Surface treatment waviness

From the brief discussion above it is apparent that the flow of viscous liquids in the form of thin films is usually accompanied by various phenomena, such as waves at the free surface. These waves greatly complicate any attempt to give a general theoretical treatment of the film flow problem Keulegan (Kl4) considers that certain types of wavy motion are the most complex phenomena that exist in fluid motion. However, by making various simplifying assumptions it is possible to derive a number of relationships which are of great utility, since they describe the limits to which the flow behavior should tend as the assumptions are approached in practice. 

In addition to the theories reviewed above, there are many treatments in the literature which deal with the hydraulics of wavy flow in open channels. Most of these refer to very small channel slopes (less than 5°) and relatively large water depths. Under these conditions, surface tension plays a relatively minor part and is customarily neglected, so that only gravity waves are considered. For thin film flows, however, capillary forces play an important part (K7, H2). In addition, most of these treatments consider a turbulent main flow, while in thin films the wavy flow is often... 

The problem of turbulent flow in thin films has received comparatively little attention. Because of the great complexity of the flow processes involved, there are no theoretical treatments of the problem of wavy turbulent flow, and the usual procedure is to neglect the surface waves and obtain solutions for the case of smooth turbulent flow. 

Semenov (S7) simplified the wavy flow equations by omitting the inertia terms, which is permissible in the case of very thin films. Expressions are obtained for the wavelength, wave velocity, surface shape, stability, etc., with an adjoining gas stream the treatment refers mainly to the case of upward cocurrent flow of the gas and wavy film in a vertical tube. 

On the theoretical side, Dmitriev and Bonchkovskaya (D8) have shown that in principle turbulence should spread from waves. Kapitsa (K9) has calculated a general tensor quantity, termed the coefficient of wavy transfer, which is applicable to any flow with periodic disturbances, such as pulsations or surface waves. This treatment predicts an appreciable increase in the rates of heat and mass transfer in wavy films, though this increase does not appear to be as large as that observed experimentally under certain conditions. 

Before introduction of hemodialysis in the treatment of chronic renal patients, the kidneys of patients who died of Balkan nephropathy used to be the smallest seen at post mortem examinations, weighing 14.8-80 g each (Figure 2A) the difference between the left and right kidneys being small (5-20 g) [74, 76-78]. Surface of the kidneys is smooth, occasionally wavy but never granulated or roughly nodular. The section shows markedly narrowed cortex, pyramid and Bertin s columns are fairly well preserved, and corticomedular border is well differentiated. Papillary necrosis of the pyramids has not been found. 

Depending on material and treatment, the surface can be an insulator, a semiconductor or a conductor. Technically produced surfaces are flat or curved. A distinction is made between flatness, waviness and roughness. The surfaces contain defects on an atomic and on a macroscopic scale. Such atomic defects are point defects,... 

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