Monday, November 23, 2009
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As discussed in "Measures & Technique In Eliminating / Minimizing PWL", one of the measures to reduce Sound Power Level (PWL) at sources PWL is to split the flow. Half the original flow would result approximately 3 dB reduction. This post will discuss how this 3 dB reduction is derived.
A common acceptable method to predict Sound Power Level (PWL in dB) of AIV source is as follow :
A common acceptable method to predict Sound Power Level (PWL in dB) of AIV source is as follow :
Refer to "Sound Power Level (PWL) Prediction from AIV Aspect" for more discussion on above equatio.
Above equation will provide PWLW for a stream with W mass flow. If the stream is split into two stream, the mass flow will be W/2.
Sound Power level for single half-stream (W/2),
PWLW/2 = PWLW + 10Log [(1/2)^2]
PWLW/2 = PWLW - 6
When two half-streams with PWLW/2 are mixed, the resultant PWL of two half-streams may be estimated base on method as discussed in "Calculate Combined Sound Power Level (PWL)".
From this post,
Both half-streams have same PWL. The PWL difference (PWL,diff) is zero (0).
PWL adder = 10 ^ (0.4771 - 0.0795 x PWL,diff)
PWL adder = 10 ^ (0.4771 - 0.0795 x 0)
PWL adder = 3 dB
Both half-streams have same PWL.
Maximum PWL = PWLW/2 = PWLW - 6
Therefore, Combined PWL is :
Combined PWL = PWLW/2 - PWL adder
Combined PWL = PWLW - 6 - 3
Combined PWL = PWLW - 3
So, half the flow will results approximately 3 dB reduction from total flow.
Ref.
i) "Designing Piping Systems Against Acoustically Induced Structural Fatigue", E.L. Eisinger, Journal of Pressure Vessel Technology, Aug 1997.
Related Topic
Above equation will provide PWLW for a stream with W mass flow. If the stream is split into two stream, the mass flow will be W/2.
Sound Power level for single half-stream (W/2),
PWLW/2 = PWLW + 10Log [(1/2)^2]
PWLW/2 = PWLW - 6
When two half-streams with PWLW/2 are mixed, the resultant PWL of two half-streams may be estimated base on method as discussed in "Calculate Combined Sound Power Level (PWL)".
From this post,
Combined PWL = Maximum PWL + PWL Adder
Both half-streams have same PWL. The PWL difference (PWL,diff) is zero (0).
PWL adder = 10 ^ (0.4771 - 0.0795 x PWL,diff)
PWL adder = 10 ^ (0.4771 - 0.0795 x 0)
PWL adder = 3 dB
Both half-streams have same PWL.
Maximum PWL = PWLW/2 = PWLW - 6
Therefore, Combined PWL is :
Combined PWL = PWLW/2 - PWL adder
Combined PWL = PWLW - 6 - 3
Combined PWL = PWLW - 3
So, half the flow will results approximately 3 dB reduction from total flow.
Ref.
i) "Designing Piping Systems Against Acoustically Induced Structural Fatigue", E.L. Eisinger, Journal of Pressure Vessel Technology, Aug 1997.
Related Topic
- Calculate Combined Sound Power Level (PWL)
- Measures & Technique In Eliminating / Minimizing PWL
- Principle in Eliminating & Minimizing AIV Impact
- Energy Input or E-method In Assessing AIV
- Assess AIV with "D/t-method" with Polynomial PWL Limit Line
- Assess AIV with "D/t-method" with Logarithm PWL Limit Line
posted by Webworm, 6:17 AM
2 Comments:
Hi,
Could you please share the references you have used for your study on AIV and PWL prediction?
Included in the post.
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