×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Perforated plate pressure drop calculations?

Perforated plate pressure drop calculations?

Perforated plate pressure drop calculations?

(OP)
I'm trying to figure out how to calculate the pressure drop of a perforated plate!
Could you provide me with assistance or information?

My current project is the design of a biotrickling scrubber.  It is essentially a biological scrubber using lava rock with nutrient rich solution to degrade foul air (predominantly hydrogen sulfide).

The tower I'm designing is about 22 feet in diameter and the lava rock packing is 12 feet high.  The flow rate is approximately 20,000 scfm.  In order to insure that the foul air is distributed evenly across the bottom of the lava rock packing, I'm planning to install a perforated pvc plate beneath the lava rock packing.  The rule of thumb to create an even air distribution is to create a 1inch w.c. pressure drop across the perforated plate.  This would in effect create a back pressure.

Do you know what formula I could use to calculate the pressure drop?  The surface area of the plate is fixed, but I'll have to vary the number and diameter of the holes on the plate.

RE: Perforated plate pressure drop calculations?

See ASHRAE Applications, Ch. 51, Eqn. 9. This is from the orifice equation with conversion factors and built-ins to simplify:

Q = 2610 * A * (dP)^.5

Q is flow in cfm, A is area in ft2, dP is in inches w.c.

So my guess is 7.66 square feet net (total open area of all your holes). If this works out for you, please re-post as I'd be interested to know! Good luck, -Chas

RE: Perforated plate pressure drop calculations?

(OP)
using that formula, the ratio of passage area to total area is 7.66/379.94 = 0.02.  So the holes cover about 2% of the total area...  it doesn't seem like much of an opening..  I'll have to double check.,

RE: Perforated plate pressure drop calculations?

The following link from the Industrial Perforator's Association should be exactly what you are looking for.

http://www.iperf.org/pressure.htm

RE: Perforated plate pressure drop calculations?

I agree it sounds small, but this could be because your face velocity for 20,000 cfm across 380 square feet is only 53 feet per minute. I can burp faster than that. I stand by my verdict! (look, it's alot easier to add holes later than to try to remove them...)

RE: Perforated plate pressure drop calculations?

Dear brazilianjj:

Please also consider the mass tranfer for this problem.  Further, the L/D ratio you propose will make distribution of lean solvent difficult.  If pressure drop is the critical economic parameter and you must have such an odd shape commercial vessel, you will be plowing some very difficult ground for design of the liquid distributor at the top of this vessel. It will require likely a sealed chimney tray with both chimneys and tray perferations.  You have a tough problem.

RE: Perforated plate pressure drop calculations?

There is a great shareware program called Engineering Power Tools.  You can search the net on sites such as C/Net or ZDNet.  It has an area in the Mechanical tools which will calculate PD through a perf plate.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources