Interfacial instability force balance

Certain melt processing factors have to be considered in order to eliminate problems. Some of these factors can be compensated by the available plasticator and die/mold adjustments. An unsteady balance of shear forces causes the interfacial instability. Examples of the factors include ... 

The flow of the continuous phase is considered to be initiated by a balance between the interfacial particle-fluid coupling - and wall friction forces, whereas the fluid phase turbulence damps the macroscale dynamics of the bubble swarms smoothing the velocity - and volume fraction fields. Temporal instabilities induced by the fluid inertia terms create non-homogeneities in the force balances. Unfortunately, proper modeling of turbulence is still one of the main open questions in gas-liquid bubbly flows, and this flow property may significantly affect both the stresses and the bubble dispersion [141]. 

Hoburg and Melcher [7] demonstrated electrohydrody-namic instabilities in macroscale systems at an oil-oil interface with a discrete conductivity change at the interface under the influence of an applied electric field. In the presence of an applied electric field, charge accumulates at the fluid-fluid interface and the electrical force on the interface is balanced by the fluid interfacial stress tensor. At a critical field sfrength the electrical force exceeds the interfacial fluid forces and interfacial perturbations grow exponentially. Melcher determined a natural velocity scale for this instability, termed the electroviscous velocity which represents a balance between the electrical and viscous stresses at the fluid-fluid interface defined as... 

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