Silence

Nesvijski, E.G., Nogin, S.I. Acoustic Emission Technics for Nondestructive Evaluation of Stress of Concrete and Reinforced Concrete Structures and Materials. Third Conference on Nondestructive Evaluation of Civil Structures and Materials, Boulder, CO, 1996. Nesvijski, E. G. Failure Forecast and the Acoustic Emission Silence Effect in Concrete. ASNT s Spring Conference, Houston, TX, 1997. 

Dual cure sites Ductile iron Ductile particles Duct silencers Dugro [7681-76-7]... 

Most rotating equipment includes electric motors or steam dryers that generate noise at a constant frequency. Air cooler fans are a source of noise that can be reduced by lowering the fan speed and increasing the number of blades. Pump motor noise can be reduced by including a shroud or fan cover that is accurately lined. Centrifugal compressor noise reduction can be achieved by blade design and the use of compressor pulsation noise reduction, silencers, and vibration isolation. 

The most widely used exhaust control device consists of a ceramic monolith with a thin-waHed open honeycomb stmcture. The accessible surface of this monolith system is iacreased by applyiag a separate coatiag, a wash coat, of a high surface area material such as gamma-alumiaa with the catalyticaHy active species impregaated iato this washcoat. The catalyst aeeds to oxidize hydrocarboas, coavert CO to CO2, and reduce NO. The whole system forms a catalytic converter that, suitably encased, is placed between the engine and the muffler/silencer unit. 

The alarm occurrence is acknowledged by the process operator. When all alarms have been acknowledged, the audible annunciator is silenced. 

Another serious distraction to a process operator is the multiple alarm event, where a single event within the process results in iTuuti-ple alarms. When the operator must individually acknowledge each alarm, considerable time can be lost in silencing the obnoxious annunciator before the real problem is addressed. Air-handling systems are especially vulnerable to this, where any fluctuation in pressure (for example, resulting from a blower trip) can cause a number of pressure alarms to occur. Point alarms (high alarms, low alarms, status alarms, etc.) are especially vulnerable to the multiple alarm event. This can be addressed in one of two ways ... 

Thunderous noise during an interruption, because of air blast. The intensity can be controlled by providing silencers... 

Solenoid valve actuator Electric motor, AC A Atmospheric outlet FC Control element closes on failure of auxiliary energy supply FO Control element opens on failure of auxiliary energy supply O Silencer... 

Ail compressor anti-surge (ON - OFF) control circuit, comprising transmitters, computers and pneumatic blo-w-off control valve Reverse flow protection (on axial compressors only) as supplementary protection device against surging, v. orkmg indepenciently of the control ciicuit Blow-off. silencer Expander emergency stop valve with pneumatic actuator and solenoid valve... 

Noise control is worth mentioning. The turboexpander and axial compressors are noise producers and consideration must be given to the need for providing noise abatement. Silencers on vents and noise insulation housings on machines should be considered and have been proven effective. 

Lowering the inlet velocities and providing proper inlet silencers can reduce air noise. Considerable work by NASA on compressor casings has greatly reduced noise. 

The inlet and exhaust systems in gas turbines are described. The inlet and exhaust systems consist of an inlet filter, silencers, ducting, and expansion joints. The design of these systems can be critical to the overall design of a gas turbine. Proper filtration is a must, otherwise problems of blade contamination and erosion ensue. The standards are minimal for specifications. 

Silencers are also minimally specified. Work in this area has progressed dramatically in the past few years with the NASA quiet engine program. There are some good silencers now available on the market, and inlets can be acoustically treated. 

Screw compressors of the dry type generate high frequency pulsations that move into the system piping and can cause acoustic vibration problems. These would be similar to the type of problems experienced in reciprocating compressor applications, except that the frequency is higher. While volume bottles will work with the reciprocator, the dry type screw compressor would require a manufacturer-supplied proprietary silencer that should take care of the problem rather nicely. 

With alarm management, the high pressure trip would alarm, but the other associated alarms would be suppressed, since they are the expected result of the high pressure trip. On the other hand, a low flow condition from a different cause would be alarmed. Plants with managed alarms are inherently safer than those without since it is easy to silence and overlook a critical alarm in the midst of an alarm shower. However, the benefits should be balanced with the increased complexity and maintenance requirements. 

Figure 4-68. Typical blower intake filter-silencer. Air to blower leaves through pipe connection, which may be screwed or flanged. Courtesy of Dollinger Corp.

Aftercondensers operate at atmospheric pressure. They do not affect the steam economy or ejector performance, but they do avoid the nuisance of exhausting steam to the atmosphere, thus, they allow steam to be recovered. They also serve as silencers on the ejectors, and with barometric types they can absorb odors and corrosive apors. 

For atmospheric air intake, an air filter and silencer are usually required. The air filter is to keep out dirt in the air the silencer is to reduce the local noise level. 

Figure 15.29 The layout of a typical diesel generator engine room. 1 Diesel generator set 2 jacket water header tank 3 lubricating oil service tank 4 air receiver 5 diesel-driven compressor 6 batteries and charger 7 engine control panel 8 pneumatic control panel 9 fuel oil control panel 10 engine exhaust silencer 11 charge air filter 12 daily service fuel oil tank 13 three-section radiator...

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