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Volume of an Elbow Duct

10/22/2015 2:42 AM

Can anyone help me out how to find the volume of an Elbow Duct??

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#1

Re: Volume of a elbow duct

10/22/2015 2:53 AM

Cross sectional area multiplied by length along the centreline must be a reasonable approximation for all practical purposes..

This begs the question why does it matter, what type of duct, what sort of accuracy are you after and what is your shoe size?

Del

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#2
In reply to #1

Re: Volume of a elbow duct

10/22/2015 3:00 AM

I guess the guy needs the lateral area of the elbow duct for QA purposes. Unless otherwise, he plans to hydrotest ducts? --hmmm

Then you can have his shoe size

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#12
In reply to #2

Re: Volume of a elbow duct

10/24/2015 7:35 AM

You are not an engineer. Maybe you could be someday. There is a reason we have two ears and one mouth.

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#3

Re: Volume of a elbow duct

10/22/2015 3:33 AM

See here!

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#4

Re: Volume of a elbow duct

10/22/2015 3:53 AM

It still smacks of huge overthink and looking for unnecessary accuracy.

If it's a rectangular duct, just measure half way across at regular intervals and mark dots, run a tape measure round the curve through all the dots and read off the length.

Multiply that by the cross sectional area of one end. Or if you want more accuracy. Measure the width to check if it is constant round the curve, it it's not, then measure at regular intervals and average it to give an average cross sectional area.

I can't see how the accuracy will be any less than some fancy formula that relies on you estimating a bend radius anyway.

Del

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#5

Re: Volume of an Elbow Duct

10/22/2015 9:15 AM

Close off one end with plastic film, tape, whatever. Then fill the elbow with water.

Measure the amount of water, then determine the volume of the elbow with a conversion. (E.g., 1 US quart = 57.75 cubic inches.)

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#6

Re: Volume of an Elbow Duct

10/22/2015 3:06 PM

Yes. Usbport just did.

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#7

Re: Volume of an Elbow Duct

10/22/2015 5:48 PM

(Cross-sectional area) x (arc length of center-line radius). A local high-school geometry student could probably assist with this.

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#8

Re: Volume of an Elbow Duct

10/22/2015 5:54 PM

Where are all my Del's GAs you bunch of tightwads?

Kris

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#9
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Re: Volume of an Elbow Duct

10/22/2015 6:07 PM

My crappy browser of the moment does not register GA or OT votes, nor does it have any text effects or link insertions in the reply window. The best I can offer is a rain check.

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#10

Re: Volume of an Elbow Duct

10/23/2015 11:09 AM

Curved pipes in the shape of circular arcs are frequently used in plumbing. To find the capacity of a pipe arc, you can consider the pipe as a section of a torus, and then use the formula for toric volume. When figuring volume of a curved pipe, you must know the outer diameter, thickness, band angle, and either the bend radius OR bend distance. See figure below:

Recall that if a torus has a diameter of X and a hole diameter of Y, then the equation for its volume is
Torus Volume = (π2/4)[(X/2)2 - (Y/2)2](X/2 - Y/2)
For a torus sector with an angle measure of θ┬░, multiply the torus volume by a factor of θ/360. For example, if you have a 90┬░ section of torus, the volume is multiplied by 90/360 or 1/4.
In the case of a curved pipe, we consider the interior of the pipe to be a torus section. If the pipe's width is c, the wall thickness w, and the bend radius r, then the torus diameter X and hole diameter Y are given by the equations
X = 2c - 2w + 2r, or
X/2 = c - w + r
Y = 2r + 2w, or
Y/2 = r + w
Putting all of the pieces together, you get the volume formula for a curved pipe:
Pipe Volume = (π2/4)((c-w+r)2 - (r+w)2)(c-2w)(θ/360).

The volume by weighing method is probably accurate enough for most applications but that method requires you to have the elbow to seal it and weigh its contents. The above formulas allow you to make the calculations without having the elbow.

Good Luck, Old Salt

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#13
In reply to #10

Re: Volume of an Elbow Duct

10/24/2015 1:14 PM
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#11

Re: Volume of an Elbow Duct

10/23/2015 7:16 PM

Use a dB meter to measure volume.

There's a phart smone app for it.

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Users who posted comments:

Anonymous Poster (1); Del the cat (2); IdeaSmith (1); Legolaz (1); lyn (1); Mikerho (1); old salt (2); PWSlack (1); Tornado (2); Usbport (1)

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