Surface rippling

In addition to the deformation modes described above, there are some other modes of practical interest, for example, the cyclic spreading, recoiling, and oscillation mode typical of solder jetting process.[5°1 This mode leads to a final splat shape of multiple surface ripples at low substrate temperatures and hemispherical shape without surface ripples at high substrate temperatures. 

An indication of such a morphological transition is a pronounced enhancement of oxide film roughness at a thickness of 11 nm, observed by AFM, as shown in Fig. 5.5. The appearance of this surface ripple corresponds to the first potential peak in Fig. 5.4. An investigation using differential IR spectroscopy revealed that the peak position, width and degree of symmetry of the Si-O absorption bands... 

Crystals are often associated with their unique polyhedral shapes. Their smooth, shining facets provide a constant source of fascination to ancient, arid modem beings alike. Advances in microscopy have not, tainted the myth a bit interesting surface stmctures are found down to the atomic level, be it surface reconstmction, surface ripples and dimples, or snow-flakish fractals... 

Agitators capable of level 6 will Blend miscible fluids to uniformity, if specific gravity differences are less than 0.6 and if the viscosity of the most viscous is less than 10,000 times the viscosity of the other Suspend trace solids (<2%) with settling rates of 2-4 ft/min Produce surface rippling at lower viscosities. 

It must be self-healing since surface ripples will disrupt the monolayer. This implies viscous rather than rigid monolayers. 

Konobeev et al. (K21), 1961 Experimental study of C02 absorption by water film, with upward and downward cocurrent gas/film flow, inside tubes 1.05-1.66 cm. i.d., 20-87 cm. long. Gas velocities 6-86 m./sec. IVko = 5-105. Length and amplitude of surface ripples and local film thicknesses measured. Rate of mass transfer stated to be function of wave characteristics only. 

In general, the observed mass-transfer rates are greater than those predicted by theory and may be related to the development of surface rippling, a phenomenon which increases in intensity with increasing liquid path. 

The annual loss of water from hot country lakes and reservoirs due to evaporation is usually about 3 m per year. This evaporation can be reduced considerably by coating the water surface with an insoluble monolayer for example, a monolayer of cetyl alcohol can reduce the rate of evaporation by as much as 40 per cent. Insoluble monolayers also have the effect of damping out surface ripples. 

Figure 21.3 Molecules in air strike a surface at a rate directly proportional to the surface area. (A) The surface area is easier to estimate for a smooth surface. (B) Real surfaces often have surface ripples at any arbitrary level of magnification, making it more difficult to estimate the surface area.

Entrainment and Mechanical Disintegration Gas can be entrained into a liquid by a solid or a stream of liquid falling from the gas phase into the liquicl, by surface ripples or waves, and by the vertical swirl of a mass of agitated hquid about the axis of a rotating agita-... 

Houssiau and Bertrand [89] refined the model by introduction of a small surface rippling by reason of an outward shift of the Au atoms by 12 pm, which is also in good comparison with the outward shift of Au by 9 pm for the (110)... 

Moreover, the cooling rate also influences the quality of the epitaxial layer Solvent inclusions and surface ripples appear when cooling rate is above... 

Figure 5.B-9 shows effective interfhcial areas that were deduced by Shulman et al.N from experiments on tha sublime ion of naphthalene Rase hi g rings. Many other studies have been inede in na attempt to relate effective area to specific packing surface, as a function or liquid and vapor flow rates. Generally, it is thought that the effective area reachas the specific area near the onset of flooding, but Pig. 3.8-9 shows that this mey not be the case. It also should be noted that the total area available for main transfer includes film surface ripples, entrained liquid within the bed, and vapor bubbling through pockets of liquid held up in the bed. Another important point relative specific surface of differeat packings might indicate relative mass transfer efficiencies, but this Is often sot the case.

By inspection of (5.8), (5.14), (5.15), (5.17), and (5.18) it is clear that the surface displacements show the same wave character as and This means that as far as the dynamics of the surface waves are concerned, we are interested only in the dependence of u on the system variables, since completely determines the time dependence of the surface ripples. 

Intensity fluctuation spectroscopy was used in our laboratory to study the dynamic behavior of surface ripples on thin liquid films. Both squeezing and bending modes were examined. To our knowledge one other group of researchers has obtained dynamic light-scattering data from thin soap films but as far as we know, nothing has been published in the official literature. Also some experiments were reported on lipid bilayers in water. ... 

For large values of Re, the result is Eq. (15=40c). Thus, both analyses agree for short contact times. For long contact times (Re < 100 and large L) the average mass-transfer coefficient and Sherwood number for a system with no surface ripples are... 

The results in Eqs. ri5-40cl and fl5-43bl assume that the flow is laminar and the gas-liquid surface is flat. At Reynolds numbers less than 250, the flow is laminar f Sherwood et al 19751. However, even if the fluid flow remains laminar, ripples can appear on the surface. Ripples cause local mixing, which increases the liquid-side mass-transfer coefficient markedly. On the other hand, the area for mass transfer increases only slightly. If even small quantities of surfactant (e.g., soap or proteins) are added, the ripples are eliminated and the previously derived correlations for k, ijq remain valid. 

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