Flow Rate Calculations 1

[MeEn]

Hi guys,

I am new engineer how is working on replacing Fume Hood inside a lab with a new one.

I would like to know how to do the required flow rate so that I will select the blower accordingly. We are shooting for 100 f/min velocity through the face of the hood. I also I would like to know how to find the total static pressure.

The duct diameter is 10 inches.
Please advise me
Thank you very much

 

[svanels]

These calculations are valid for a canopy type fume hood


Flow through hood

Q[sub]2[/sub] = 1.4 * P * D * V {cfm}

where

P = perimeter of tank or table below the hood {ft}
V = capture velocity (100 - 150 fpm)
D = free space above tank or table {ft}

When the hood is above a hot area, an additional flow Q[sub]1[/sub] of air or vapors is

formed.

To remove the vapours it is necessary that Q[sub]2[/sub] > Q[sub]1[/sub]

For practical values Q[sub]2[/sub] = 1.2 * Q[sub]1[/sub]

Calculation of Q[sub]1[/sub]

Valid for D <= 3 ft

1) Hood above hot area without vapor generation


Q[sub]1[/sub]= 5.4 * S * \[sup]3[/sup]/[sup]--[/sup]( h * dt[sup]1.25[/sup]) {cfm}

S = Area hot plate { ft[sup]2[/sup]}
t = temperature difference hot plate and ambient air {[sup]o[/sup]F}
h = heigth hot plate above the floor {ft}


2) Hood above tank with hot liquid (vapor generation)


Q[sub]1[/sub]= 290 * S * \[sup]3[/sup]/[sup]--[/sup]( h * G) {cfm}

S = Area top side of tank { ft[sup]2[/sup]}
G = Vapor formation {lb/ft[sup]2[/sup]/min}
h = heigth tank with hot liquid {ft}


Regards
Steven van Els
SAvanEls@cq-link.sr

 

hi there
i am constructing a natural drain here on my farm
the top of the drain is 12 ft wide
width of bottom is 2.7ft
gradient{fall} 420
depth of drain is 5 ft

can someon eplease calculate the flows in GPM when the water depth is 2ft,3ft,4ft

regards and awaiting a reply

John Lochhead
email is jlochhead@fencepost.com

 

[waynef]

John,

You should start your own thread. In it you should also state the length of the channel you are constructing as well as whether it will be concrete, grass, gravel, dirt, etc.

I'm assuming that the depth you are concerned with is the depth at the very beginning of the channel (drain). If you supply the additional data I've described, the flow at the end of the drain can be calculated.

I'm also assuming that the dimensions (width, depth)of the drain are uniform from beginning to end.

Wayne

 

[bbsmag]

Checkout

http://virtualdesignbuild.com/DB/equip/ductwork.htm

for some information.

 

[Thom2]

Greetins MeEn,

I would like to suggest to you that you provide plenty of isolation valves and locations for low point drains when you do have to isolate sections of piping. An old Maintenance Plumber told me that the first time you use a valve the valve has paid for itself.

Trying to plan for the future is almost impossible...... but something you might be able to do is this: Contact the people who will be actually using and maintaining the system... ask them where they would like valves / drains / filters / room for access or maintenance.....

You are very fortunate to have this opportunity to design this system and it sounds like you are working hard to make it a good one !

Good luck,

 

[parcorian]

what are the steps to design piping for refinery