funnel size and shape

volkanokaren · #1 2012-08-20, 8:46am

Good morning,I have been researching thanks to the help on LE and
artglassanswers.I am having the funnel for my ventilation made and using hard pipe with a vortex inline fan.My ? is if I have a 6 inch duct should i be using a 12 inch funnel.Also after reading Dale's article Ventilation for dummies in artglassanswers I'm kind of leaning towards a round funnel instead of square.

I would love to hear your thoughts.

Karen
Volkano Exotik

ripzz

JoeDeM · #2 2012-08-20, 10:42am

Quote:

Originally Posted by volkanokaren

Good morning,I have been researching thanks to the help on LE and
artglassanswers.I am having the funnel for my ventilation made and using hard pipe with a vortex inline fan.My ? is if I have a 6 inch duct should i be using a 12 inch funnel.Also after reading Dale's article Ventilation for dummies in artglassanswers I'm kind of leaning towards a round funnel instead of square.

I would love to hear your thoughts.

Karen
Volkano Exotik

ripzz

I would go with round over square, 12" should be fine. If you are having it made I would ask about having a safety edge or rolled edge done on the 12" end, less chance of getting cut if you accidentally bumping it. one thing to remember is to not have your torch too far away from the funnel, and if at all possible I would place the funnel so that it's inline with the torch, that way you get the Maximum Capture.

volkanokaren · #3 2012-08-20, 12:04pm

Thanks for the reply.I am going to get my duct today,they are making the
funnel as well.It's getting closer.

Karen
Volkano Exotik

ripzz

cheng076 · #4 2012-08-21, 11:23am

Rolled edge is good idea and you can always squeeze the funnel side in a bit to get a more rectangular shape if needed. I would have gone with a bit bigger funnel; probably 18". but I aint there to see the setup. Take care.

volkanokaren · #5 2012-08-21, 12:21pm

I agree with the rolled edge.My set up includes 6inch 452 cfm vortex fan w/speed control,
2 90's,36 inch all b vent 6inch pipe and of course the funnel in front of me.
I was wondering if I could go a little bigger with the funnel without comprimising air flow.

Karen
Volkano Exotik

ripzz

Dale M. · #6 2012-08-21, 4:14pm

Bigger may be better... More capture area the safer the studio...

Dale

volkanokaren · #7 2012-08-21, 6:11pm

Thanks Dale,yes bigger sounds better....but of course the ? by how much.
My brain kinda hurts,a lot of thought and research has gone into this.Safety is #1
$ is second.It would be great to nail this on the first try.I pick up my ducting in two days so hopefully I will have picked a # by then.
Thoughts are appreciated.

Karen
Volkano Exotik

ripzz

JoeDeM · #8 2012-08-22, 6:38am

You can't go wrong with bigger, get a quote for 16" or 18". 16" will give you a 324cfm per foot of opening, and 18" will give you 257cfm per foot of opening.

Some info
There are 3 thing to consider when designing a funnel CFM, SIZE, and DISTANCE. The Capture efficiency is directly related to the size and distance. Maximum efficiency is achieved at the threshold of the opening, at this point we get 100% efficiency, as we move farther back from the opening that capture efficiency drops. So using your numbers and measuring roughly from the end of the flame, I'm using 6" for this example.

452cfm 12"size 6"dist = 23.90% and 152fpm
452cfm 16"size 6"dist = 35.82% and 128fpm
452cfm 18"size 6"dist = 41.40% and 117fpm
452cfm 20"size 6"dist = 46.59% and 107fpm

The Numbers are for Static air, so they will actually be better with the torch helping to push hot gases into the opening, but they give us a frame of reference for discussion. The CFM will only effect the fpm (feet per minute).

volkanokaren · #9 2012-08-22, 2:13pm

Ohhhhh.Thanks JoeDem.Lets see if I am understanding this correctly.
The wider the funnel the more efficient the system will be as long as the distance of the
flame is not pulled back from the opening.? where should the tip of the flame be?
Another ? that has come to mind now is the depth of the funnel.What dictates that for efficiency?
You peeps are the best,thanks so much.

Karen
Volkano Exotik

ripzz

JoeDeM · #10 2012-08-23, 1:02pm

Quote:

Originally Posted by volkanokaren

Ohhhhh.Thanks JoeDem.Lets see if I am understanding this correctly.
The wider the funnel the more efficient the system will be as long as the distance of the
flame is not pulled back from the opening.? where should the tip of the flame be?
Another ? that has come to mind now is the depth of the funnel.What dictates that for efficiency?
You peeps are the best,thanks so much.

Karen
Volkano Exotik

ripzz

The depth of the funnel has no effect, the distance is from the end of the flame, or you can measure from the torch face 12" to 14". There is a trade off of going too wide your FPM drops & your CFM gets spread across the face opening which you want to keep high.

452 @ 16" gives you 322cfm per foot of opening
452 @ 18" gives you 255cfm per foot of opening
452 @ 20" gives you 215cfm per foot of opening

Also it hasn't been mentioned but have you thought about make up air, Dale has a good illustration showing make air using a short circuit approach, were the make up air is ducted to the bench.

volkanokaren · #11 2012-08-24, 8:36am

Hi JoeDeM.Thanks for this info,I'm leaning towards 15 or 16 inch for the exact reasons you have you have stated and shown here.Hopefully it works.
I do have make up air coming from behind me through the bottom half of my dutch door.If it is not sufficient or if it's too cold I was going to put a 6inch duct through the wall behind me.Having said that I will check out Dale's info again today.My room is 8x8.
Do you think that is a good choice?
I would post pics here but I find it very difficult to load pics on LE,sometimes it works but
more not.
I'm so close to melting glass again I can feel it.

Karen
Volkano Exotik

ripzz