Rhonemas said:
Maybe implied here? Radian't heat of the fire itself does go through the glass...just like the light does.
Emissivity (basic facts about heat radiation)
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Maybe implied here? Radian't heat of the fire itself does go through the glass...just like the light does.
Dylan said:
radient heat is just that , radiated from a fixed object, convective heat is heat transferred to the surrounding air, conducted heat is the heat that passes through a substance, you cannot have "radient heat " without "conducted heat" different surfaces conduct heat at different levels of resistance like insulation traps heat your "r factor" steel will refract or allow less heat to pass through it , than glass, so more heat is conducted , and radiated, through glass. convective heat, or heat transfer into air is based on the amount of thermal energy that is imparted to it by a hot surface it is in or close to in contact with. heat transfer to air works this way. air will accept heat easily up to a certain point but diffuses(or disperses) heat easily as well. this is where convective heat has an advantage heating a large area. heat that is radiated causes natural air currents in an inclosure , this current is a "blooming" current, which causes an updraft above the heat source that when contacting the ceiling, spreads radially from where it comes in contact. this pushes air outward and eventually down as the air cools. now the air that cools is drawn across the floor towards the updraft created by the heat source and the bloom current, this is a convection current. a blower assisted unit will spread heat more easily in a room due to moving the radiated heat over a wider area faster which will speed up the convection current artificially. which allows a larger area to be heated more repidly. a way to see how convection currents work , take a lit match and hold it in a doorway leading out of the room that contains the heat source. if you hold the match( or lighter) high in the doorway , the flame should lean into the other room, as you move the flame downwards it stands up , and then as it nears the floor, it leans toward rthe room with thge heat source in it.
essentially there are arguements for which is better , but what it all boils down to is the application, and how eficiently the convection currents work in each application. one house will not work as well as the one next door or vice /versa. floor plan , heat source location and insulation factors are still the deciding factor in how well a point source heater will work.
ok, convective heat transfer, air as well as fluids have differing densities as well due to temperature, convection would be that transfer you are right , but it is not limited to liquids alone, if so explain to me how a "convection oven" works, there are no liquids present.
You guys are giving me a headache! There are only so many BTU's in each split of wood. You can't increase the BTU's from convection or radiation. You will get the same amount of BTU's per pound of wood. The different kinds of stoves will give off the same BTU's. Some faster or slower than others. Too many variables.
Well, really, to make use of this info, forget about the wood! It's about defining the outer boundaries (i.e. the best possible case) of heat output for a given stove size, and how you'll have to operate it to get that.Todd said:
Roospike said:
You have to be careful here... the thermal conductivity through the steel is not going to be your rate limiting step in a wood stove application.
You have multiple stages of heat transfer happening in series. First, you have to transfer heat from the combustion source to the steel plate. Second, you have conduction of heat through the steel plate. Third, you have convective and radiative transfer off the steel plate to the surrounding environment.
Whether 1/16" or 1" thick steel, that second conduction step is going to be so efficient that it will not have any significant impact on how the stove heats the room in steady-state operation. The rate limiting steps will be the transfer of heat into and out of the steel plate - not through it.
You will of course have a subtle difference at the beginning of the fire and the end, as the extra steel will hold an incremental amount of additional BTUs. But this will be a relatively small factor compared to the total BTUs that you generate with one large load of wood.
Finally, it is worth noting that some stove designs do actually include internal air gaps within the firebox construction to further modify the heat transfer rate. But fireboxes with simple slabs of steel, iron, or stone won't be all that different in how they behave, whether 1/16" or 1" thick.
-Colin
OK so far.NY Soapstone said:
Well, it's not that simple. Your first stage should include firebox liners (firebrick or cast), internal chambers and air passageways, and the like, all the things that EPA stoves use to burn clean. I've never seen a single EPA stove that has even 50% of it's flame path directly exposed to an unprotected outer surface.
I don't think so, for two reasons. First, there is no such thing as "steady state operation" in a woodstove. It's a burn "cycle." Second, you're ignoring the effect of thermal mass on conductivity. I know from experience that it has a big effect on "how the stove heats the room" as you put it.
Example: Two identical size and shaped cast iron stoves. One weighs 115 lbs, the other 165. The external castings are the same thinkness. The difference? The second one has far more substantial firebox liners (also cast iron) weighing 50 lbs more. With the same load of wood, you could burn an intense fire in either one for an hour or so. The lighter unit put out MUCH more heat during that time than the heavier one, more than 200-300 degrees more as measured on the top plate. 30-45 minutes after the flames have dies, the heavier unit would be giving off more heat. But I don't consider a stove sitting at 300F to be giving useable heat. I agree with Elk, unless it's a huge stove, once you get below 450 it's not giving you much.
That's not what I experience. And...we no longer burn such simple stoves as you describe.
Okay, riddle me this Batman.............
When the 2 splits from My Summit "radiate, convect & blow" against the radiant heat from the nuke plant forming a wall of super conducted molecular meltdown, what kind of heat is that? How many BTU's, and how long will it burn for????????
Further more.......... If I eat green eggs & ham, can I also get green bacon & spam to go along with it?
And lastly, why, on a heart forum, am I noticing a constant strive of folks trying to sound like f'in nuclear chemists & rocket scientists?
A legit post turns into a godayum debate over big words & figures.
Wait
! I think the Summit has the edge over the nuke plant, "Shes pushing them back captain, but she cont handl much morellll!!
I'll have to out some dilythium crystals in the Summit now and hope she cools by June!
BURP!
When the 2 splits from My Summit "radiate, convect & blow" against the radiant heat from the nuke plant forming a wall of super conducted molecular meltdown, what kind of heat is that? How many BTU's, and how long will it burn for????????
Further more.......... If I eat green eggs & ham, can I also get green bacon & spam to go along with it?
And lastly, why, on a heart forum, am I noticing a constant strive of folks trying to sound like f'in nuclear chemists & rocket scientists?
A legit post turns into a godayum debate over big words & figures.
Wait
! I think the Summit has the edge over the nuke plant, "Shes pushing them back captain, but she cont handl much morellll!!I'll have to out some dilythium crystals in the Summit now and hope she cools by June
!BURP!
Hog, Forget about your darn summit for a minute, we all know you love said stove 
I want to hear more about the 16' wall Dylan made out of coils of chicken wire!
I want to hear more about the 16' wall Dylan made out of coils of chicken wire!
* That quote is crazy talk unless one is talking about how the "fire" behaves then true but you can not put the same heat to two different thicknesses and have it show the same properties of heat out put or how it behaves then same.precaud said:
Here ya go geniuses,
HAVE AT IT!!
Can someone dump this crap to the ash can now please?
Heat energy transferred between a surface and a moving fluid at different temperatures is known as convection.
In reality this is a combination of diffusion and bulk motion of molecules. Near the surface the fluid velocity is low, and diffusion dominates. Away from the surface, bulk motion increase the influence and dominates.
Convective heat transfer may take the form of either
* forced or assisted convection
* natural or free convection
Forced or Assisted Convection
Forced convection occurs when a fluid flow is induced by an external force, such as a pump, fan or a mixer.
Natural or Free Convection
Natural convection is caused by buoyancy forces due to density differences caused by temperature variations in the fluid. At heating the density change in the boundary layer will cause the fluid to rise and be replaced by cooler fluid that also will heat and rise. This continues phenomena is called free or natural convection.
Boiling or condensing processes are also referred as a convective heat transfer processes.
* The heat transfer per unit surface through convection was first described by Newton and the relation is known as the Newton's Law of Cooling.
The equation for convection can be expressed as:
q = h A dT (1)
where
q = heat transferred per unit time (W)
A = heat transfer area of the surface (mo)
k = convective heat transfer coefficient of the process (W/m2K or W/m2oC)
dT = temperature difference between the surface and the bulk fluid (K or oC)
Convective Heat Transfer Coefficients
The convection heat transfer coefficient - k - is dependent on the type of media, gas or liquid, the flow properties such as velocity, viscosity and other flow and temperature dependent properties.
In general the convective heat transfer coefficient for some common fluids is within the ranges:
* Air : 10 - 100 (W/m2K)
* Water : 500 - 10,000 (W/m2K)
Example - Convective Heat Transfer
A fluid flows over a plane surface 1 m by 1 m with a bulk temperature of 50oC. The temperature of the surface is 20oC. The convective heat transfer coefficient is 2,000 W/m2oC.
q = (2,000 W/m2oC) ((1 m) (1 m)) ((50oC) - (20oC))
= 60,000 (W)
= 60 (kW)
HAVE AT IT
!!Can someone dump this crap to the ash can now please?
Heat energy transferred between a surface and a moving fluid at different temperatures is known as convection.
In reality this is a combination of diffusion and bulk motion of molecules. Near the surface the fluid velocity is low, and diffusion dominates. Away from the surface, bulk motion increase the influence and dominates.
Convective heat transfer may take the form of either
* forced or assisted convection
* natural or free convection
Forced or Assisted Convection
Forced convection occurs when a fluid flow is induced by an external force, such as a pump, fan or a mixer.
Natural or Free Convection
Natural convection is caused by buoyancy forces due to density differences caused by temperature variations in the fluid. At heating the density change in the boundary layer will cause the fluid to rise and be replaced by cooler fluid that also will heat and rise. This continues phenomena is called free or natural convection.
Boiling or condensing processes are also referred as a convective heat transfer processes.
* The heat transfer per unit surface through convection was first described by Newton and the relation is known as the Newton's Law of Cooling.
The equation for convection can be expressed as:
q = h A dT (1)
where
q = heat transferred per unit time (W)
A = heat transfer area of the surface (mo)
k = convective heat transfer coefficient of the process (W/m2K or W/m2oC)
dT = temperature difference between the surface and the bulk fluid (K or oC)
Convective Heat Transfer Coefficients
The convection heat transfer coefficient - k - is dependent on the type of media, gas or liquid, the flow properties such as velocity, viscosity and other flow and temperature dependent properties.
In general the convective heat transfer coefficient for some common fluids is within the ranges:
* Air : 10 - 100 (W/m2K)
* Water : 500 - 10,000 (W/m2K)
Example - Convective Heat Transfer
A fluid flows over a plane surface 1 m by 1 m with a bulk temperature of 50oC. The temperature of the surface is 20oC. The convective heat transfer coefficient is 2,000 W/m2oC.
q = (2,000 W/m2oC) ((1 m) (1 m)) ((50oC) - (20oC))
= 60,000 (W)
= 60 (kW)
And lastly, convection form a source of heat,
formulas & all, knock yourselves out Einsteins:
A heat source, like a big engine, stove or melting pot, will generate a convective vertical air flow.
convective heat flow source
Air Velocity
The air velocity in the center of the air flow in a distance above the floor can be calculated as
vc = c1 ( 1000 P / l )1/3 (1)
where
vc = air velocity in the center of the air flow (m/s)
c1 = constant characterizing the actual application, typical values between 1 to 2.
P = heating power from the source (W)
l = distance above the floor and the heat source (m)
Air Flow Volume
The air flow in a distance above the the floor can be calculated as
Q = c2 P1/3 l5/3 (2)
where
Q = air flow volume (m3/s)
c2 = constant characterizing the actual application, typical values between 0.05 to 0.15
formulas & all, knock yourselves out Einsteins:
A heat source, like a big engine, stove or melting pot, will generate a convective vertical air flow.
convective heat flow source
Air Velocity
The air velocity in the center of the air flow in a distance above the floor can be calculated as
vc = c1 ( 1000 P / l )1/3 (1)
where
vc = air velocity in the center of the air flow (m/s)
c1 = constant characterizing the actual application, typical values between 1 to 2.
P = heating power from the source (W)
l = distance above the floor and the heat source (m)
Air Flow Volume
The air flow in a distance above the the floor can be calculated as
Q = c2 P1/3 l5/3 (2)
where
Q = air flow volume (m3/s)
c2 = constant characterizing the actual application, typical values between 0.05 to 0.15
If you don't like the conversation, why don't you just move on to the next thread, dude?Hogwildz said:
precaud said:
Um, cause this is a public forum, and being a member, I have the right to view the threads and respond, dude.
I honestly had to search and find the convective heat info , which btw was very easily found. I don't claim to know much about it other than what I found during my research. Whats your qualifications for posting you facts? Did you do the same as me, research and grab from other info found online? Comon be honest?
precaud said:
Actually, that extra level of internal complexity you describe strengthens the same point I was making - any additional obstacles to direct heat transfer from fire to wall adds more high resistance components when it comes to a heat transfer "circuit." Introductory level heat transfer courses often use analogies to electrical circuits to help illustrate this concept. The conduction of heat through the steel plate is much much faster than the other processes involved. So the thickness does not really matter when you're on the order of an inch, which is what I was getting at.
I would agree with you that in a poorly designed stove that can't regulate draft/air controls, you are right. But a well designed stove that regulates combustion air does approach this ideal with long burn times where the burn rate is quite stable. That is what most people end up aiming for - that's why you see everyone talking about how long they can burn.
By the way, I do agree that all of these analysis are technical simplifications, and if we really wanted to be correct, we'd do finite element 2D models, etc. etc. etc. to prove a theory, but I am trying to simplify the explanation because not everyone on here is an engineer. In the end, it's a fairly basic concept that can give sound intuition to more complex scenarios.
Your statement of how slow the heat transfer is off a 300 F stove surface really gets back to the core point I'm trying to outline. Heat won't move off that 300 F stove very quickly at all - I agree. This is because the convective/radiative transfer is very slow. That's why you can easily hold your hand 2" away from a 300F stove without any problem.
Now take a guy like Roo (who I think does a lot of metal work) and ask him how long he'd hold his bare hand to a 1/2" thick piece of steel with a 300 F torch on the back side. He would probably tell you it would hurt like hell within a minute or less - and in either case, it would hurt a lot sooner than holding his hand near (but not on) that 300 F stove. This is because you're now back to conductive heat transfer - just like through that stove wall. My point is that the conductive equilibrium through the steel wall happens rapidly - so much more so than anything else involved in the heat transfer, that the thickness doesn't play a significant role in the overall heat transfer behavior of the stove.
I'll have to look around on the internet to see if I can find a good picture illustrating the concept.
-Colin
disclaimer: Roo - please do not misinterpret my comments and become defensive that I am slamming a particular stove. This fundamental principle is not all that different with with 1/2" thick steel or 1/2" thick soapstone. I am only pointing out that in a heat transfer "series" type circut as exists in a modern stove, the rate of conduction through that wall makes no appreciable difference in the rate of heat transfer through the stove - the other steps in the heat transfer are really what limit you, and those other steps are where manufacturers start to differentiate from each other. The types of air gaps (or lack thereof), air passages, firebricks, intended surface operating temperature, etc... all play a much bigger role in regulating how fast heat gets out into the room in the end analysis.
Roospike said:
Roo, if you took your exact same stove you have today and cut the steel wall thickness in half, you would see no significant difference in how the heat transfer behaved. I know it's not an immediately intuitive concept; I tried to explain it again in another post.
Of course I wouldn't recommend having a thin walled stove for other reasons - you would clearly have a much weaker stove that would be incredibly dangerous, so for that reason alone, it's a damn good thing they're built thick, and you can still be glad that yours has a thicker wall than many others on the market
One other thing that might be interesting to you since you mention the mass of stoves as being important to consider.
First, how much heavier do you suppose your PE stove is compared to whatever a low grade knockoff might weigh? Let's be generous - 250 lbs more?
Next, how many more BTUs do you think you are packing away and storing in that extra 250 lbs of stove, assuming all that difference is steel, when you have the stove at 450 degrees?
Does the answer seem like a lot of BTUs to you when compared to the number of BTUs per hour your stove is putting out when it's got a fire in it?
If you can find the numbers, repeat the analysis with soapstone.
The result might surprise you, and give you some interesting ammunition when you go after soapstone owners too
-Colin
NY Soapstone said:
One of the things I have been curious about. While damn sure not willing to call my Englander a "low grade knockoff" it is approximately the same size as Spike's Summit Classic but while the Summit has a 3/8" top and 1/4" sides and the NC-30 has 1/4" top and 3/16 sides, the Summit is only 20 pounds heavier? Does not make sense.
BrotherBart said:
Size BB, size. Your firebox alone is 3.5 compared to our 3.0 cf. I think your stoves dimensions are larger also. So although the Summits have thicker steel, you have more steel.
BrotherBart said:
PE Summit 3.0 cf firebox weight 475lbs. Dimensions: 25 1/2" W x 29 1/4" H x 23 1/2" D
vs
Englander 3.5 cf firebox weight 455lbs. Dimensions: 23 1/4" W x 27" H x 24 1/2" D
BrotherBart said:
Hmmm, well its got to be there somewhere. You have refractory brick on top as baffle? How does that compare to the s.s. on the Summit? I'd say legs, ashpan etc, but thats only against the insert, no arguement there with the Summit FS.. Wih a 1/2 a cf larger firebox its only a theres no major difference there? How bout height? More metal there? Its there, just have to find the difference. The Summit door is cast, is the Englander also cast?
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