Water drops, shape

Impingement is corrosion caused by aerated water streams constricting metal surfaces. It is similar to erosion corrosion in which air bubbles take the place of particles. The pits formed by impingement attack have a characteristic tear drop shape. 

In the present paper, interfacial tensions were measured for a number of heavy crude oils at temperatures up to 200°C using the spinning drop technique. However, reliable data cannot be obtained by this or any other drop shape method because of the small density difference between heavy crudes and water which, moreover, tends to decrease as the temperature increases. This problem was overcome by using aqueous D20 instead of H20 as has been previously described [5,8,211. The influence of surfactant type and concentration, mono- and divalent cation concentrations, and pH on the attainment of low interfacial tensions are reported and discussed. 

Fig. 6. Different drop shapes of endotamponade materials in water (a) PFCL, (b) partial fluorinated liquid and (c) heavier than water silicone oil.

Water drops become unstable and tend to break up before they reach 1 cm in diameter (see Chapter 12). Drops approaching this size show periodic shape fluctuations of relatively low amplitude (J3, M4). 

At larger Re and for more marked deformation, theoretical approaches have had limited success. There have been no numerical solutions to the full Navier-Stokes equation for steady flow problems in which the shape, as well as the flow, has been an unknown. Savic (S3) suggested a procedure whereby the shape of a drop is determined by a balance of normal stresses at the interface. This approach has been extended by Pruppacher and Pitter (P6) for water drops falling through air and by Wairegi (Wl) for drops and bubbles in liquids. The drop or bubble adopts a shape where surface tension pressure increments, hydrostatic pressures, and hydrodynamic pressures are in balance at every point. Thus... 

STEP 2 PREPARATION OF THE substrate(s). While ahnost any substrate can be used, we will use glass microscope slides in this example this is a common substrate and makes it easy to see the CdS film. The microscope slide can be cut to whatever size and shape is convenient. The slide should be cleaned well, since films usually do not adhere well to dirty surfaces. Suitable cleaning agents are trichloroethylene or/and sulphochromic acid, and the slide should be well rinsed with pure water. If the slide is clean, water dropped onto it will form a film (hydrophilic surface), while on a dirty (hydrophobic) slide the water will form drops. Needless to say, the part of the slide where deposition is to occur should not be touched with the hands after this treatment. 

FIG. 6.1 Control of wettability of surfaces through chemistry (a) schematic illustration of formation of hydrophobic lines on a hydrophilic surface with self-assembled monolayers (SAMs) and micromachining (b) top view of the shapes and confinement of water drops on an engineered surface. (Reproduced with permission of Abbott et al. 1992.)... 

A drop of water in a body of oil will take the shape which gives the least surface area—this is a sphere. Further, the water drop will squeeze itself in as tightly as possible to reduce its size and therefore its surface as much as possible. The measure of this drop shrinking force is called surface tension... 

FIG. 5.4. Prince Rupert s drops, (a) Shows tire heated glass about to drop into a beaker of water. Typical shapes for tliese drops are shown in (b). 

For comparison, an untreatedfiller (Si02 in the modification of cristobalite, Fig. 9c) shows sharp fracture shapes (white arrow), which differ markedly from those of silicone-enveloped fillers. Furthermore, missing interstitial fillings toward an overlying ground dust (black arrow) indicate that cristobalite was not treated with silicone. On contact with water, the slightly compressed cristobalite powder is wetted immediately (Fig. 9a), and the water drop is absorbed within a few seconds. 

In general, the stronger the attractions between particles, the greater the surface tension. Water has a high surface tension because its molecules can form multiple hydrogen bonds. Drops of water are shaped hke spheres because the surface area of a sphere is smaller than the surface area of any other shape of similar volume. Water s high surface tension is what allows the spider in Figure 13-14b to walk on the surface of a pond. 

Contact Angle Measurements, were obtained with a Drop Shape Analysis System DSA100 (Kriiss GmbH, Hamburg, Germany) using water and diiodomethane as test liquids. The contact angles were measured by the sessile drop method within two seconds. The surface tension y as well as the dispersive and polar components (yD and yp) were calculated based on the Owens-Wendt method [7],... 

Dynamic properties of interfaces have attracted attention for many years because they help in understanding the behaviour of polymer, surfactant or mixed adsorption layers.6 In particular, interfacial rheology (dilational properties) is crucial for many technological processes (emulsions, flotation, foaming, etc).1 The present work deals with the adsorption of MeC at the air-water interface. Because of its amphiphilic character MeC is able to adsorb at the liquid interface thus lowering the surface tension. Our aim is to quantify how surface active this polymer is, and to determine the rheological properties of the layer. A qualitative and quantitative evaluation of the adsorption process and the dilata-tional surface properties have been realised by dynamic interface tension measurements using a drop tensiometer and an axisymmetric drop shape analysis. 

A collaborative effort between The University of Mississippi (Seiner), Florida State University (Krothapalli), and Combustion Research and Flow Technology — CRAFT (Dash) has recently been initiated that includes all phases that are required for completion of a successful noise-reduction program. To enable projection of model-scale laboratory acoustic data to full scale, one-tenth-scale models have been constructed. The primary methods being investigated for noise suppression involve the use of micro-air-jet injection, water-drop injection, and modification of nozzle divergent flaps into corrugated shapes with chevrons. All of these concepts are known to produce little impact on aeroper-formance. 

---