Static pressure, effect

Hermans, T Vrielynck, M. Static pressure effects on photographic materials. Part III. The influence of dyes. J. Photogr. Sci. 1984, 52, 153-157. 

Sonochemistry is strongly affected by a variety of external variables, including acoustic frequency, acoustic intensity, bulk temperature, static pressure, ambient gas, and solvent (47). These are the important parameters which need consideration in the effective appHcation of ultrasound to chemical reactions. The origin of these influences is easily understood in terms of the hot-spot mechanism of sonochemistry. 

Disjoining Pressure. A static pressure difference can be imposed between the interior and exterior of a soap film by several means including, for example, gravity. In such cases the equiHbrium film thickness depends on the imposed pressure difference as weU as on the effective interface potential. When the film thickness does not minimize lV(f), there arises a disjoining pressure II = —dV/(U which drives the system towards mechanical equiHbrium. 

Cavitation. The subject of cavitation in pumps is of great importance. When the Hquid static pressure is reduced below its vapor pressure, vaporization takes place. This may happen because (/) the main stream fluid velocity is too high, so that static pressure becomes lower than vapor pressure (2) localized velocity increases and static pressure drops on account of vane curvature effect, especially near the inlets (J) pressure drops across the valve or is reduced by friction in front of the pump or (4) temperature increases, giving a corresponding vapor pressure increase. 

Disturbances upstream of the probe can cause large errors, in part because of the turbulence generated and its effect on the static-pressure measurement. A calming section of at least 50 pipe diameters is desirable. If this is not possible, the use of straightening vanes or a honeycomb is advisable. 

Explosion venting is always accompanied by flame propagation plus pressure consequences in the surrounding areas. Tne flame length will be larger with a lesser static activation pressure and smaller vent area. Depending on the volume of the protected equipment, it can reach up to 50 m. The pressure effect in the vicinity of the vent area is... 

Set Pressure - The set pressure (the pressure at whieh the PR valve is designed to open) is speeified in accordance with Code requirements. In most vessel apphcations, the set pressure of at least one PR valve is equal to the design pressure. However, this set pressure is adjusted (up or down) for any effect of static pressure and friction pressure drop that may apply when the valve is installed elsewhere than directly on the vessel. For example, if a PR valve is installed in a non-flowing line above a liquid-filled vessel, the PR valve set pressure would be reduced sufficiently to allow for the liquid static head between the vessel and the valve. 

When a PR valve is relieving at rated capacity, the total frictional pressure drop between a vessel and the inlet of the valve should be less than 3% of the set pressure (kPa). In this calculation, the effect on static pressure of fluid acceleration is ignored rather, only friction loss is considered. 

The airflow rate Q, for each air leakage path is expressed with Eqs. (7.237), (7.242), and (7.243) using the infotmation on effective leakage area, CjA, and a pressure difference across the path. The total pressure acting on an opening from the outside is the sum of the pressure due to wind, gravity forces, and mechanical ventilation performance, and the static pressure inside the building results from Eq. (7.244). 

Static pressure difference between two zones resulting from the wind effect on the building envelope (Fig. 7.108fe). 

Instrument for measurirtg effective static pressure in duct... 

Instrument for measuring effective static pressure at gas-metenng device. 

Coanda effect When a jet becomes and remains attached to a surface due to static pressure differences, as in the case of a wall jet. 

Example 3-2 Illustrating Static, Pressure, and Friction Effects... 

Figure 12-136A, B. Effects of fan dampers on airflow, static pressure, and brake horsepower. (A) Backwardiy inciined fan with outiet damper. (B) iniet damper appiied to condition of (A). (Used by permission Engineering Letter No.11, 1996. The New York Biower Co. For more information, contact the company at www.nyb.com.)...

Figure 12-138A, B, C, D. Centrifugal fan system control methods. Note the effect of air distribution zone control (A for VAV) terminal on sudden jump in system resistance to fan operating static pressure curve. (Used by permission Haines, R. W. Heating/Piping/Air Conditioning, p. 107, Aug. 1983. Penton Media, Inc. All rights reserved.)...

The effect of density of the air or gas entering the suction of the second (and/or third, etc.) fan is significant for high-pressure units operating individually above about 15 in. of water static. The static pressure rise in the second fan corrected for suction pressure is as follows, neglecting losses. ... 

The effect of nucleating sources is important when attempting to scale studies with models tO full-size components. A common practice in model tests is to expose the fluid to a high static pressure prior to testing in order to drive free gas into solution. In contrast the seeding of water tunnels is considered to improve scaling particularly in high-speed propeller applications . 

These two disturbances cause errors in opposite directions, and the static pressure should therefore be measured at the point where the effects are equal and opposite. 

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