Surface skin effect

Depending on the position of the inductor in or at the mold, the required cavity temperature can be generated near the surface (skin effect). This offers the advantage that much lower amounts of heat are introduced into the mold. In fluid-based temperature control systems, the heat has to be transferred from the interior of the mold in the cavity direction. Therefore, larger mold parts are accidentally heated as well. 

Exciting developments based on electromagnetic induction raced along from that time, giving us the sophisticated products our everyday lives depend on. During most of the period productive uses for eddy current technology were few and few people believed in it as a usefiil tool eddy currents caused power loss in electrical circuits and, due to the skin effect, currents flowed only in the outer surfaces of conductors when the user had paid for all the copper in the cable. The speedometer and the familiar household power meter are examples of everyday uses that we may tend to forget about. The brakes on some models of exercise bicycle are based on the same principle. 

Moisture. Absorbed and retained moisture, especially as ice, has a significant effect on the stmctural and thermal properties of insulation materials. Most closed-ceU plastic foams have low permeance properties most notably where natural or bonded low permeance surface skins exist (29,30). Design, building, and constmction practices requite adequate vapor retarders, skins, coatings, sealants, etc, in order to prevent the presence of moisture. However, moisture vapor cannot be completely excluded, thus the possibiUty of moisture absorption and retention is always present. The freezing of moisture and mpturing of cells result in permanent reduction of thermal and stmctural performance. 

Erequencies from 1 kHz to 50 MHz are used for various appHcations (3). Ferromagnetic materials have a skin-effect response to eddy currents which restricts the penetration depth. Nonferromagnetic materials on the other hand can be inspected to greater depth. In 6061-T6 aluminum, for example, a cod having a 1-kHz frequency effectively penetrates the surface to a depth of 3.2 mm (1). The same probe in steel penetrates to a depth of 0.5... 

Skin effect - the same theory is usually true for the skin effect. The thinner the surface, the smaller will be the nucleus resulting in a higher concentration of current at the surface and better utilization of metal. 

The ac resistance increase due to skin effect given above should be considered as a minimum. When wires are placed next to one another and placed in layers within a transformer, the near field magnetic effects between wires further crowd the current density into even smaller areas within the wire s cross-section. For instance, when wires are wound next to one another, the current is pushed away from the points of contact along the surfaces of the wires to areas orthogonal to the winding plane. When layers are placed on top of one another the inner layers show much greater degradation in apparent resistance than do the outermost layers. 

Air-gas drilling usually increases drilling rate by three or four times over that when drilling with mud as well as one-half to one-fourth the number of bits are required. In some areas drilling with air is the only solution these are (1) severe lost circulation, (2) sensitive producing formation that can be blocked by drilling fluid (skin effect), and (3) hard formations near the surface that require the use of an air hammer to drill. 

Resistance to puncture is another type of loading. It is of particular interest in applications involving sheet and film as well as thin-walled tubing or molding and other membrane type loaded structures. Hie surface skins of sandwich panels are another area where it is important. A localized force is applied by a relatively sharp object perpendicular to the plane of the sheet of material being stressed. If the material is thick compared to the area of application of the stress, it is effectively a localized compression stress with some shear effects as the material is deformed below the surface of the sheet. 

Surface skin cleansing with soap and water has a relatively small effect on acne because it has minimal impact within follicles. 

Temperatures much above 100° C can best be attained by heating the electrode alone by means of supplemental ac currents. Owing to the skin effect, such currents (at sufficiently high frequencies) travel along the metal surface and hence make the necessary power load for heating relatively small (Velev, 1990). 

ASTM D575105 does not primarily recommend the generation of a stress/strain curve but details two methods - force at given deflection and deflection at given force. The test piece is a cylinder 28.6 0.1 mm diameter and 12.5 0.5 mm thick from which all moulded surface layers have been removed. The removal of moulded surfaces is presumably to eliminate skin effects, although such effects, if significant, would be present in a moulded product and one would expect to test in the same condition. 

Equation (5.4) is valid as long as the skin depth is large in comparison to the mean free path of the electrons in the metal. This holds true in the microwave range at room temperature, for cryogenic temperature the surface resistance lies above the values predicted by Equation (5.4) and exhibits a f2 3 rather than a f1 2 frequency dependence (anomalous skin effect [7]). 

According to this concept, the stabilizer function of alumina reduces to paracrystal-line lattice defects an analogous effect is to be expected with Cr203, Sc203, etc. [262], [296]. Another theory is based on the observation that during reduction part of the alumina precipitates with other promoters into the surface of the iron crystallite in a molecularly dispersed distribution [258], [297] or in small islands [254]. This patchy monolayer of alumina acts like a spacer between iron atoms of neighboring crystallites and prevents sintering by means of a skin effect [263]. (See also [101], [110], [253].)... 

A good example to explain this impetus is the shark skin effect. The scales of predatory fishes have fine longitudinal grooves that cause less cross-flow in the displaced water. This principle has been adapted to aeroplane surfaces to help to reduce fuel consumption by 1 %. Similar shark skin swimsuit surfaces allow competitive swimmers to enjoy the advantages of lower resistance to movement through the water. 

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