o_191ln0gpf9pgfdj4601afj5gva.pdf

Gas Turbine Acoustics and Noise Control 161
Table 10-4. General Uses and Properties of Acoustical Materials
————————————————————————————————————
Silencer Acoustical Retainer Temperature Thermal Durability Resistance to
Application Material Material Range Cycling Friability [1]
————————————————————————————————————
Mineral Wool Cloth Mesh [2] N/A N/A Good Good
Inlet
Fibrous Glass Cloth Mesh [2] N/A N/A Good Good
Blanket/Batt
————————————————————————————————————
Mineral Wool Wire Mesh ~ 800°F Good Moderate Moderate
Ceramic Wire Mesh ~ 2,000°F Excellent Poor [3] Low [3]
Exhaust Basalt Wire Mesh ~ 1,400°F Poor [4] Good [4] Moderate
Fibrous Glass Wire Mesh 1,000°F Good Good Moderate
Blanket/Batt
typical limit
————————————————————————————————————
Notes: [1] Friability—the propensity to breakdown or disintegrate.
[2] A very low flow resistance is required to maintain performance.
[3] Packing of material and low vibration critical for longevity.
[4] Protective thermal shock blanket required for longevity.
The perforated sheet should have an open ratio greater than
35% for inlet applications and greater than 25% for exhaust applications.
Table 10-4 provides a general guideline as to choice and
applicability of materials. The user should always verify material
properties.
Exhaust system temperatures can be in excess of 540º C
(1,000ºF), which calls for the careful selection of materials. Wire
mesh is used in exhaust for material retention because at high
temperatures the cloth materials begin to melt and fuse forming a
glass sheet that degrades the silencer’s ability to attenuate noise. Too
heavy or too tightly weaved retainer cloth can degrade performance
dramatically and the challenge is to find a cloth suitable for retaining
the filler material while still allowing the acoustical sound wave
to penetrate the cloth. Mineral wools typically have binders that
breakdown at about 425º C (800ºF), which causes the material to be
blown out the exhaust. Thermal cycling (start-stop of the turbine)