Energy dissipation drop breakup

In addition, Chandavimol et al. (1991a,b) have estimated the kinetic rate at which the bubbles go from initial size to the maximum equilibrium size as a function of energy dissipation. The rate of dispersion was found to be approximately proportional to energy dissipation rate. [See Figure 7-24 for a comparison of bubble breakup rate between vortex (HEV) and spiral (KMS type) static mixers.] In general, the equilibrium drop size is reached in a few pipe diameters. However, the drop size distribution is narrowed as the simultaneous processes of drop breakup and coalescence are continued, depending on the mixer design and fluid properties. See also Hesketh et al. (1987, 1991). 

From the above the maximum stable drop size can be estimated. There will be smaller drops, but in theory no drops larger than this. No data on distribution as yet exist for laminar breakup. Figure 7-28 compares drop size by laminar mechanisms with those calculated for turbulent flow. Smaller droplets are expected for laminar versus turbulent flow at the same energy dissipation rate. 

The value of the power density may greatly vary among sites in the apparatus. Near the tip of a stirrer, e would have a much higher value than further away. It means that the effective volume for droplet disruption is much smaller than the total volume of stirred liquid. This has two consequences. First, part of the mechanical energy is dissipated at a level where it cannot disrupt drops (and is thereby wasted). Second, droplet breakup takes a long time, because... 

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