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Fan Silencers

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CFS Series Fan Silencer

INFORMATION ON FAN SILENCERS
Industrial fan installations, small or large, produce noise. This fan noise is one of the most predominant noise sources in an industrial plant. The magnitude and intensity of noise will vary depending on fan size, horse power, air flow, type and number of blades, static pressure, rotational speed, etc.

Fans normally deliver a large volume of air at relatively low static pressures usually measured in inches of water. The rotating action of vanes produce a broad band noise spectrum however, the noise in mid to high frequency range is heard to be louder and requires to be treated for achieving noise control.

Generally, silencers are used at intake and discharge of fan installations for treating air borne noise. Fan silencers usually require absorptive type design as they are well known for better attenuation in mid and high frequency range (500-8000 Hz). The effectiveness of absorption material progressively reduces at frequencies above and below this range.

The noise control is achieved by means of absorption. The acoustic energy propagating through the silencer is effectively absorbed into the fiberous absorption material and converted into heat energy. These silencers generally employ straight thru design and has a low pressure drop as it imposes very little restriction to the flow.

SILENCER SELECTION
The fan silencers are normally selected on the basis of maximum allowable pressure drop at rated flow and the silencing criteria. These silencers are usually sized for around 5000 to 5500 FPM velocity but not exceeding 7500 FPM velocity to prevent excessive self generated noise and aerodynamic noise generation. While selecting the fan silencer, it must be ensured that the flow area throughout the silencer is sufficient to accomodate the air flow without imposing excessive restriction.

The following table indicates the maximum recommended air flow in CFM for respective silencer size in accordance with the above guidelines.

chartb

Select the silencer size based on the air flow from the above table.

Refer to the formulas given here for calculating the pressure drop for the silencer size selected. Check this pressure drop against the maximum allowable pressure drop. If the pressure drop is too high, select the next larger size and recalculate.

PRESSURE DROP
(These calculations assume air as the flowing gas. For other gases, density and other corrections may be required. Contact our engineers for assistance).

calc4Data Required:
• 
Air Flow Rate (Actual CFM)
• Temperature (°F)
• Pressure (PSIG)
• Maximum allowable pressure drop (inches of water)

If this pressure drop is higher than the maximum allowable pressure drop, then select next larger size and recalculate.

TEMPERATURE LIMITS
Various options for acoustical absorption materials are available with temperature limits ranging from 325°F to 1000°F. Please consult our engineers for your specific applications for selecting suitable absorption material suiting to your requirements.

PRESSURE RATING
The silencers described herein are designed to a maximum operating pressure of 15 PSIG. For applications where pressure exceeds 15 PSIG, the silencers can be designed to ASME Code, Section 8, Div. 1 for pressure vessel construction. The dimensions are similar to standard models, but the material type and thicknesses are selected to meet code requirements. Consult our engineers for pricing and design information.

ATTENUATION CURVES
Noise attenuation curve showing insertion loss at each frequency is shown here. This represents the insertion loss for airborne noise under average conditions. The resultant silenced noise level will depend on a number of other factors therefore this curve should be used with discretion and can be used as a guideline for evaluating the noise levels after the silencer installation.

We specialize in custom designs and also provide various nozzle orientations to suit your specific requirements.


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