Breakage hydrodynamic

The techniques that have been used to characterise the mechanical properties of microparticles may be classified as indirect and direct. The former includes measurement of breakage in a "shear" device, for example, a stirred vessel (Poncelet and Neufeld, 1989) or bubble column (Lu et ah, 1992). However, the results from these indirect techniques are rather difficult to use since the mechanical breakage depends not only on the mechanical properties but also the hydrodynamics of the processing equipment, and the latter are still not well understood. To overcome this problem, a cone and plate viscometer that can apply well-defined shear stresses has been used to study breakage of hybridomas (Born et ah, 1992), but this is not a widely applied or applicable technique because the forces are too small to break most cells. 

It is encouraging that substantial progress has been made in analyzing the hydrodynamics of droplet interactions in dispersions from fundamental considerations. Effects of flow field, viscosity, holdup fraction, and interfacial surface tension are somewhat delineated. With appropriate models of coalescence and breakage functions coupled with the drop population balance equations, a priori prediction of dynamics and steady behavior of liquid-liquid dispersions should be possible. Presently, one universal model is not available. The droplet interaction processes (and... 

The fluid particle breakage controls the maximum bubble size and can be greatly influenced by the continuous phase hydrodynamics and interfacial interactions. Therefore, a generalized breakage mechanism can be expressed as a balance between external stresses (dominating component), o, that attempts to disrupt the bubble and the surface stress, ai/d, that resists the particle deformation. Thus, at the point of breakage, these forces must balance, o This balance leads to the prediction of a critical Weber number, above which the fluid particle is no longer stable. It is defined by [36] ... 

Ghalehchian, j. S. 2002 Prediction of the hydrodynamics of rotating disc contactors based on a new Monte-Carlo simulation method for drop breakage. Journal of Chemical... 

Consider the coalescence of drops with fiilly retarded (delayed) surfaces (which means they behave as rigid particles) in a developed turbulent flow of a lowconcentrated emulsion. We make the assumption that the size of drops is much smaller than the inner scale of turbulence R Ao), and that drops are non-deformed, and thus incapable of breakage. Under these conditions, and taking into account the hydrodynamic interaction of drops, the factor of mutual diffusion of drops is given by the expression (11.70). To determine the collision frequency of drops with radii Ri and Ri (Ri < Ri), it is necessary to solve the diffusion equation (11.36) with boundary conditions (11.39). Place the origin of a spherical system of coordinates (r, 0,0) into the center of the larger particle of radius i i. If interaction forces between drops are spherically symmetrical, Eq. (11.36) with boundary conditions (11.39) assumes the form... 

The influence of electrical fields on hydrodynamics and thus on mass transfer has been excellently reviewed by Yamaguchi [77,78]. It is thus possible to produce monodispersed droplet swarms up to extreme viscosities in the nanoscale (Figure 18.22). Here, the force balance on a nozzle leads to a dismpture of drops [79]. Under similar electrical but different geometrical conditions, breakage of an emulsion will occur, when due to polarization droplets form chains and will coalesce to bigger droplets as is technically used in secondary oil recovery, breaking down the water in oil emulsions [80]. Thus, coalescence and droplet formation in the electric field is sensitive to minor... 

Physical or mechanical methods of cell disruption are the most widely researched in terms of containment. The underlying principle is either by breakage of the cell wall by mechanical contact, the application of liquid or hydrodynamic shear forces, or the application of solid shear forces. Cell disruption by non-physical methods generally involve simple operations which may be carried out in large tanks or vessels, which may or may not require agitation. 

Yew, F. F. H. and Davidson, N., Breakage by hydrodynamic shear of the bonds between cohered ends of lambda-DNA molecules, Biopolymers 6 659 (1968). 

The final particle size distribution depends on the droplet/ particle breakage and coalescence occurring during the whole process. Droplet breakage occurs when the hydrodynamic stress exceeds the interfacial and viscoelastic energies [116]. Droplet coalescence depends on the energy dissipation rate, the physical properties of the systems (viscosity and density of the continuous phase, and interfacial tension), volume... 

---