Secondary Air Distribution System

Re: Secondary Air Distribution System

PostBy: wsherrick On: Tue Nov 26, 2013 5:11 pm

Sunny Boy wrote:wsherrick,

Yes, by "bell-mouthing" the entrance of each feed hole, you will reduce the edge affect and increase airflow - without having to increase the hole size. How you'd do that to all those holes from inside that long tube, I'd be interested to see. ;)

With a bit of experiment, it might even be possible to come up with the correct size feed holes for that size fire bed. The result would be, not having to adjust anything. As draft pressure changes, the air flow volume through the feed holes will change because the air can change speed through the feed holes. If I remember correctly, up to a point. Then, I think resistance increases out of proportion to pressure difference and starts to limit flow. Much like motor speeds can often be limited by the size of the carburetor.

As long as the total flow area of feed holes in the large pipe does not exceed the flow area of the large pipe, the feed holes should pretty well do the self regulating. Size of the feed holes then becomes the question.

See, we're back to "size matters". :D

Paul


I see the logic that you can't have the exit holes add up to a larger area than the main pipe. There has to be some form of natural pressure to create enough force to make the air cover the needed area. Without an induced flow (fan) it would take a keen understanding of how all of these elements work together.
On my Glenwood, which has an over fire secondary air supply, the little holes are not drilled straight through, they are slightly angled and are conical in shape, sort of like tiny funnels. When you can see the flames around the secondary air outlets. They come out horizontal for a few inches then go upward. The flames also move around the combustion chamber in a swirling motion, probably due to the holes being at a slight angle. It would be nice if the research behind this wasn't thrown away when somebody decided to clean out some file cabinets years ago.
My thought was that the goal should be to keep the pressure in the delivery pipe as consistent as possible along the entire thing so to even out the distribution of air. That was my thought behind having smaller holes closer to the front and larger ones near the back.
And I am thinking the same thing as you as far as making it self regulating. If the holes are all the correct size for the fire box then it should be so.
wsherrick
 
Hand Fed Coal Stove: Glenwood Base Heater, Crawford Base Heater
Baseburners & Antiques: Crawford Base Heater, Glenwood, Stanley Argand
Coal Size/Type: Chestnut, Stove Size

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Nov 26, 2013 5:12 pm

Sunny Boy wrote:As draft pressure changes, the air flow volume through the feed holes will change because the air can change speed through the feed holes.

Yes I noticed I can regulate secondary air input also by adjusting my MPD. 8-)
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: wsherrick On: Tue Nov 26, 2013 5:26 pm

I find this discussion interesting. I hope I can learn something here.
wsherrick
 
Hand Fed Coal Stove: Glenwood Base Heater, Crawford Base Heater
Baseburners & Antiques: Crawford Base Heater, Glenwood, Stanley Argand
Coal Size/Type: Chestnut, Stove Size

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Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Nov 26, 2013 5:31 pm

Just for the record, cutting those holes in the front of the furnace was very nerve wracking. I measured the position for those holes at least 5 or 6 times and then still questioned my sanity before continuing with the cut. Those holes are only a quarter inch above the fire brick and a quarter inch inside of the adjacent wall of the fire box AND the pipes had to fit between the water coils and the top of the fire brick. A miscalculation here would have been catastrophic. I'm breathing easier now that its done..
:discuss:
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Nov 26, 2013 5:40 pm

nortcan wrote: My hand drill is ready :D

You be careful with those precious antiques Nortcan!! My furnace was a handicapped second hand unit that nobody wants :lol: ... Now its a lean mean coal burnin machine!!
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: Sunny Boy On: Tue Nov 26, 2013 6:00 pm

wsherrick wrote:
Sunny Boy wrote:wsherrick,

Yes, by "bell-mouthing" the entrance of each feed hole, you will reduce the edge affect and increase airflow - without having to increase the hole size. How you'd do that to all those holes from inside that long tube, I'd be interested to see. ;)

With a bit of experiment, it might even be possible to come up with the correct size feed holes for that size fire bed. The result would be, not having to adjust anything. As draft pressure changes, the air flow volume through the feed holes will change because the air can change speed through the feed holes. If I remember correctly, up to a point. Then, I think resistance increases out of proportion to pressure difference and starts to limit flow. Much like motor speeds can often be limited by the size of the carburetor.

As long as the total flow area of feed holes in the large pipe does not exceed the flow area of the large pipe, the feed holes should pretty well do the self regulating. Size of the feed holes then becomes the question.

See, we're back to "size matters". :D

Paul


I see the logic that you can't have the exit holes add up to a larger area than the main pipe. There has to be some form of natural pressure to create enough force to make the air cover the needed area. Without an induced flow (fan) it would take a keen understanding of how all of these elements work together.
On my Glenwood, which has an over fire secondary air supply, the little holes are not drilled straight through, they are slightly angled and are conical in shape, sort of like tiny funnels. When you can see the flames around the secondary air outlets. They come out horizontal for a few inches then go upward. The flames also move around the combustion chamber in a swirling motion, probably due to the holes being at a slight angle. It would be nice if the research behind this wasn't thrown away when somebody decided to clean out some file cabinets years ago.
My thought was that the goal should be to keep the pressure in the delivery pipe as consistent as possible along the entire thing so to even out the distribution of air. That was my thought behind having smaller holes closer to the front and larger ones near the back.
And I am thinking the same thing as you as far as making it self regulating. If the holes are all the correct size for the fire box then it should be so.


While not as high as forced draft, there's plenty enough pressure drop inside the stove to force enough fresh air into the large pipe. The saving grace is that at such low inches of water pressure inside the stove, it doesn't need high velocity air in the large tubes, so resistance to inside air flow over the length of the large pipes is low. Lower than the flow resistance of the feed holes. This is evident by the fact that you can see evenly sized flames at each feed hole. If the large pipe did have more flow resistance, then the furthest back feed holes would have smaller, or no flames.

Understanding everything about what's happening isn't necessary. Trial and error with feed hole size would still be needed. If it were me, I'd start with say 1/8 inch holes in the 1-1/4 inch pipes, and with no open end restriction on the large pipes. See how the fire reacts over time. Then try enlarging the feed holes and watch again. See if there are any conditions where evidence shows that the feed holes, and/or the large tubes would need some method of manual control .

Plus, by using the aluminum tape to vary the size of the opening in the end of the tubes, you can see how spin dampers, or similar controls at the outboard ends would work. And, sliding a long strip of sheet metal into the tubes to partially block off the feed holes can simulate how the sleeve valves would control air coming in at the feed holes.

Could be an interesting experiment !

Paul
Last edited by Sunny Boy on Tue Nov 26, 2013 6:07 pm, edited 2 times in total.
Sunny Boy
 
Hand Fed Coal Boiler: Anthracite Industrial, domestic hot water heater
Baseburners & Antiques: Glenwood range 208, # 6 base heater, 2 Modern Oak 118.
Coal Size/Type: Nuts !
Other Heating: Oil &electric plenum furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Nov 26, 2013 6:05 pm

wsherrick wrote:I find this discussion interesting. I hope I can learn something here.

Yes, I agree lol I've got more than I bargained for already! I love this forum!! :ugeek:
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Nov 26, 2013 6:07 pm

Sunny Boy wrote:
While not as high as forced draft, there's plenty enough pressure drop inside the stove to force enough fresh air into the large pipe. The saving grace is that at such low inches of water pressure inside the stove, it doesn't need high velocity air in the large tubes, so resistance to inside air flow over the length of the large pipes is low. Lower than the flow resistance of the feed holes. This is evident by the fact that you can see evenly sized flames at each feed hole. If the large pipe did have more flow resistance, then the furthest back feed holes would have smaller, or no flames.

Understanding everything about what's happening isn't necessary. Trial and error with feed hole size would still be needed. If it were me, I'd start with say 1/8 inch holes in the 1-1/4 inch pipes, and with no open end restriction on the large pipes. See how the fire reacts over time. Then try enlarging the feed holes and watch again. See if there are any conditions were you see evidence that the feed holes, and/or the large tubes would need some method of manual control .

Plus, by using the aluminum tape to vary the size of the opening in the end of the tubes, you can see how spin dampers, or similar controls at the outboard ends would work. And, sliding a long strip of sheet metal into the tubes to partially block off the feed holes can simulate how the sleeve valves would control air coming in at the feed holes.

Could be an interesting experiment !

Paul


Amen to all of this! Thank you for sharing your knowledge partner :D
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: titleist1 On: Tue Nov 26, 2013 6:15 pm

Very neat experiment!

as for the intake air control on the pipes if you are still looking for an idea that doesn't use the sleeved pipe...

i am picturing a hose clamp on your pipe very close to the end and a restrictor plate that swings on the screw to cover the end of the pipe. kinda like the one used on a combustion fan intake it would have a hole toward its edge that the screw for the hose clamp would fit through. the screw would be tight enough so the restrictor plate would stay in position as it rotated in place.
titleist1
 
Hot Air Coal Stoker Stove: Harman Mag Stoker (old style) one in basement, one in workshop
Hand Fed Coal Stove: Harman Mark III on standby for long power outages
Coal Size/Type: Rice/Anthracite; Nut/Anthracite

Re: Secondary Air Distribution System

PostBy: wsherrick On: Tue Nov 26, 2013 6:26 pm

Here are two examples of stoves that have heated secondary over fire air. The first example here is a Globe Hot Blast. This stove was designed to burn Bituminous Coal and it has a damper control to regulate how much secondary air gets introduced.

The next example is my Glenwood which has a similar arrangement which differs in that the amount of air is set with the added addition of a separate damper in the door which you can adjust for more secondary air if you want it. The Glenwood is designed to burn Anthracite principally.
I thought you might find this interesting to look at. I find it interesting that this idea is being rediscovered after a hundred years of being forgotten.
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Globe Hot Blast Fire Pot showing heated secondary air inlets.
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Damper for secondary air on Globe Hot Blast.
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Secondary air inlet on the Glenwood. The openings are small and non adjustable.
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Secondary Air Ring on Glenwood. The area behind the little holes for the secondary air is large compared to the size of the exit holes which are funnel shaped.
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wsherrick
 
Hand Fed Coal Stove: Glenwood Base Heater, Crawford Base Heater
Baseburners & Antiques: Crawford Base Heater, Glenwood, Stanley Argand
Coal Size/Type: Chestnut, Stove Size

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Nov 26, 2013 6:26 pm

titleist1 wrote:Very neat experiment!

as for the intake air control on the pipes if you are still looking for an idea that doesn't use the sleeved pipe...

i am picturing a hose clamp on your pipe very close to the end and a restrictor plate that swings on the screw to cover the end of the pipe. kinda like the one used on a combustion fan intake it would have a hole toward its edge that the screw for the hose clamp would fit through. the screw would be tight enough so the restrictor plate would stay in position as it rotated in place.

Oh yes, very good suggestion!! I'll consider this too. Thank you! :D
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: Sunny Boy On: Tue Nov 26, 2013 6:28 pm

Lightning wrote:
Sunny Boy wrote:
While not as high as forced draft, there's plenty enough pressure drop inside the stove to force enough fresh air into the large pipe. The saving grace is that at such low inches of water pressure inside the stove, it doesn't need high velocity air in the large tubes, so resistance to inside air flow over the length of the large pipes is low. Lower than the flow resistance of the feed holes. This is evident by the fact that you can see evenly sized flames at each feed hole. If the large pipe did have more flow resistance, then the furthest back feed holes would have smaller, or no flames.

Understanding everything about what's happening isn't necessary. Trial and error with feed hole size would still be needed. If it were me, I'd start with say 1/8 inch holes in the 1-1/4 inch pipes, and with no open end restriction on the large pipes. See how the fire reacts over time. Then try enlarging the feed holes and watch again. See if there are any conditions were you see evidence that the feed holes, and/or the large tubes would need some method of manual control .

Plus, by using the aluminum tape to vary the size of the opening in the end of the tubes, you can see how spin dampers, or similar controls at the outboard ends would work. And, sliding a long strip of sheet metal into the tubes to partially block off the feed holes can simulate how the sleeve valves would control air coming in at the feed holes.

Could be an interesting experiment !

Paul


Amen to all of this! Thank you for sharing your knowledge partner :D


Your very welcome. I'm also interested to see what results you get.

Paul
Sunny Boy
 
Hand Fed Coal Boiler: Anthracite Industrial, domestic hot water heater
Baseburners & Antiques: Glenwood range 208, # 6 base heater, 2 Modern Oak 118.
Coal Size/Type: Nuts !
Other Heating: Oil &electric plenum furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Nov 26, 2013 6:33 pm

wsherrick wrote:Here are two examples of stoves that have heated secondary over fire air. The first example here is a Globe Hot Blast. This stove was designed to burn Bituminous Coal and it has a damper control to regulate how much secondary air gets introduced.

The next example is my Glenwood which has a similar arrangement which differs in that the amount of air is set with the added addition of a separate damper in the door which you can adjust for more secondary air if you want it. The Glenwood is designed to burn Anthracite principally.
I thought you might find this interesting to look at. I find it interesting that this idea is being rediscovered after a hundred years of being forgotten.

Thank you!! I knew my idea of distributing secondary air wasn't something new, but seems like you won't find a current stove that employs it. Thank you for the pics! Its neat to see how they did it long ago. I would assume too that my secondary air is "preheated" since when I look down the pipe from the front of the furnace, I can see the distortion of the heated air in the pipe in front of the plug on the other side of the pipe. :D
Last edited by Lightning on Tue Nov 26, 2013 7:41 pm, edited 1 time in total.
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: wsherrick On: Tue Nov 26, 2013 6:45 pm

You're welcome. I'm fairly sure that the pipe is plenty hot enough to heat the incoming air as soon as it gets in there. The prevailing idea is that the air needs to be hot so it will not rob heat from the fire before it is able to get hot enough to burn the gas effectively and the draft takes it and the unburned gasses up the chimney. Hence the importance of having the air as near the top of the fire bed as possible.
Germer Stove Company had another concept of introducing the hot secondary air right into the fire bed instead of over it. Their fire pot had vertical slits from bottom to top cut into the sides of the fire pot. The air was introduced that way. I don't know which system worked better.

Here is a rusty example of the Germer Hotblast design for secondary air.
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Top look downward of Germer Fire pot. Notice tubes cut into slits to allow secondary air right into the fire bed itself.
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Last edited by wsherrick on Tue Nov 26, 2013 6:53 pm, edited 1 time in total.
wsherrick
 
Hand Fed Coal Stove: Glenwood Base Heater, Crawford Base Heater
Baseburners & Antiques: Crawford Base Heater, Glenwood, Stanley Argand
Coal Size/Type: Chestnut, Stove Size

Re: Secondary Air Distribution System

PostBy: michaelanthony On: Tue Nov 26, 2013 6:52 pm

Delivery man by day and doctor of physics by night :up: I enjoy your "hootspa", I sure I spelled it wrong. Before you take off to your isle of solitude, could you attach a metal electrical box to the end of the conduit and cover with a solid steel cover and make your own "check damper"? Simular to Mr. Precision's avatar. Keep on truckin' Clark Kent! 8-)
michaelanthony
 
Hand Fed Coal Stove: Vigilant 2310, gold marc box, vogelzang pot belly coat rack
Coal Size/Type: Pea, and a little nut
Other Heating: Very cold FHA oil furnace

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