Deformed interface flow

Intermittent flow (or deformed interface flow), where the dispersed phase flows to a certain distance either in the form of parallel or annular flow and then produces irregular droplets (Fig. 2.Id). 

F. 2.1 Flow configurations obtained in miciochannels a Drop flow, b Plug (slug) flow, c Plug-drop flow, d Deformed interface flow, e Aimular flow, f Parallel flow, g Plug-dispersed flow, h Dispersed flow (Kashid et al. 2011)... 

Table 7.8 Mass transfer literature on slug-drop and deformed interface flow. ...

Figure 0.4 Observed flow regimes in the capillary microreactor (Y-junction ID = 1 mm, capillary ID = 1 mm), (a) Slug flow, (b) drop flow, and (c) deformed interface flow. (Adapted from Kashid, M.N. and Agar, D.W., Chem. Eng. J. 131, 1, 2007.)...

The flow patterns are combined into three regions surface tension-dominated region (slug flow), transition (slug-drop and deformed interface flow), and inertia dominated-region (annular or parallel flow). The following criteria were obtained ... 

At a given flow condition, different flow patterns were observed which can be classified into five distinct patterns depending on the interfacial configuration liquid alone (or liquid slug), gas core with a smooth thin liquid film, gas core with a smooth thick liquid film, gas core with a ring-shaped liquid film, and gas core with a deformed interface. 

Williams and Janssen (20) studied the behavior of droplets in a simple shear flow in the presence of a protein emulsifier. The effect of two structurally diverse protein emulsifiers, P-lactoglobulin and P-casein, upon the breakup behavior of a single aqueous droplet in a Couette flow field has been studied over a wide range of protein concentrations. It was found that P-casein and low concentrations of P-lactoglobulin cause the droplets to be at least as stable as expected from conventional theories based on the equilibrium interfacial tension. In such cases the presence of the emulsifier at the deforming interface is thought to enhance the interfacial elasticity. This effect can be characterized by... 

Rheology is the study of the deformation and flow of materials under the influence of an applied stress. The interfacial rheology of a surfactant film normally accounts for the interfacial viscosity and elasticity of the film. The interfacial viscosity can be classified with interfacial shear viscosity and interfacial dilational viscosity. Films are elastic if they resist deformation in the plane of the interface and if the surface tends to recover its natural shape when the deforming forces are removed. The interfacial elasticity can also be classified with interfacial shear elasticity and interfacial dilational elasticity (6, 7, 12). Malhotra and... 

The flow regimes observed in liquid-liquid flow in microchannels such as drop, slug, slug-drop, deformed interface, annular, parallel, and dispersed flow are depicted in Figure 7.9. 

In the case of an inviscid liquid (v = 0), we obtain p = +/ p as before, and the interface oscillates without damping. There is no instability because, with the liquid below the gas, both gravity and interfacial traision act to restore the deformed interface to its initial planar configuration. But with no viscous resistance to flow, the momentnm developed during the return carries the interface beyond the flat configuration to a new deformation of opposite sign to the original one. 

Here the resistance to flow is so great that the interface does not continually overshoot its equilibrium position as above (i.e., no oscillatory motion develops). Instead, the deformed interface simply returns gradually to the flat configuration. Higher viscosities produce slower damping because they reduce the velocities and velocity gradients. 

Hydrodynamic and interfacial flow In addition to the wettability, the interfacial state is determined by hydrodynamics of the system. As noted previously (12) the flow profiles in the region of an interface during its displacement are not well known. It is these flows which affect the supply and/or depletion of surfactant to the interface, as well as the flow of the interface itself. Two extreme cases can be envisaged (a) a fully flowing interface, described by Dussan (8), which results from shear forces imposed on the interface by the interaction of the the two laminar flow profiles in the two liquid phases, (b) a non-flowing interface (12). A non-flowing interface would exhibit interfacial properties dependent on the time lapse since its formation and subsequent deformations. A flowing interface would exhibit a dynamic value of interfacial tension, since fresh interface would be formed continuously. 

Interfaces exist by virtue of the adjoining bulk phases in other words, interfaces are not autonomous. The interface and the bulk phases are mechanically coupled, which implies that any deformation or flow in either adjacent bulk phase induces a motion in the interface, and vice versa. 

Adams MJ, Briscoe BJ, Kamjab M. The deformation and flow of highly concentrated dispersions. Adv in Colloid and Interface Sci 44 143, 1993. 

Simulating multiphase/multicomponent flows has always been a challenge to conventional CFD because of the moving and deformable interfaces. More fundamentally, the interfaces between two bulk phases (e. g., oil and... 

---