, and they generally have higher power consumption and die-head pressure in extrusion as compared to polymers with higher meit index values. 

Even relatively small increases in the power law index, e.g., from 0.3 to 0.5, can reduce the critical screw speed significantly. This indicates that small increases in the power law index can cause significant increases in viscous heating and melt temperature. This is known in practice when we consider the extrusion characteristics of LLDPE relative to LDPE [325]. The power law index of LLDPE is considerably higher than that of LDPE. As a result, LLDPE tends to have more power consumption, higher melt temperatures, higher diehead pressures, and is more susceptible to melt fracture. 

If the various contributions to power consumption are carefully examined, it can be seen that a substantial portion is consumed in the clearance between the flight tip and the barrel see, for instance, Eq. 8.71(d). The power consumption in the clearance is inversely proportional to the radial clearance and directly proportional to the total flight width pw. However, the viscosity in the clearance will generally be lower than the viscosity in the channel since the polymer melt is pseudo-plastic. Figure 8.25 shows how the ratio of power consumption in the clearance to the total power consumption Z, depends on the ratio of flight width w to channel width plus flight width W + w for a polymer with a power law index n = 0.5. 

The contribution of the power consumption in the clearance rises dramatically when the power law index increases. When the fluid is Newtonian, around 80% of the total power is consumed in the clearance Thus, problems with excessive power consump-... 

Bond s Work Index A semi-empirical equation that relates the power consumption required for crushing and grinding solid particles such as rocks and ores into smaller particles. It is named after American mining engineer Fred Chester Bond (1899 1977). 

The power consumption of an extruder was measured with a standard wattmeter connected to the extruder drive unit. These results were converted into an index of specific mechanical energy (SME) consumption according to an equation formulated by Levin [2, 3] ... 

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