Specific mixing power

FIGURE 16.8 Graph of the predicted vs observed specific mixing power consumption. Summary of Fit... 

The specific mixing power can also be determined from (9.335) by experimentally determining the rate of a mass transfer or the heat released in the process. For instance, the dissolution of solid materials is limited by mass transfer and could be used for calculation of mass transfer coefficients and specific mixing power. An example illustrating how the calculations could be performed for a three-phase system will be presented in the following section. 

Figure 9.29. Specific mixing power as a function of double movements frequency (left) in a shaked reactor (right).

D.Yu. Murzin, V.Yu. Konyukhov, N.V. Kul kova, M.I. Temkin, Difiusion from surfaces of suspended particles and specific mixing power in shaked reactors, Kinet. Katal. 33 (1992) 728. 

The shape, size, and baffling of a specific mixing vessel significantly influences the Reynolds number, flow, and power numbers. 

There is no constant scale-up factor for each specific mixing system/process [29]. The two independent impeller variables come from speed, diameter, or power, because once the impeller type/style has been selected. 

The EV power requirements depend on the car s end use and assumed acceleration demands. For example, the specifications for safe driving in a mixed ICEV and EV urban traffic of a small compact-type EV have been defined as acceleration from 0 to 50 mph in <20 s. The specific peak-power corresponding to these demands has been calculated as 80-90 wkg for conditions of optimum use of the AC power train (i.e., for constant-power acceleration following the initial period in which the peak-power is attained at the maximum tractive effort ). The majority of near-term and advanced batteries could, at least potentially, meet these demands. 

The constant may depend on process variables such as temperature, rate of agitation or circulation, presence of impurities, and other variables. If sufficient data are available, such quantities may be separated from the constant by adding more terms ia a power-law correlation. The term is specific to the Operating equipment and generally is not transferrable from one equipment scale to another. The system-specific constants i and j are obtainable from experimental data and may be used ia scaleup, although j may vary considerably with mixing conditions. Illustration of the use of data from a commercial crystallizer to obtain the kinetic parameters i, andy is available (61). 

Between 1 s and 1 min specific contact time, conduction heat-transfer performance decreases theoretically as the 0.29 power of contact time. This is consistent with empirical data from several forms of indirect-heat dryers which show performance variation as the 0.4 power of rotational speed (21). In agitator-stirred and rotating indirect-heat dryers, specific contact time can be related to rotational speed provided that speed does not affect the physical properties of the material. To describe the mixing efficiency of various devices, the concept of a mixing parameter is employed. An ideal mixer has a parameter of 1. 

Published figures for inflation rates are based on some particular mixture of goods and sei vices that is chosen to represent the material wants of the average citizen. If a given quantity of this specific mixture cost 100 last year and now costs 120, then the mix has suffered a 20 percent rate of inflation. The purchasing power of the currency (i.e., of the 120) in respecl of these goods and sei vices has consequently fallen by a factor of ( 120 — 100)/ 120, or 16.7 percent. 

In any event, the users of the mixer can issue a mechanical specification aud determine the speed, diameter of an impeller, aud power with in-house expertise. Or they may issue a processes specification which describes the engineering purpose of the mixing operation and the vendor will supply a description of the mixer process performance as well as prepare a mechanical design. 

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