Thin layers, rotational viscosity

By the total internal reflection condition at the liquid-liquid interface, one can observe interfacial reaction in the evanescent layer, a very thin layer of a ca. 100 nm thickness. Fluorometry is an effective method for a sensitive detection of interfacial species and their dynamics [10]. Time-resolved laser spectrofluorometry is a powerful tool for the elucidation of rapid dynamic phenomena at the interface [11]. Time-resolved total reflection fluorometry can be used for the evaluation of rotational relaxation time and the viscosity of the interface [12]. Laser excitation can produce excited states of adsorbed compound. Thus, the triplet-triplet absorption of interfacial species was observed at the interface [13]. 

In some foods, a thin layer of low-viscosity fluid forms at the solid-fluid interface that in turn contributes to lower viscosity values. The boundary condition that at the solid-fluid interface the fluid velocity is that of the wall is not satisfied. This phenomenon is known as slip effect. Mooney (1931) outlined the procedures for the quantitative determination of slip coefficients in capillary flow and in a Couette system. The development for the concentric cylinder system will be outlined here for the case of the bob rotating and details of the derivation can be found in Mooney (1931). 

Another problem, similar in character to the one considered above, is the problem of cavitation in a thin layer between two rotating cylinders [18]. Rotation of two cylinders leads to an outflow of viscous liquid from the tank, which is accompanied by the formation of a thin moistening layer at the surface of the cylinders. The clearance between the surfaces of cylinders is small therefore the flow in the formed film is driven by the forces of viscosity and surface tension. In the clearance between cylinders, the liquid flows parallel to the surface. The character of the flow is same as in a film at the surface of a plate being removed from the tank. 

These experiments leave, one sees, no doubt about the existence, in the surface layer of water, of intrinsic viscosity, much higher than viscosity of the interior of same liquid, and if one considers that the thickness of the surface layer of a liquid is equal to the sensible radius of activity of the molecular attraction and consequently of an excessive smallness, one will have to conclude from the facts above that the intrinsic viscosity of the surface layer of water is extremely large. Let us notice here that this so thin layer must involve in its rotation the Uquid under unclaimed until a certain depth, so that the total mass which turns much exceeds that of the layer in question that is what explains how this mass can acquire enough speed to carry the needle beyond the magnetic meridian line. Let us add that, in consequence of its excessive thinness, the surface layer could probably only oppose, by itself, a low resistance to the movement of the needle, and that most of the resistance observed must be due to the drive of the mass in question. 

Effect of Fluid Viscosity and Inertia The dynamic effect of viscosity on a rotating liquid slurry as found in a sedimenting centrifuge is confined in veiy thin fluid layers, known as Ekman layers. These layers are adjacent to rotating surfaces which are perpendicular to the axis of rotation, such as bowl heads, flanges, and conveyor blades, etc. The thickness of the Ekman layer 6 is of the order... 

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