Drainage forced

Epstein [1988] has drawn attention to two hydrodynamic effects that he terms "neglected" and are not generally taken into account in models. They include the Magnus effect and the induced fluid drainage force. 

The fluid drainage force arises when a solid particle approaches close to a solid surface. As a particle moves to the vicinity of the surface it experiences increased viscous resistance to motion because the drag between the fluid and the two surfaces as they approach each other, gradually increases the force necessary to force the fluid from the front of the particle. The general effect of this force is to reduce deposition. 

Epstein [1988] concludes that for gases the Magnus effect and the fluid drainage force are likely to be small, but for liquids they could assume importance. The empirical sticking probability is a way of taking these unrecognised influences into account. 

The motion (steady or oscillatory) of a sphere towards a flat surface experiences a resistance to its motion. This resistance is due to the combined contribution from stokes drag on the sphere, the drainage force, and the drag force on the cantilever attached between the sphere and the force measuring apparatus, i.e., atomic force microscopy (AFM) or surface force apparatus (SFA). The exact hydrodynamic solutions of this resistance force for a sphere of radius a, approach velocity V, viscosity p, and closest separation distance h can be derived as... 

Figure 4a shows the schematic of the set up for drainage force measurement. Figure 4b shows the hydrodynamic force versus inverse separation distance for fluid of different viscosity based on... 

For electrolyte solutions and polar liquids, the amoxmt of slip depends on the electrical properties of the liquid. The sedimentation experiments report that slip is only observed for polar liquids. Drainage force experiments report slip to increase with increase in the dipolar moment of the liquid when liquids are polar. This phenomenon is attributed to the super lattice structure in liquid due to the dipole-dipole interactions. 

A uup break in the drainage curve is noticeable as the drainage force increases (increase in iVc > 0.14) this may be due to breakdown of retention forces leading to a p dular state in the liquor between particles. 

Figure 4a shows a schematic of the device for drainage force measurement. Fig. 4b shows the hydrodynamic force versus inverse separation distance for fluids of different viscosity based on the measurements by Neto et al. [3]. The predicted drainage force based on the no-slip flow condition is also compared in Fig. 4b. It is clearly evident that the no-slip boundary condition is unable to describe the experimental data. The slip length obtained based on Eiq. (6) and (7) is equal to 4 nm and 12 nm for lower and higher viscosity values respectively. Figure 4c shows the shp length as a function of the approach velocity and fluid viscosity indicating that slip length is a function of both the fluid type, i. e. viscosity, and strain rate, i. e. the approach velocity.

Drainage (forced) Drainage applied to an underground metallic structure by impressed current or by sacrificial anode. 

The foregoing discussion leads to the question of whether actual foams do, in fact, satisfy the conditions of zero resultant force on each side, border, and comer without developing local variations in pressure in the liquid interiors of the laminas. Such pressure variations would affect the nature of foam drainage (see below) and might also have the consequence that films within a foam structure would, on draining, more quickly reach a point of instability than do isolated plane films. 

Drops coalesce because of coUisions and drainage of Hquid trapped between colliding drops. Therefore, coalescence frequency can be defined as the product of coUision frequency and efficiency per coUision. The coUision frequency depends on number of drops and flow parameters such as shear rate and fluid forces. The coUision efficiency is a function of Hquid drainage rate, surface forces, and attractive forces such as van der Waal s. Because dispersed phase drop size depends on physical properties which are sometimes difficult to measure, it becomes necessary to carry out laboratory experiments to define the process mixing requirements. A suitable mixing system can then be designed based on satisfying these requirements. 

Static holdup depends upon the balance between surface-tension forces tending to hold hquiciin the bed and gravity or other forces that tend to displace the liquid out of the bed. Estimates of static holdup (for gravity drainage) may be made from the following relationship of Shulman et al. [Am. Jn.st. Chem. Eng. J., 1, 259 (1955)] ... 

If an adjustable T-R is connected as forced stray current drainage between pipeline and rails and its output voltage is fixed at a definite level, the protection current and the pipe/soil potential can undergo considerable fluctuation. 

Forced drainage Rail fracture, change in tram current supply Locate failure, speak to traffic organization... 

Fig. 14-10 Forced drainage of stray currents and partial cathodic protection of a 110-kV pressurized cable with a low-resistance connection to the station grounds.

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