Stack temperature and smoke velocity

[Swedishchef]

Hey guys

Has anyone ever measured smoke velocity (IE research) to show how fast smoke travels through a stack? I know it depends on how raging the fire is but I am simply looking for a base reference. Also, what is the relation to temperature drop over the distance? Once again, I understand there are several factors with the chimney (inside vs outside, insulated, etc etc). I am looking for data concerning outside 2100 chimneys. I am wondering how fast the gases cool off before exiting my system all together. My chimney is 18 feet outside of my house.

Thanks

Andrew

 

[fossil]

I sugggest that if you're really curious, you instrument your system and start taking some data. Never heard of anything like that being available, and there are so many variables involved that I imagine anyone else's results wouldn't mean much for your specific system. Rick

 

[Swedishchef]

I was just wondering if someone has attempted it on their own system. I don't think that a gas' velocity would change that much from one system to the next. I may look into it further, get a few remote thermometers, get equipped and give it a shot later this winter.

A

 

[BrotherBart]

Look part way down the page.

http://www.gulland.ca/florida_bungalow_syndrome.htm

 

[pen]

I wonder if you could take the cap off and hold a hand held anemometer a few inches into the chimney for long enough to measure speed.

http://www.amazon.com/Ambient-Weath...9QCG/ref=sr_1_3?ie=UTF8&qid=1326169579&sr=8-3
http://www.amazon.com/HQRP-Compact-...5K/ref=sr_1_11?ie=UTF8&qid=1326169579&sr=8-11

pen

 

[Huntindog1]

Stove manufacturers seem to mostly go with 6" outlets on their stoves. I reckin because its easier to heat a 6" flue and they are cutting down air flow in these stoves. They are cutting down the air flow not completely shutting it off.

Velocity of the flue gases should be much faster in a 6" rather than a 8" . One thing to consider when venting a 6" outlet stove into an 8" chimney your gonna slow down the velocity. I imagine that keeping the flue gases warm enough so they dont condensate onto the upper part of the chimney is that the hot flue gases get out of the chimney before the smoke has time to cool.

Velocity may be be a factor of difference of potential as in whats the temp difference between the hot stove and the top of the chimney. Maybe that is why when its warm out people complain its hard to get he chimney to draw.

So if your chimney is not drawing good just hang a bag of ice off the top of the chimney. No just kidding

 

[Wood Duck]

The velocity of the air will be a function of the flow rate of the air (volume of air per time). If you could figure out how much air is moving then you'd know the velocity, but I think velocity is easier to measure than flow rate. The flow rate will vary according to the difference in pressure from top to bottom and the resistance to air movement created by the pipe and the stove. Difference in pressure is affected by temperature difference, stack height, and air movement across the top of the stack, among possibly other things.

So, those are the variables in your equation, but that doesn't really help you measure anything. I am sure there is an equation to calculate air flow, but the equation will have some constants that you'll have to estimate, so a calculation you could trust would still require some measurements to verify the constants. If I was going to measure things scientifically I think I'd either measure pressure at top and bottom of the stack and calculate air velocity and flow, or I'd see if there is an air velocity measurement device that could be mounted on the stack without affecting the air movement.

 

[pgmr]

See the Engineering Toolbox Calculator for theoretical answer.

 

[Swedishchef]

PGMR. That is the best answer I have seen in a long time. That link is a very nice website and explains things clearly for even the less scientific type.

I may try to measure the speed Pen, I will let you know how I make out.

Ha ha, piece of ice is on the way to try I will get my wife up there holding it..while I have a beer and take a picture!

A

 

[Huntindog1]

PGMR, yes that was a good website thanks