Air pocket, trapped

Inlet Piping Configurations. An incorrect piping configuration can create undesirable flow distortions that, especiaUy for double-suction pumps, means turbulence. Air pockets trapped in the pipe can cause uneven flow, vibrations, and pump damage. 

Cavitation is the formation of gaseous cavities in a medium upon ultrasound exposure. The primary cause of cavitation is ultrasound-induced pressure variation in the medium. Cavitation involves either the rapid growth and collapse of a bubble (inertial cavitation) or the slow oscillatory motion of a bubble in an ultrasound field (stable cavitation). Collapse of cavitation bubbles releases a shock wave that can cause structural alteration in the surrounding tissue [13]. Tissues contain air pockets trapped in the fibrous structures that act as nuclei for cavitation upon ultrasound exposure. The cavitational effects vary inversely with ultrasound frequency and directly with ultrasound intensity. Cavitation might be important when low-frequency ultrasound is used, when gassy fluids are exposed, or when small gas-filled spaces are exposed. 

This micro device consists of a square micro chamber which has as a bottom plate a conventional DNA micro-array chip sealed by a cover slip with double-sided adhesive tape (see Figure 1.26) [24], The adhesive tape serves as a spacing gasket to define the shape and dimensions of the chamber. The cover slip contains the air pockets with a uniform, pitched distribution. The air pockets trap the air bubbles... 

FIGURE 9.7. Apparent contact angle on an ideal rough surface as a function of roughness. There is a discontinuity of the contact angle at the threshold for air pocket trapping. 

The caisson followed immediately on experiments with diving bells. Engineers used air pockets trapped beneath heavy containers to inspect submerged sites. Salvage experts and treasure seekers began to delve beneath the ooze. 

Backwashing - After exhaustion, the bed is backwashed to effect a 50 percent minimum bed expansion to release any trapped air from the air pockets, minimize the compacmess of the bed, reclassify the resin particles, and purge the bed of any suspended insoluble material. Backwashing is normally carried out at 5-6 gpm/ft. However, the backwash flow rates are directly proportional to the temperature of water. 

Air pockets or bubbles are left on the surface of all concrete. Good vibration and placing techniques will reduce their number but not eliminate them. Many air pockets have a small opening on the surface in relation to their size. Paints will not penetrate into such holes, with the result that air or solvent is trapped and subsequent expansion will cause the coating to blister. In addition, some air pockets are covered with a thin layer of cement that also has no strength and will cause loss of adhesion. 

In cases where corner joints are unavoidable while constructing tanks, it is necessary to ensure that there are no air pockets, pits or surface irregularities at weld joints to avoid possibility of air trap between the rubber lining and the metal surface. For this, suitable vent holes are to be provided. A typical method of avoiding air being trapped in weld joints is shown in figures 6.6 A, B, C and D. 

The lower the surface free energy of the shell chemistry, the smaller is the contact angle hysteresis on the closely packed surface arrays. Further the contact angles varied with increasing height roughness. A possible explanation for this behaviour is that the vertical roughness influences the curvature radius of the liquid in trapped air pockets at the solid-liquid interface as was already assumed in the literature for nanostructured metal surfaces and paraffin-coated steel balls. 

Sites which trap cold air, because of woods, hollows, valleys, groups of buildings, railway embankments, etc., should be avoided. The nature of the terrain must therefore be taken into account, in order to decide whether the site under consideration lies in a cold air pocket. Wind is an important factor in this respect. Moderate air movement is beneficial cold air which is moving seldom leads to frost damage ... 

Collapse of cavitation bubbles releases a shockwave that can cause structural alteration in the surrounding tissue. Tissues contain air pockets that are trapped in the fibrous structures and act as nuclei for cavitation upon US exposure. The cavitation effect varies inversely with US frequency and directly with US intensity. 

Air may not immediately be thought of as a contaminant, but the presence of air in its various forms may have an impact on the ability of the lubricant to perform its design function. Almost all lubricating oil systems contain some air. Air is found in four phases free air, dissolved air, entrained air, and foam. Free air is trapped in a system, such as an air pocket in a hydraulic line, and may have minimal contact with the fluid. It can be a contributing factor to other air problems when lines are not bled properly during equipment startup and free air is drawn into circulating oils. 

Most practitioners deflne the flow behavior of polymers based on the melt flow index however, this property is not entirely relevant to the rotational molding process because it is essentially a shear-free and pressure-free process. The use of zero-shear viscosity has been proposed as a better way to assess the coalescence behavior of resins. Resins with lower zero-shear viscosity coalesce at a faster rate and can thus be processed using a shorter molding cycle.The coalescence of individual powder particles is initiated as the particles stick and melt onto the mold surface or melt front. As the melt deposition process continues, pockets of air remain trapped between partially fused particles and lead to the formation of bubbles. In the rotational molding process, the coalescence of particles occurs at a temperature range close to the melting point of the material thus, from a processing standpoint, low values of zero-shear viscosity at low temperatures (i.e., close to the temperature at which the particles adhere to the mold surface) are preferable. 

It is not only gas bubbles inside the liquid explosive which may produce this effect. Let us say for example that one has placed a large drop of nitro onto a smooth steel surface. If one were to then strike this drop with a hammer that had a few small pits in its surface, the force required to detonate the drop of nitro would be much less than if the surface of the hammer was smooth. The pits on the hammer surface trap air pockets, which then compress and act the same as gas bubbles inside the explosive itself. 

The silica-based mineral opal may be considered a solid emulsion when enough water is trapped to have microscopic domains larger than the usual hydration layer. A solid foam coffee cup, thermos, or packing filler is made from polymer expanded with microscopic air pockets. Porous polymer and ceramic mem-... 

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