Coalescence, dispersions

Both Vermeulen et al. (V3) and Calderbank (C3) conclude that the mean particle size is a function of impeller tip speed, whereas Rodriguez et al. (R7) find it to be a function of power input per unit volume. Jackson (J1) explains this apparent discrepancy on the basis that the System of Rodriguez et at. (R7) was more coalescing in nature than the systems studied by the others (C3, V3). In a coalescing dispersion there is frequent circulation and redispersion which requires impeller power. It is further pointed out (Jl) that, although the tip speed determines the mean particle size leaving the impeller, the particle size will also depend on the frequency of circulation which is a function of power input. 

The number of PPE particles dispersed in the SAN matrix, i.e., the potential nucleation density for foam cells, is a result of the competing mechanisms of dispersion and coalescence. Dispersion dominates only at rather small contents of the dispersed blend phase, up to the so-called percolation limit which again depends on the particular blend system. The size of the dispersed phase is controlled by the processing history and physical characteristics of the two blend phases, such as the viscosity ratio, the interfacial tension and the viscoelastic behavior. While a continuous increase in nucleation density with PPE content is found below the percolation limit, the phase size and in turn the nucleation density reduces again at elevated contents. Experimentally, it was found that the particle size of immiscible blends, d, follows the relation d --6 I Cdispersed phase and C is a material constant depending on the blend system. Subsequently, the theoretical nucleation density, N , is given by... 

Spielman, L. A., and Levenspiel, O., A Monte-Carlo treatment for reacting and coalescing dispersed phase systems. Chem. Eng. Sci. 20, 247 (1965). 

Droplet Droplet Binder formation coalescence dispersion overlap by wetting capillary penetration... 

Coalescence, dispersion, and settling are all affected by dispersed phase concentration or volume fraction, 0. Liquid-liquid systems can be categorized with respect to 4> as follows ... 

Immiscible liquid-liqnid mixing involves dispersion, snspension, and coalescence of liquid drops in a second liquid phase. Effects of mixing are complex, often poorly understood, and lack industrially usable measuring tools. Scale-np is particnlarly difficult, since coalescence dispersion and suspension are affected to different degrees by scale. For a more in-depth treatment of this subject, see Chapter 12 by Leng and Calabrese in the Handbook of Industrial Mixing [1]. 

Here, (jf n) indicates (p value on the nth particle. In the coalescence/dispersion model proposed by Curl (1%3), the state of/at f + Zif is calculated from the collision frequency co. The compositions of a pair of particles, which are selected at random (denoted by wi and W2), change as ... 

Nonuniform agitation cannot generate a monodisperse system because there is a direct relationship between the dispersion velocity and the particle average size. Optimal stirring is ensured by the coalescence/dispersion ratio. 

The coalescence/dispersion factor is responsible for dispersing or particle agglomeration. Changes in the system s qualitative and quantitative components ratio during the crosslinking reaction can lead to particle collapse (the lower polymer density, when compared with that of the monomer, generates pearls with a lower volume than that of the initial droplet). 

Spielman LA, Levenspiel O. A Monte Carlo treatment for reaction and coalescing dispersed systems. Chem Eng Sci 1965 20 247. 

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