Sharp edges

Figure 4 Virtual source distribution for a sharp-edged flaw.

Fligh-tech ceramics withstand great mechanical stresses even thin structures and sharp edges are feasible with high reliability. This allows connecting the HT cables reliably to the ceramic part of the tubes directly. Many available resin systems bond easily to ceramics. 

In practice, it may be possible with care to float somewhat larger particles than those corresponding to the theoretical maximum. As illustrated in Fig. XIII-7, if the particle has an irregular shape, it will tend to float such that the three-phase contact occurs at an asperity since the particle would have to be depressed considerably for the line of contact to advance further. The resistance to rounding a sharp edge has been investigated by Mason and co-workers [62]. 

Magnification of a sharp edge showing the many tips and valleys on a molecular scale. 

A second important need for some guidance system lies in stray electric fields. Clearly, a sufficiently large potential arranged transversely to an ion beam can serve to deflect ions away from the intended direction. Such stray fields can be produced easily by sharp edges or points on the inside of a mass spectrometer and even more so in an ion guide itself. Considerable care is needed in the construction and design of mass spectrometers to reduce these effects to a minimum. 

Similarly, a sharp edge (razor blade) or a very sharp curve can also provide an intense electric field. For any given electric potential, as the radius of curvature of a tip or edge becomes smaller, the electric field becomes increasingly stronger. 

By growing thin whiskers along a sharp edge or thin wire, the ends of the whiskers become regions of very small radius of curvature and, consequently, provide very intense electric fields. 

The wedge restriction has no critical surface dimensions or sharp edges and tends to retain accuracy despite visible corrosive or erosive wear. It is commonly appHed to high viscosity Hquids, slurries, and hot multiphase mixtures. A similar device is also available using a cone, positioned so that its large diameter is upstream, mounted on the meter centerline. 

Although the above description has concentrated on separation from a smooth surface, separation also occurs at sharp edges. Where separation is undesirable for a process reason, it can often be eliminated by redirecting the flow using turning vanes, ie, forcing it to hug the surface. 

Fig. 5. Entrance flows in a tube or duct (a) separation at sharp edge (b) growth of a boundary layer (illustrated for laminar flow).

In one extractor (FMC Inc.), the fmit is located between two cups having sharp-edged metal tubes at their base. The upper cup descends and the many fingers on each cup mesh to express the juice as the tubes cut holes in the top and bottom of the fmit. On further compression, the rag, seeds, and juice sacs are compressed into the bottom tube between the two plugs of peel. A piston moves up inside the bottom tube forcing the juice through perforations in the tube wall. A simultaneous water spray washes the peel oil expressed during extraction away from the peel as an oil—water emulsion the peel oil is recovered separately from the emulsion. 

A considerable reduction in stress concentration could be achieved by using a cross-bore which is eUiptical in cross-section, provided the major axis of the eUipse is normal to the axis of the main cylinder. A more practical method of achieving the same effect is to have an offset radial hole whose axis is parallel to a radius but not coincident with it (97,98). Whenever possible the sharp edges at the intersection of the main bore with the cross bore are removed and smooth rounded corners produced so as to reduce the stress raising effects. 

The substrate has to be prepared for cementation. The surface must be clean and free of oxide. Corners and edges are particularly important in diffusion-type coatings sharp edges are usually detrimental. Barrel finishing, ie, tumbling in a barrel with abrasive media, may result in the desired shape. 

After the plates have been washed and dried thoroughly, they are pressed ia a preliminary operatioa to the desired thickness. Iadividual electrodes are thea cut from the sheets and a secondary pressing operation to final thickness is done. Often a secondary operation is required to remove sharp edges of electrodeposited 2iac electrodes. 

Powder coatings as a class are superior to Hquid coatings in abiHty to coat sharp edges and isolate the substrate from contact with corrosive environments. PVC coatings are softer and more flexible than any of the other powder coating materials. Primers used for PVC plastisols have been found generally suitable for powder coatings as weH (5). 

Dental abrasives range in fineness from those that do not damage tooth stmcture to those that cut tooth enamel. Abrasive particles should be irregular and jagged so that they always present a sharp edge, and should be harder than the material abraded. Another property of an abrasive is its impact strength, ie, if the particle shatters on impact it is ineffective if it never fractures, the edge becomes dull. Other desirable characteristics include the abiUty to resist wear and solvation. 

Example 5 Entrance Loss Water, p = 1000 kg/m, flows from a large vessel through a sharp-edged entrance into a pipe at a velocity in the pipe of 2 m/s. The flow is tiirhiilent. Estimate the pressure drop from the vessel into the pipe. 

The orifice coefficient deviates from its value for sharp-edged orifices when the orifice wall thickness exceeds about 75 percent of the orifice diameter. Some pressure recovery occurs within the orifice and the orifice coefficient increases. Pressure drop across segmental ori-fiees is roughly 10 percent greater than that for concentric circular orifices of the same open area. 

Orifice Meter The most widely used flowmeter involves placing a fixed-area flow restriction (an orifice) in the pipe carrying the fliiid. This flow restriction causes a pressure drop that can be related to flow rate. The sharp-edge orifice is popular because of its simplicity, low cost, and the large amount of research data on its behavior. For the orifice meter, the flow rate for a liquid is given by... 

---