Increasing air speed and/or flow

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Hoytman
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Post by Hoytman » Fri. Jul. 24, 2020 10:46 am

This will be a good one for Isayre, McGiever, others interested...

Does anyone have any idea if air speed, and/or flow (I say that because they can likely be different, but I don't know), can be increased without mechanically inducing it? Likely not, but I thought I'd ask.

Sounds like a silly question, but I'm thinking of this in regard to stoves and chimney's, mainly a stove or outdoor fire pit. Obviously, if this could be done, then there would be no need of electrical/mechanical draft inducers, but I'm hoping I am wrong.

I'm wondering if creating a vortex, like in some of the rocket stoves, induces better air speed as heat increases? This is what I'm driving at. However, I'm also thinking along the lines of the cold intake side as well as exhaust.

It could be that a small or large fan is the only way to do this.

When I was a kid I remember this little toy I had. It was a short 1"-2" piece of plastic tubing about 1/2" inside diameter. You could barely blow on it to turn this little super-duper-dyno-whoppin' little thing-a-ma-bob inside of it that made this little whizzing noise....zzzzzzzzzz. Sort of reminded me a jet engine...and I don't know anything about jet engines or turbines, but they are interesting and fascinating.

Seems like back when I worked maintenance in a machine shop, that some of the machinists told me that air moving through a hole can be increased slightly by putting a bevel on both the hole entrance and exit point....countersinking it is the word I'm looking for. Also, I remember that there's a space around the outer edge of the hole where air has some "resistance"...maybe that's the word I'm looking for to describe it???

There has to be some sort of applied physics here, but that is one course I never took and know little about. Very little. I just know of very basic things and I'd likely even get those wrong. :lol: :mrgreen:



https://www.google.com/search?ei=aPEaX5XQJI24tAat ... CAw&uact=5


I am wondering if somehow these thoughts can be applied as well.
https://physics.stackexchange.com/questions/13030 ... an-airfoil

 
Hoytman
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Post by Hoytman » Fri. Jul. 24, 2020 11:02 am

Post above edited several times. I think I got it where I want it. LOL!!!

 
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Post by johnjoseph » Fri. Jul. 24, 2020 11:06 am

Improved draft should increase draw. I have improved draft with a 4ft extension on my chimney and adjusting my barometric draft accordingly. I also decreased from 3 elbows down to 2 which helped as well. I Should have done all that to begin with. My initial year of burning was at 6 tons usage changes made second year and now at 4 tons usage. I'm not an expert like others on here, but what I've done seems to have worked.

 
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Post by freetown fred » Fri. Jul. 24, 2020 11:25 am

Damn H, here I thought ya might give that brain of yours a break this summer???????????? :)
Hoytman wrote:
Fri. Jul. 24, 2020 10:46 am
This will be a good one for Isayre, McGiever, others interested...

Does anyone have any idea if air speed, and/or flow (I say that because they can likely be different, but I don't know), can be increased without mechanically inducing it? Likely not, but I thought I'd ask.

Sounds like a silly question, but I'm thinking of this in regard to stoves and chimney's, mainly a stove or outdoor fire pit. Obviously, if this could be done, then there would be no need of electrical/mechanical draft inducers, but I'm hoping I am wrong.

I'm wondering if creating a vortex, like in some of the rocket stoves, induces better air speed as heat increases? This is what I'm driving at. However, I'm also thinking along the lines of the cold intake side as well as exhaust.

It could be that a small or large fan is the only way to do this.

When I was a kid I remember this little toy I had. It was a short 1"-2" piece of plastic tubing about 1/2" inside diameter. You could barely blow on it to turn this little super-duper-dyno-whoppin' little thing-a-ma-bob inside of it that made this little whizzing noise....zzzzzzzzzz. Sort of reminded me a jet engine...and I don't know anything about jet engines or turbines, but they are interesting and fascinating.

Seems like back when I worked maintenance in a machine shop, that some of the machinists told me that air moving through a hole can be increased slightly by putting a bevel on both the hole entrance and exit point....countersinking it is the word I'm looking for. Also, I remember that there's a space around the outer edge of the hole where air has some "resistance"...maybe that's the word I'm looking for to describe it???

There has to be some sort of applied physics here, but that is one course I never took and know little about. Very little. I just know of very basic things and I'd likely even get those wrong. :lol: :mrgreen:



https://www.google.com/search?ei=aPEaX5XQJI24tAat ... CAw&uact=5


I am wondering if somehow these thoughts can be applied as well.
https://physics.stackexchange.com/questions/13030 ... an-airfoil


 
Hoytman
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Post by Hoytman » Fri. Jul. 24, 2020 11:34 am

johnjoseph wrote:
Fri. Jul. 24, 2020 11:06 am
Improved draft should increase draw.
I agree, but I am thinking in terms of secondary air and firebox turbidity or turbulence. Initially, these thoughts were "sparked" by considering how to increase a secondary burn on an open fire pit...say via a metal fire ring inside of another ring and welded at the top. The outside ring would have adjustable air intake low on the outside ring, and the inner ring would have outlet holes drilled into the inside of the inner fire ring. Obviously, some of the newer outdoor fire rings are made in a similar fashion. I could buy one, but I'm thinking about building my own and thinking a vortex inside the two rings might just increase velocity as heat increases. Then I started wondering if a similar principal could be induced inside the fire chamber of a stove. Again, some stoves have relatively slow and straight flames coming from secondary air chambers, yet while others I have seen, especially some of those British stoves, like the Burley and others, have extreme turbulence inside the firebox. I am thinking the more extreme the turbulence, the more time the flames have to burn the smoke making for a cleaner burn...which is what I am thinking of with the outdoor fire pit. I'm tired of getting smoked out and/or having to move my chair. :lol: Plus, you might get a more interesting outdoor fire display...not to mention the benefits of a similar line of thought contained within a stove. Not trying to re-invent the wheel here...but you never know. :lol:

https://www.bbqguys.com/solo-stove/bonfire-19-5-i ... teel-ssbon

I think the fire in this below could be made better...


Then again, it may chew through wood way too fast as well. What I have in mind may be applicable to firebox inside a stove, and may be best suited to a cylindrical stove...no doubt.

Ok...I've written enough. I want to see what others have to say.

 
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Post by Sunny Boy » Fri. Jul. 24, 2020 12:13 pm

Hoytman wrote:
Fri. Jul. 24, 2020 10:46 am
This will be a good one for Isayre, McGiever, others interested...

Does anyone have any idea if air speed, and/or flow (I say that because they can likely be different, but I don't know), can be increased without mechanically inducing it? Likely not, but I thought I'd ask.

Sounds like a silly question, but I'm thinking of this in regard to stoves and chimney's, mainly a stove or outdoor fire pit. Obviously, if this could be done, then there would be no need of electrical/mechanical draft inducers, but I'm hoping I am wrong.

I'm wondering if creating a vortex, like in some of the rocket stoves, induces better air speed as heat increases? This is what I'm driving at. However, I'm also thinking along the lines of the cold intake side as well as exhaust.

It could be that a small or large fan is the only way to do this.

When I was a kid I remember this little toy I had. It was a short 1"-2" piece of plastic tubing about 1/2" inside diameter. You could barely blow on it to turn this little super-duper-dyno-whoppin' little thing-a-ma-bob inside of it that made this little whizzing noise....zzzzzzzzzz. Sort of reminded me a jet engine...and I don't know anything about jet engines or turbines, but they are interesting and fascinating.

Seems like back when I worked maintenance in a machine shop, that some of the machinists told me that air moving through a hole can be increased slightly by putting a bevel on both the hole entrance and exit point....countersinking it is the word I'm looking for. Also, I remember that there's a space around the outer edge of the hole where air has some "resistance"...maybe that's the word I'm looking for to describe it???

There has to be some sort of applied physics here, but that is one course I never took and know little about. Very little. I just know of very basic things and I'd likely even get those wrong. :lol: :mrgreen:



https://www.google.com/search?ei=aPEaX5XQJI24tAat ... CAw&uact=5


I am wondering if somehow these thoughts can be applied as well.
https://physics.stackexchange.com/questions/13030 ... an-airfoil
Interesting questions that have been kicked around on here in some threads.

Your comparing "naturally aspirated" to forced induction (fan-fed). Naturally aspirated just means no mechanical help, only natural differences in pressure does all the work. With a stationary object like a stove the driving force is the pressure difference we call "draft", or some call it "vacuum" or "suction", but technically it is known as "pressure drop". However, you rarely hear that term used outside of auto fuel/air intake system designers. But all are the same thing. You can find out more by looking up those other terms.

And how well it does that pressure drop is mostly do to temperature difference of the gas (air) outside the stove/chimney system verses the lighter hot exhaust inside the stove/chimney system. The hotter the exhaust, the faster it will flow because of greater pressure difference. Trying to increase that can be done by reducing flow resistance into, through the fuel bed, and then out of the system. But that does not give as much gains as temperature difference if the system is already decent. Where you'd see the biggest change is on differences of coal size, as anyone who has tried different sized coal in their stove likely has learned.

But all that is limited. To get greater gains takes mechanically increasing the pressure difference. BTW to get more out of the coal fired boilers of steam ships they went to using ducted fan systems for pressurizing the air in boiler rooms. So, even with the best, expensive, naturally aspirated designs, they have their limits. And that's why they have super charges and turbos on engines. However, I doubt there is enough energy in stove exhaust to drive a stove turbo if anyone is thinking of hot-rodding their 3.5 liter Glenwood. :lol:

That bevel, or rounding of an edge of a hole, that a gas is to flow through, reduces what is known as ''edge effect". It's one of the elements that goes into carburetor and intake system designs. You see it in the trumpet shaped openings at the top of carburetor throttle bores. Edge effect is caused by turbulence created drag at the very edge of a hole (only within a few thousands of an inch) as air tries to flow in and gets mixed with air not wanting to move right at the edge. Because the effect is always close to the edge and about the same size, it's not much of a factor on large openings as small ones. I learned about this when designing a redistribution plate for a carburetor/turbocharger box when designing a turbo system for my 72 AMX. Needed the plate with 1/4 inch holes to redirect and even out air/fuel flow only coming into one the side of the box and having to make a tight 90 degree turn to go down into the top of the intake manifold. Without the redistribution plate most of the fuel vapor in the air/fuel mix would be thrown to one side of the intake manifold plenum area and thus feeding four cylinders too rich, leaving the other four cylinders too lean. Even though that air/fuel mix was being boosted to higher pressure/force by the turbo, calculations showed that I had to add at least 25% more holes to compensate for the total square area of openings in the plate lost to edge effect drag just to flow the same CFM as without the plate.

The Rocket stoves "rocket" because they are burning a hot fast burning fuel - wood kindling. Fill them with coal and see if they still rocket. You'd see the same if you had a stove like those of us that have antique stoves that burn both wood and coal. As you know, wood burns too fast to get as long and steady of a fire as coal can in the same stove.

As for why an airfoil works, look up Bernoulli affect and then think about if any of that applies to stoves. ;)

Paul

 
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Post by carlherrnstein » Fri. Jul. 24, 2020 5:12 pm

A vortex slows down flow. I have seen tanks fitted with "vortex beakers" at drain bungs. One thing a vortex will do is mix fuel and air which is desirable for complete combustion. A vortex can also seperate heavier things out like a centrifuge as in a cyclonic separator.

As for a countersink on a orifice I have made parts for a vacuum system that were countersunk to a sharp edge on the small side. The small side was the higher pressure side.

Supposedly when a gas flows though a hole the gas at the edge of the hole rolls like a smoke ring and can restrict flow to a degree. If the hole is countersunk and the higher pressure is on the small side the "smoke rings" expand as they follow the angle of the hole and dissipate allowing the next "ring" to form and flow out of the way. Otherwise the "rings" sort of pile up and slow the flow.

Don't quote that as gospel that is just the quick explanation I got on how it works several years ago.

 
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Post by lsayre » Fri. Jul. 24, 2020 6:44 pm

The trick is to make your homes chimney a better chimney than is your home itself. One must thereby find solutions that allow for a stove to receive more "stack effect" and less "my house acts like it's a better chimney than my chimney" effect. The only time my homes CO detectors ever went off was when "one day" we turned the whole house fan on during the summer (we ran our coal boiler year round for DHW) and thereby made the pressure within the house lower than the outside pressure whereby the chimney started working in reverse in an effort to re-pressurize the low pressure house. One time was enough and the whole house fan was never used again. Even a bathroom fan or a dryer vent can do this highly undesirable deed.

What is needed is for more air coming in and less air going out at the plane of the stove. Cracking open a window at the level of the stove is one way to make the stoves chimney work as a better chimney than the house. Another way is to install a goodly diameter duct that feeds the stove with outside air, and place its terminus near but not directly at the stoves air inlet. A damper placed within this duct assures that the flow is going only in the direction that is beneficial. The stove needs to breath in more incoming air than any other chimney than it's own chimney (these other chimneys being the homes attic ridge vent, a whole house fan, a bathroom fan, a dryer vent, etc...) can simultaneously exhaust.

There is an entire science of natural "pressure planes" existing within a house, whereby the most neutral pressure plane is generally found to be somewhere near its mid height level, and stoves at this mid level often breath better than if in the basement. This pressure plane science tends to state that the lowest pressure level in a home is the toughest area whereby to accomplish higher pressure than exists outside, and since the homes basement is generally by nature the homes lowest pressure point, and the stoves chimney needs to be the homes lowest pressure point, the two often don't mix, and in this case it is sometimes better to move the stove upstairs to a more neutral pressure plane. This science can be very confusing. At least it is for me. Lee (Lightning) has a better grasp of it than I do.


 
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Post by McGiever » Fri. Jul. 24, 2020 7:02 pm


 
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Post by Sunny Boy » Fri. Jul. 24, 2020 7:13 pm

Now, Bill,... aren't you glad you asked? The not-so-simple-science of stoves. :lol:

Paul

 
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Post by Hoytman » Fri. Jul. 24, 2020 11:42 pm

McGiever wrote:
Fri. Jul. 24, 2020 7:02 pm
Bill,

Some reading for your entertainment:

Basics: https://erc.cals.wisc.edu/woodlandinfo/files/2017 ... 8405hr.pdf

Peruse:
https://www.google.com/search?q=superheated+secon ... 8&hl=en-us
That second link...been looking and researching many of those ideas for a few years now, but thank you for the link as I have found many new interesting things while looking. Didn’t realize they showed that many diagrams of stove innards and air flow paths of so many stoves. Thanks again!

 
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Post by Hoytman » Fri. Jul. 24, 2020 11:43 pm

Sunny Boy wrote:
Fri. Jul. 24, 2020 7:13 pm
Now, Bill,... aren't you glad you asked? The not-so-simple-science of stoves. :lol:

Paul
:lol:

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