Coalescence heterogeneous

The works of Fukuma et al. [23], Morooka et al. [24] and Clark [25] has indicated that the presence of solid particles in the reactor favours the transition to the heterogeneous flow regime. A critical solid hold-up exists, beyond which the coalescence of bubbles is more frequent. This critical value is higher with smaller particles. Clark [25], studied operation at pressure above 100 bar, and inferred that... 

Fig. 14 A/SjC>eq vs. /s>eq for PEO, PTFiF, PMA and PVAc up to es>max for all four polymers, with the symbols identical to those in Fig. 13 (A). The same plots for PMMA and PtBMA are shown in (B), where the open symbols stand for 17 < 2 mN nr1 and the filled symbols for n > 2 mN nr1. The solid and dashed curves are the same as in Fig. 4, and the surface pressure increases counterclockwise, starting from 77 = 0, Limit I, in Fig. 4. PMMA shows a discontinuous change with can be explained by the coalescence of PMMA patches existing as a heterogeneous film prior to the monolayer state. Error bars, not shown for clarity, are 0.5% and 5% for/s>eq and A/SjC>eq, respectively...

Oil and water do not mix, but on addition of a suitable surfaetant a microemulsion can be formed depending on the relative concentrations of the three components. Microemulsions (i.e. surfactant/water/oil mixtures) can also be used as reaction media see references [859-862] for reviews. Microemulsions are isotropic and optically clear, thermodynamically stable, macroscopically homogeneous, but microscopically heterogeneous dispersions of oil-in-water (O/W) or water-in-oil (W/O), where oil is usually a hydrocarbon. The name microemulsion, introduced by Schulman et al. in 1959 [863], derives from the fact that oil droplets in O/W systems or water droplets in W/O systems are very small (ca. 10... 100 nm nanodroplets). Unlike conventional emulsions, microemulsion domains fluctuate in size and shape with spontaneous coalescence and breakup. The oil/water interface is covered with surfactant molecules and this area can amount to as much as 10 m per litre ( ) of microemulsion. 

A heterogeneous pore structure with varying aspect ratio would increase the frequency of breakup and coalescence, which should increase the observed mobile ganglia size distribution. However, the basic flow mechanism should remain unchanged. Also the relative importance of snap-off as a breakup mechanism would be increased relative to dynamic splitting. Here too a detailed study seems desirable. 

---