chimney flow rate calculator

[brokencookie]

This calculation was just too good to pass up. I have attached a excel spreadsheet that will calculate your chimney flow. I protected the sheet just so you cannot accidently erase the formulas. There is no password on it if you want to modify. I also included temperature and measurement conversions for the metric challenged. Just input your data and see if it makes a difference. I would be really interested to have a few people with completed ovens provide some real data about flow rates and how well their oven draws.


Bruce

[Frances]

Re: chimney flow rate calculator

oohkaay....

mine equals 70418.4...
that would be m3/s, right?

Its really cool. I love it, really! ....but what does it mean??

[brokencookie]

Re: chimney flow rate calculator

Frances
I think you input your chimney height in centimeters, my error there. All measurements are in cm except for the chimney height with should be in meters. If you change the value you will probably end up with a number less than 1000.
My thought was that people could report of the actual value for thier working WFO and an opinion as to if their oven drew well. Then builders could preplan chimney diameter and height. We should be able to work up a minimum number for good draw.
Hopefully members reporting would include the data on chimney size. The temperature information is fun but not as useful for our purposes.
I have attached a new spreadsheet because I forgot to leave a few cells unlocked

Bruce

[Wiley]

Re: chimney flow rate calculator

Bruce, cool calculator. Now I hope people will give some data of ovens that draw well.

A question regarding the calculated data and reality: If a height of door to oven ceiling height is wrong and as a consequence the oven is choked for want of air (doorway too short) or too high causing the heat to excape too quickly the temp difference may be the same but the actual draft may not be as efficient right? So it might be good if people reporting their data also state the ratio of door height to ceiling height and whether their WFO is dome or barrel?

Just trying to help improve the returned data.

Wiley

[jengineer]

Re: chimney flow rate calculator

mm = millimeters
cm = centimeters
conversion from C to K is C +273.15

You sure coefficient is correct? most chimney are more like the photo...The effective coefficient of discharge for flow nozzles in pipelines varies from 0.96 to 1.2 for turbulent flow and increases as the throat-to-pipe-diameter ratio increases. C in our systems will vary due to some folks using angle brackets and others making a smoother trend.

[gjbingham]

Re: chimney flow rate calculator

Bruce,
I thought your degree was in music theory? My god man, what the heck is all this?? Are you goofing off at work??

[brokencookie]

Re: chimney flow rate calculator

mm = millimeters
cm = centimeters
conversion from C to K is C +273.15

You sure coefficient is correct? most chimney are more like the photo...The effective coefficient of discharge for flow nozzles in pipelines varies from 0.96 to 1.2 for turbulent flow and increases as the throat-to-pipe-diameter ratio increases. C in our systems will vary due to some folks using angle brackets and others making a smoother trend.

I knew I could find an engineer on the forum. I am just the guy who bubble gums these things together. Kind of a close enough approach for our purposes. I used 273 as the conversion to K and built it into the worksheet as most of the builders work in degrees C . I used 0.7 as the coefficient based on the information I had on hand. I figured that even if the modeling was not exact it could prove to be a useful preditive tool for oven builders. For example, I found that the difference between a 6 inch and an 8 inch round flue pipe is that an 8 inch has almost double the draw for the same height.
Please feel free to correct and repost. The worksheet was intended as a starting point, not a finished product.

Engineers !!!!

ON YOUR MARK

GET SET


CALCULATE !!!

[brokencookie]

Re: chimney flow rate calculator

Bruce,
I thought your degree was in music theory? My god man, what the heck is all this?? Are you goofing off at work??

George
Music theory is the science of music. Compostion is the art. My degree is music theory and compostion. I am the scientific artist That also makes me smarter than most musicians so I went out and got a job I could make a living at.
Yes, I am goofing off at work. I have my crew so well trained that they only need me for unusual things and some paperwork. I amuse myself by creating automated programing that further reduces my work load. Since I am management, I am not allowed to do real work, the union would have a tizzy.
So my job is to watch other people work, Find ways to reduce my own work, and stay out of trouble (like that's really going to work)

Bruce

[jengineer]

Re: chimney flow rate calculator

Don't bait the engineer - he might get hooked

[brokencookie]

Re: chimney flow rate calculator

Don't bait the engineer - he might get hooked

Sorry, I have a bunch of engineers where I work. I have the task of providing data to them and then listening to them tell me the data "must be wrong" since it did not match their models. I did not mean to step on toes.
I am serious about improving the spreadsheet though. If we can get good data that will help other builders then its all good. Besides, even engineers have to have a hobby. They must be the builders with 10 thermocouples built in. ( baiting intentional this time )


Bruce

[gjbingham]

Re: chimney flow rate calculator

Scary stuff Bruce! Someone who really (really) understands music is as wierd as finding someone who understands cosmology (no, not cosmetology!). I don't even want to hear about the math. I get lost every time.

Somehow, I knew you were goofin' at work! I'm calling big oil!

[jengineer]

Re: chimney flow rate calculator

Ok I will take the bait but drop it off on a smoke and mirrors expert.

[christo]

Re: chimney flow rate calculator

I'm using 8x8 tile with a 8x14 inch transistion also made from tile
(design stolen with pride from DMUN)

I get a 923 - when I include the height of the transision plus the length of one tile.

My oven draws well. I have not had to clean any soot off of the front facing bricks ... knock wood.

Christo

[brokencookie]

Re: chimney flow rate calculator

Great, we have our first baseline number. 923 draws well. Anyone have a chimney with a lower numer that draws well ?

[wlively]

Re: chimney flow rate calculator

I have an 8 inch duravent 18 inches high above my custom poured vent transiton, which approx 8 inches high. Just using those numbers I get 684 if I read the comments about using cm istead of mm correctly.

My chimney draws well.

Although this baseline number does not include the effect a good transition has for increasing the velocity of the air flow.