Flow wettability

The effect of surface contamination and the wettability between the tube wall and the fluids were also studied experimentally. It has been shown that a stable annular flow and gas slug formation with a stable thin liquid film formed between the tube wall and gas slugs, which appeared at high velocities under carefully treated, clean... 

Dhir, V. K., 1992, Some Observations from Maximum Heat Flux Data Obtained on Surfaces Having Different Degrees of Wettability, in Pool and External Flow Boiling, V. K. Dhir and A. E. Bergles, Eds., pp. 185-192, ASME, New York. (2)... 

Wettability is defined as "the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids" (145). Rock wettability can strongly affect its relative permeability to water and oil (145,172). Wettability can affect the initial distribution of fluids in a formation and their subsequent flow behavior. When rock is water-wet, water occupies most of the small flow channels and is in contact with most of the rock surfaces. The converse is true in oil-wet rock. When the rock surface does not have a strong preference for either water or oil, it is termed to be of intermediate or neutral wettability. Inadvertent alteration of rock wettability can strong alter its behavior in laboratory core floods (172). 

Changing the wettability of reservoir rock surfaces from oil-wet to water-wet, increases the permeability of the formation to oil, decreases the permeability to water, decreases mobility ratio, increases sweep efficiency, increases the flowing fraction of oil at every saturation, and increases oil recovery at the economic limit of the waterflood. 

Migration of free-phase NAPLs in the subsurface is governed by numerous properties including density, viscosity, surface tension, interfacial tension, immisci-bility, capillary pressure, wettability, saturation, residual saturation, relative permeability, solubility, and volatilization. The two most important factors that control their flow behavior are density and viscosity. 

Column (11) refers to the non-wettability test using the air-flow technique. 

The overall gain of the multiphase mixture model approach above is that the two-phase flow is still considered, but the simulations have only to solve pseudo-one-phase equations. Problems can arise if the equations are not averaged correctly. Also, the pseudo-one-phase treatment may not allow for pore-size distribution and mixed wettability effects to be considered. Furthermore, the multiphase mixture model predicts much lower saturations than those of Natarajan and Nguyen - and Weber and Newman even though the limiting current densities are comparable. However, without good experimental data on relative permeabilities and the like, one cannot say which approach is more valid. 

Despite the fact that much effort has been made to model the DMFC system, considerable work remains, particularly in support of the emerging portable designs and systems. Few have treated the dominating effects of two-phase flow. No model to date has sufficient detail to provide a microfluidic theory for portable systems including effects of channel geometry and wettability characteristics of the GDL on fluid flow in the anode or cathode. Modeling studies are needed to fully elucidate the intricate couplings of methanol, water, and heat-transport... 

Fig. 12.11 Examples of pesticide concentration vs. depth, indicating preferential flow of each pesticide in individual field plots. Symbols C continuous I intermittent P ponding S spiinkhng TG technical grade EC emulsifiable concentrate WP wettable powder U undisturbed D disturbed (Ghodrati and Jury 1990)...

Extractant leakage from the pores of the polymeric membrane in SLM is due to osmotic flow of massive quantities of water through the membrane. Membrane stability decreases with increasing osmotic pressure gradient and depends upon composition of the SLM system. A high tendency to solubilize water, low extractant/aqueous interfacial tension, and high wettability of polymeric membrane leads to less stable SLMs. The following measures have been proposed for improvement of stability ... 

---