PWL Reduction By Splitting Flow

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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 :

Refer to "Sound Power Level (PWL) Prediction from AIV Aspect" for more discussion on above equatio.

Above equation will provide PWL_W 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),

PWL_W/2 = PWL_W + 10Log [(1/2)^2]
PWL_W/2 = PWL_W - 6

When two half-streams with PWL_W/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 = PWL_W/2 = PWL_W - 6

Therefore, Combined PWL is :
Combined PWL = PWL_W/2 - PWL adder
Combined PWL = PWL_W - 6 - 3
Combined PWL = PWL_W - 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