Axial Fan Air Volumes

[chillman]

Hi everyone,

I really need some technical help.
I've had the same problem for over a year now,
I've searched for answers time and time again with no ending.
I'm doing my refrigeration mechanic apprenticeship but I currently have a job at a manufacturer of small fin-tube heat exchangers. I'm really learning alot and I am interested in learning alot more
My problem concerns air volumes of axial fans.
Each fan has its volume/pressure chart supplied by the manufacturer.
My problem is i need to calculate the air volume in meters cubed per second using a specific fan on a specific coil.
I've heard a couple right ways of achieving my goal. One using a simple anemometer and a simple formula.. another working off the pressure drop of the coil... and others that dont make sense at all.

Please Could anyone with answers help me ?

[nike123]

Stick with using a simple anemometer and a simple formula. That is only way to tell you actual air volume.
Calculating from catalog data and presumed (or calculated) pressure drop couldn't tell you actual volume, only can tell you what it should be.

[Samarjit Sen]

Using an anemometer and a simple formula is the best and more accurate way to find the Air Volume.

[US Iceman]

I think we should also suggest the use of multiple readings with the anemometer (over the face of the coil). The are velocity vectors across the face of the coil, therefore a single reading will not provide sufficiently accurate data for the calculations.;)

[Samarjit Sen]

Yes US Iceman,

It is always better to take multiple readings over the face of the coils. I feel this way one can get a very precise result.

[nike123]

This is how it is suppose to do that:

http://farm3.static.flickr.com/2136/2226730204_82eb117903_b_d.jpg
(http://farm3.static.flickr.com/2136/2226730204_82eb117903_b_d.jpg)

[Brian_UK]

Thank you Nike I was going to say the the best way of performing tests and acquiring reliable data is to create a test bed.

Use a suitable length of ducting connected to the inlet of your test fan which, in turn is connected to your coil.

You can then use a pitot-static tube and manometer to accurately measure the airflow. Anemometers will give you different readings depending on whether it is measuring the inlet or the outlet side of a device due to the possible jetting effect on the outlet side.

[Samarjit Sen]

Hi Nike123, could you please give us the reference to the details provided by you as I would like to download the complete thing and study it. It is of interest to me. Thanks.

[US Iceman]

Brian, you bring up a good point. Here in the US we have an organization that specifies the conditions under which the fan air volume is determined (I'm sure you guys have a comparable scheme there).

If the conditions imposed by the fan location or installation affect the fan performance then you have to correct this by the system effect factors also.

In most cases, if I'm not mistaken the fan volumes listed by the fan performance curves are for free discharge only unless otherwise stated.

Nike123, your post on the picture is exactly what I was thinking of. Thank you for posting this.

[nike123]

Hi Nike123, could you please give us the reference to the details provided by you as I would like to download the complete thing and study it. It is of interest to me. Thanks.
I found that at www.omega.com as two page broshure for some instruments. Second page is just instrument presentation. I have somewhere e-book with this so when i find her i will post it here.

[chillman]

Thanks everyone for their input!!

Ya i was going to use an anemometer and simple take muntiple measurements and work from the average..
But there is such a huge variation of air velocity in each position of the coil..

I've also looked at instruments and Ive seen ones that really have accurate Volume measurement using capture hoods but they are for measuring outlets of HVAC ducts and not really designed for what i need..

I really am interested in building up a testing rig..
Another problem is the sizes of my fans which range from 250dia to 500dia, and then even bigger 800dia fans..
They are all suction fans and pull the air through the fins and out the cowling..
If i could perhaps come up with a setup where i attach a jig with all the instrumentation to the coil casing but i'm honestly in the deepend on how to do that..
Thank you to nike123 for that information page.
I think if i place a ducting over the fan and take the measurements on the points indicated would be a good way of getting the average flow.

Does anyone know how the manufacturers do it,
I know certain places do testing for customers but at a huge cost per unit, I'm confident if I knew exactly how they calculated theirs I could do a sufficient job myself.

[Samarjit Sen]

Thank you nike123. I shall be keenly awaiting the link to the e book. I am very much interested to know more about Air and its effect.

[nike123]

Thank you nike123. I shall be keenly awaiting the link to the e book. I am very much interested to know more about Air and its effect.

This is one for beginning. I am little unorganized (as all great minds :D) so, it is going to take a wile until I dig right one.;)

http://www.mediafire.com/?1xozjxtyuka

[nike123]

Moderators, is this against rules?:confused:

[Samarjit Sen]

Thank you nike123. I can wait.

[US Iceman]

nike123,

I believe you can post these links if they are publicly available on the internet. By that I mean free-of-charge from the provider and not a pirated source.

I will check with the boss of RE for his input also.

[Brian_UK]

Here's how some of the big boys do it......

http://www.fire.nist.gov/bfrlpubs/build03/PDF/b03081.pdf

[chillman]

Wow thanks Nike and Brian.. thats the stuff I crave!
You can never know too much!!
I really appreciate your posts..
You can google for weeks and not be able to find such an informative pdf.. and with 384 pages in it :)

[chillman]

I know a guy that writes articles for our refrigeration and airconditioning magazines. I bought a book from him. It has a nice practical way of explaining refrigeration if anyone is interested.
I know its not free but its worth keeping an eye on his site ..
alder.com

[nike123]

This is one for beginning. I am little unorganized (as all great minds :D) so, it is going to take a wile until I dig right one.;)

http://www.mediafire.com/?1xozjxtyuka


This is another:
http://www.mediafire.com/?6dtbwnrkndm

[nike123]

This is one for beginning. I am little unorganized (as all great minds :D) so, it is going to take a wile until I dig right one.;)

http://www.mediafire.com/?1xozjxtyuka

More:
http://www.mediafire.com/?2fysmnxtr24

[nike123]

This is one for beginning. I am little unorganized (as all great minds :D) so, it is going to take a wile until I dig right one.;)

http://www.mediafire.com/?1xozjxtyuka

This is one you are looking for (i think):

http://www.mediafire.com/?cnwvt4ftona

[HVACGod]

Thought I'd give you another available text to consider Chill, not that you've not been given enough already. This particular copy is protected by password requirement to our Technical Archives, but I am certain there are other sources on the net for the text, I didn't search since I already knew the path to this copy. Excellent text for anyone involved with blowers, fans and airflow issues.

Title of this text is the Loren Cook Engineering Fan Cookbook [Basics | Design | Formulas | Laws]:
http://www.hvacprotech.org/toc/Duct%20&%20Airflow/Lorencook%20fans%20cookbook.pdf

Note to the Mods: If this link is not permitted, please remove. Access is limited to verified trade professionals only and requires a password to access, but at no cost.

[US Iceman]

I know a guy that writes articles for our refrigeration and airconditioning magazines. I bought a book from him. It has a nice practical way of explaining refrigeration if anyone is interested.
I know its not free but its worth keeping an eye on his site ..
alder.com


Geoff's book and set of articles are well worth the investment. He has a unique way of writing his articles that clearly make sense and help the reader to understand the problem or issue.

Here is a link to his site: http://www.alder.co.za/

[SteinarN]

One method i have used is to place an electrical resistive heater in the inlet airflow. Its easy to measure the power by taking the voltage x the amperage. Its important to make sure that all the warm air is drawn into the inlet. Then measure the temperatur difference between the entering air and the fan outlet where the air hopfully is thorougly mixed.


m3/s=heaterpowerx1,2
temperaturdifference

[Josip]

Hi, all :)



Title of this text is the Loren Cook Engineering Fan Cookbook [Basics | Design | Formulas | Laws]:
http://www.hvacprotech.org/toc/Duct%20&%20Airflow/Lorencook%20fans%20cookbook.pdf

Note to the Mods: If this link is not permitted, please remove. Access is limited to verified trade professionals only and requires a password to access, but at no cost.

or here: without password;)

http://www.lorencook.com/PDFs/cookbook.pdf

Best regards, Josip :)

[chillman]

havent been around lately, glad to see the information keeps coming regardless..
I'm really interested in using temperature difference at heaters,
how exactly does this work, if you dont mind answering.

I've been doing a little investigating using the information from this site and things i've been told from other guys in the business,
I made a grid of hollow 3/8" copper pipe to fit nicely into the cavity between the core and my fan cowl,
I plan to dril little holes alone the lengths of the intersecting pipes and connect an exit to an aneometer, i think this should give a good average pressure from the fan, similiar to how some of the duct instruments work, i met a national manager of a fan manufacturer and he assured me that they take the average pressure at points around the cavity and the average pressure relates to airvolume of the pressure / volume chart for that fan.. so i thought it myt be interesting to see wat happens if i have a grid pattern with multiple points linked to the same outlet

[frank]

I made a grid of hollow 3/8" copper pipe to fit nicely into the cavity between the core and my fan cowl,
I plan to dril little holes alone the lengths of the intersecting pipes and connect an exit to an aneometer, i think this should give a good average pressure from the fan, similiar to how some of the duct instruments work, i met a national manager of a fan manufacturer and he assured me that they take the average pressure at points around the cavity and the average pressure relates to airvolume of the pressure / volume chart for that fan.. so i thought it myt be interesting to see wat happens if i have a grid pattern with multiple points linked to the same outlet

That's called a Wilson Flow Grid http://www.airflowinstruments.com/products/detail.aspx?Cid=9&Pid=40