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Louvers Face velocity and open area calculationHelpful Member!(3) 

SandmanR (Mechanical) (OP)
11 Feb 11 13:23
I am working on the design of an air intake house for a certain capacity of air flow. Now this was designed by a consultant with a lot of experience several years ago. Now we are replicating this design for the intake housing based on the concept of Inertial separators.
I am trying to understand how to calculate the fave velocity through the louvers into the Intake housing and also calculate the pressure drop across the system.
If anyone can guide me here, i can give more details on the dimensions of the said intake system.

Thanks,
Helpful Member!  imok2 (Mechanical)
11 Feb 11 17:34
The basic considerations for selecting louvers are Free Area, Water Penetration, and Resistance to Airflow (Pressure Loss). Once these concepts are understood, they can be used to properly apply a louver.GO here: http://www.archlouvers.com/How_Louvers_Work.htm
Helpful Member!(2)  berkshire (Aeronautics)
11 Feb 11 21:39
You also mention inertial separators, are these incorporated right into the louver, or are they in the duct behind the louver.

 The requirements for the separator are diametrically opposed to that of the louver.
  An inertial separator requires high velocity air to throw the dust particles out of the airstreams.
Louvers prefer the air velocity to be somewhat lower.
B.E.
SandmanR (Mechanical) (OP)
14 Feb 11 10:59
Thank you Imok2.
Thank you Berkshire, however now i am confused.
This is an inertial separator application.i am attaching some drawings that we have devised for fabrication. The volume of air-flow handled by the Intake house is going to be 248,000 CFM of which 10% is bleed air. the air enters through the inertial separators on either side of the filter house (please see attachments for clarity).
I would like to understand how to calculate the face velocity and thereby try and determine the pressure drop across the filter house.

Thanks much.
SVR
berkshire (Aeronautics)
14 Feb 11 15:24
Sandman
Your attachments did not come through.
 However most inertial separators work by getting the air to rapidly change direction, throwing the particles into a calm area where they can settle and be collected, these work best with coarser particles.
You now mention a filter house. So without seeing your drawings I am envisioning a Louver on a case or box with the separators and filters inside it.
 If that is so the louver should be treated as a separate calculation from the filters.
That is size the louver for free area, lowest pressure drop Etc.,
Based on the air requirements for the filters.

If the louvers themselves are also inertial separators then the velocity of the louver has to be high enough to throw the particles out of the air stream.
Here is a link to a dynavane air separator http://www.camfilfarr.com/Global/Documents/US/Literature%20Library/Dynavane%20Inertial%20Separator%20Product%20Sheet.PDF

B.E.
SandmanR (Mechanical) (OP)
15 Feb 11 12:35
Berkshire,
Thank you so much for your response.
The example that you have sent is exactly what our design is based on; the Dynavane type inertial separator. I am going to attempt to upload an attachment with my design drawings for this application.
Based on Imok's recommended websites, i have managed to calculate the total free area for the entire Inertial separator unit and thus the face velocity.
My results are as follows(please correct me if you think I might be wrong here):
the minimum gap between the louvers is 0.14" and the length of each louver is 3.875". So the total free area for each separator will be 0.14 x 3.875 x 55(number of gaps, between 56 louvers) x 17(columns of louvers) x 2(for two sides) = 7.046 sq.ft.
Now for the entire system, free area will be 7.046 x 28 (14 on each side) = 197.29 sq.ft.
The total volume of inlet air is 248,000 cfm (including bleed air)
Thus, the face velocity comes to be 248000/197.29 = 1257 fpm
Now, applying the Darcy-Weisbach Equation to calculate pressure drop; Δp = f (l / d)x(ρ v2 / 2).
HERE, I AM NOT SURE WHAT FRICTION COEFFICIENT TO CONSIDER. ALSO, IS IT SAFE TO ASSUME l/d to be 1 since its a duct almost square in shape? I am pretty sure, it should be turbulent flow.

I am hoping i am pretty close to the solution, please advise.

Thanks in advance.

Sandman
 
berkshire (Aeronautics)
16 Feb 11 1:32
Sandman R
This may help you from the engineering tool box.http://www.engineeringtoolbox.com/ductwork-friction-loss-d_1122.html
  I am a little unclear what you are trying to calcuate, are you calculating a straight flow deltaP1, or are you calculating the flow at its moment of reversal from the filter where the turbulence and drag are greatest delta Pd ?
B.E.
 
SandmanR (Mechanical) (OP)
16 Feb 11 12:52
Berkshire,

Thank you for your response.
I am primarily trying to calculate the pressure drop across the intake house before entering the silencer section.The velocity that i have calculated is i believe the face velocity at the exit of the inertial separator through the louvers.
Since, we are building the Intake housing, i am trying to calculate the pressure drop across our system using this velocity.
The attachment I had uploaded illustrates the design of the Inertial separator.
The Intake housing is 12' wide x 22 ft deep x 12 ft high.

Thanks,

Sandman

 
berkshire (Aeronautics)
16 Feb 11 14:18
Sandman,
On the information from Dynavane that I linked you to, there is a pressure drop chart, " Clean Airflow per Single Cell", on page 4.
you can use this to cross check your calculations.
   Since you are using the information gleaned here, to reverse engineer a competitors product, I do not feel comfortable helping you further.
B.E.
SandmanR (Mechanical) (OP)
16 Feb 11 14:41
Berkshire,

This product was designed and engineered by a consultant that was hired about 10 years ago. However, the individual in context is passed away a few years ago and I am trying to understand and deduce his calculated information and design criteria.
During my research on inertial separators and exploring the different products out there, i came to the understanding that the Dynavane type separator is similar in nature to the design formulated by the consultant, however, not the same since dynavane uses individual cells comprising of a whole block of a unit put together for different applications based on the capacity required, and ours has been custom designed for this particular application.
The deduction i came up with regarding the comparison to Dynavane type of separators is completely based on my observation and basic understanding of inertial separators.

Hope this clears things out some.

Regards,

Sandman

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