Does black painted stainless steel radiate heat better than the same plain clean stainless steel metal?
Does black stainless radiate heat better than clean metal?
- Thread starter DriftWood
- Start date
-
Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.
We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.
We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil. -
Super Cedar firestarters 30% discount Use code Hearth2024 Click here
- Status
Yes, and no. Radiation will be higher, but convection will be the same. Convection acounts for the bulk of the heat transfer, though - it's a faster process
well, since i assume the interior of the stove to be unpainted, I also assume its the exterior you speak of. Since the heat is from within, and it has to proceed thru the steel b4 it ever reaches the black, blue, or white paint, i wouldnt think it would matter. Since energy is conserved, after it hits the steel it has to go somewhere......and youre saying if the paint is black, it gets reflected, whereas if its light, it doesnt? Seems kinda odd there. I agree any paint might have some minimal insulating characterisitics, but stove color or pipe color for that matter really shouldnt matter here.
Energy from light, for instance, is more readily absorbed by darker colors, and thereby converted to heat, but in this case, where we have heat as the form of energy in the first place, I wouldnt think it would matter.....
Energy from light, for instance, is more readily absorbed by darker colors, and thereby converted to heat, but in this case, where we have heat as the form of energy in the first place, I wouldnt think it would matter.....
I dont think it makes any difference, and if it did, except in a lab, its probably unmeasureable.
Emissivity increases the less polished a surface is. An oxidized steel surface has a high emissivity than the same steel body, highly polished. A polished pipe and a black pipe, side by side, the black pipe transfers more heat via radiation than the polished pipe.
It has to do with the wavelength that the radiated heat leaves the surface, I believe. We've only briefly touched it in my current Heat Transfer course.
But real world, I'm not sure the difference is much to speak about. As was stated, it's the convection heat transfer that does the majority of work in the stove-pipe situation.
It has to do with the wavelength that the radiated heat leaves the surface, I believe. We've only briefly touched it in my current Heat Transfer course.
But real world, I'm not sure the difference is much to speak about. As was stated, it's the convection heat transfer that does the majority of work in the stove-pipe situation.
Corie said:
What your educated young backside says is agreed by HotFlame's calculations last season regarding heat given off by a flat black surface.
Give it up guys. The smart ones amoung us say flat black gives off more heat. As Corie says, ya may not notice it but it's more.
Excuse me now. Gotta go cover that new metallic brown paint job on the Sierra with barbeque paint.
Fellas,
Its black body radiation.......the darker the object the faster it will dump heat......via radiation
Its black body radiation.......the darker the object the faster it will dump heat......via radiation
Corie said:
Nope - it's a co-efficient that affects all wavelengths equally (you're thinking of temperature - that skews the emitted wavelengths). Physicists calculate how much light a perfectly emitting object would give off at a given temperature, and then they multiply that by a number between 0 and 1. objects that are black at room temperature are close to 1, objects that are shiny or white are close to 0.
That's because to conserve energy, the best absorbers (those looking black) have to be the best emitters.
a simple demonstration is to take chunk of pipe and drill a small hole in the side. At room temperature, the hole looks darker than the outside. But heat it up, and the whole will be much brighter (you may need to turn the lights off to see it)
mtarbert said:
See. What did I say? All of those three grand Seafoam Hearthstones gotta be spray painted black. And one particular Red Pac Energy Summit that I am thinking of.
It's an energy thing. Do it for your Country.
a little off topic here reflective values of foil faced insulation looses it reflective values in less than a year due to oxidation
Is this the switch grass post I do not mind a little back puffing it has mellowed me out
girls are nice but oh what icing comes with oreos Oreos the very best cockie ever made
guys we are talking about minicule affects
Is this the switch grass post I do not mind a little back puffing it has mellowed me out
girls are nice but oh what icing comes with oreos Oreos the very best cockie ever made
guys we are talking about minicule affects
I agree you are talking peanuts. Now, on the other hand, if we are talking what you might make the surface of solar panels from - then the black counts. But, as Harry mentioned, most of the wavelengths come from inside the pipe and just shine on right through.
Like i said... this is lab stats only. When you start hearing wavelengths and physicists, you know your in trouble. the insides of all this pipe were talking about is black. its just the outside is that is shiney. Unless you are writing your doctorate thesis, it doesnt make one bit of difference. Just fire up the stove and enjoy it .. sheeesh.
Yep , Too much switchgrass , its easy to see .elkimmeg said:
Its O.K. there Elkers , wez gots you back. ( he's getting the munchies now )
DriftWood said:
Yes. A black, rough body (matte finish) will radiate more energy at a given temprature compared to a polished, shiny surface. It will absorb more radiation as well. However, given a particular surface, the amount of heat radiated is strongly dependent on the temprature (fourth power of temprature, to be more precise.)
HotFlame said:
Welcome back HotFlame. Yep it was proven last night. With the non-contact thermo the black pipe on my stove showed 325 degrees while the piece of stainless just above it only registered 180.
Gonna paint that stainless tomorrow.
I also never painted my 316 Ti SS Tee or the liner that shows. Now both are a nice bark red brown black color and no hot paint smell ever.BrotherBart said:
https://www.hearth.com/talk/threads/3106/
Every time I see your burning barrel BrotherBart it reminds me of the year I spent on the picket line at the salt mine.
Below is a brief lesson on radiant heat transfer. References provided. It is a dramatic simplification, since in your chimney, we have convection transfer from the media (flue gasses) to the wall of the pipe. This heats up the pipe to the point that it will then begin external heat transfer, which occurs by conduction, convection and radiation. The only time convection does not apply is when in a vacuum (outer space) or if the pipe is surrounded by media that lock up the air and prevent the molecules from moving (as in packed insulation. Since I'm guessing we are talking about stovepipe, none of these factors apply.
(broken link removed to http://conif.com/HM.html)
Backup reference (with a neat diagram) http://en.wikipedia.org/wiki/Thermal_radiation
RADIANT HEAT TRANSFER
Radiant heat transfer is thermal energy transferred by means of electromagnetic waves or particles.
Thermal Radiation
Radiant heat transfer involves the transfer of heat by electromagnetic radiation that arises due to the temperature of a body. Most energy of this type is in the infra-red region of the electromagnetic spectrum although some of it is in the visible region. The term thermal radiation is frequently used to distinguish this form of electromagnetic radiation from other forms, such as radio waves, x-rays, or gamma rays. The transfer of heat from a fireplace across a room in the line of sight is an example of radiant heat transfer. Radiant heat transfer does not need a medium, such as air or metal, to take place. Any material that has a temperature above absolute zero gives off some radiant energy. When a cloud covers the sun, both its heat and light diminish. This is one of the most familiar examples of heat transfer by thermal radiation.
Black Body Radiation
A body that emits the maximum amount of heat for its absolute temperature is called a black body. Radiant heat transfer rate from a black body to its surroundings can be expressed by the following equation.
Q = б AT^4
where:
Q = heat transfer rate (Btu/hr)
б = Stefan-Boltzman constant (0.174 Btu/hr-ft^2-°R^4)
A = surface area (ft^2)
T = temperature (°R) (unit is in Kelvin)
Two black bodies that radiate toward each other have a net heat flux between them. The net flow rate of heat between them is given by an adaptation of Equation.
Q = б A (T1^4 – T2^4 )
where:
A = surface area of the first body (ft^2)
T1 = temperature of the first body (°R)
T2 = temperature of the second body (°R)
All bodies above absolute zero temperature radiate some heat. The sun and earth both radiate heat toward each other. This seems to violate the Second Law of Thermodynamics, which states that heat cannot flow from a cold body to a hot body. The paradox is resolved by the fact that each body must be in direct line of sight of the other to receive radiation from it. Therefore, whenever the cool body is radiating heat to the hot body, the hot body must also be radiating heat to the cool body. Since the hot body radiates more heat (due to its higher temperature) than the cold body, the net flow of heat is from hot to cold, and the second law is still satisfied.
Emissivity
Real objects do not radiate as much heat as a perfect black body. They radiate less heat than a black body and are called gray bodies. To take into account the fact that real objects are gray bodies, Equation is modified to be of the following form.
Q = Є б A T^4
where:
Є = emissivity of the gray body (dimensionless)
Emissivity is simply a factor by which we multiply the black body heat transfer to take into account that the black body is the ideal case. Emissivity is a dimensionless number and has a maximum value of 1.0.
Radiant Heat Transfer Summary
Black body radiation is the maximum amount of heat that can be transferred from an ideal object.
Emissivity is a measure of the departure of a body from the ideal black body.
Radiation configuration factor takes into account the emittance and relative geometry of two objects.
http://www.infrared-thermography.com/material.htm
Material condition Emissivity
Stainless steel: type 18-8,buffed 0.16
Stainless steel: type 18-8, oxidized at 800°C 0.85
Steel: sheet, nickel plated 0.11
Steel: oxidized 0.79
Long post, but basically it is clear that radiated heat transfer is directly linked to the emisivity value of the stove pipe. Here is the catch: If the stovepipe is bright stainless steel, radiant heat transfer would be greatly reduced, since the emisivity would be low. However, due to the fact that the radiant heat transfer is low, the surface temperature of the pipe will be higher (if measured with a contact thermometer instead of a contactless IR type device, which has to "assume" the surface emissivity), therefore the convection heat transfer will in fact increase (the strength of the convection heat transfer is dependant on the temperature differential between the surface of the pipe and the ambient air. The bigger the temperature differential, the stronger the natural convection that is set up.
Unfortunately, the generally vertical orientation of stove pipes makes it a poor case for efficient convection heat transfer, since the stovepipe is hottest at the bottom and coolest on top. This means that air flow which will rise up the length of the pipe as it is heated will in a short distance reach the temperature of the boundary layer of air around the pipe and no further heat can be absorbed. If the pipe was run horizontally (dumb idea) its potential for convection heating would be much better.
So - bottom line: Stovepipe is black for a reason. Consumers generally don't have the means to measure radiated heat.
(broken link removed to http://conif.com/HM.html)
Backup reference (with a neat diagram) http://en.wikipedia.org/wiki/Thermal_radiation
RADIANT HEAT TRANSFER
Radiant heat transfer is thermal energy transferred by means of electromagnetic waves or particles.
Thermal Radiation
Radiant heat transfer involves the transfer of heat by electromagnetic radiation that arises due to the temperature of a body. Most energy of this type is in the infra-red region of the electromagnetic spectrum although some of it is in the visible region. The term thermal radiation is frequently used to distinguish this form of electromagnetic radiation from other forms, such as radio waves, x-rays, or gamma rays. The transfer of heat from a fireplace across a room in the line of sight is an example of radiant heat transfer. Radiant heat transfer does not need a medium, such as air or metal, to take place. Any material that has a temperature above absolute zero gives off some radiant energy. When a cloud covers the sun, both its heat and light diminish. This is one of the most familiar examples of heat transfer by thermal radiation.
Black Body Radiation
A body that emits the maximum amount of heat for its absolute temperature is called a black body. Radiant heat transfer rate from a black body to its surroundings can be expressed by the following equation.
Q = б AT^4
where:
Q = heat transfer rate (Btu/hr)
б = Stefan-Boltzman constant (0.174 Btu/hr-ft^2-°R^4)
A = surface area (ft^2)
T = temperature (°R) (unit is in Kelvin)
Two black bodies that radiate toward each other have a net heat flux between them. The net flow rate of heat between them is given by an adaptation of Equation.
Q = б A (T1^4 – T2^4 )
where:
A = surface area of the first body (ft^2)
T1 = temperature of the first body (°R)
T2 = temperature of the second body (°R)
All bodies above absolute zero temperature radiate some heat. The sun and earth both radiate heat toward each other. This seems to violate the Second Law of Thermodynamics, which states that heat cannot flow from a cold body to a hot body. The paradox is resolved by the fact that each body must be in direct line of sight of the other to receive radiation from it. Therefore, whenever the cool body is radiating heat to the hot body, the hot body must also be radiating heat to the cool body. Since the hot body radiates more heat (due to its higher temperature) than the cold body, the net flow of heat is from hot to cold, and the second law is still satisfied.
Emissivity
Real objects do not radiate as much heat as a perfect black body. They radiate less heat than a black body and are called gray bodies. To take into account the fact that real objects are gray bodies, Equation is modified to be of the following form.
Q = Є б A T^4
where:
Є = emissivity of the gray body (dimensionless)
Emissivity is simply a factor by which we multiply the black body heat transfer to take into account that the black body is the ideal case. Emissivity is a dimensionless number and has a maximum value of 1.0.
Radiant Heat Transfer Summary
Black body radiation is the maximum amount of heat that can be transferred from an ideal object.
Emissivity is a measure of the departure of a body from the ideal black body.
Radiation configuration factor takes into account the emittance and relative geometry of two objects.
http://www.infrared-thermography.com/material.htm
Material condition Emissivity
Stainless steel: type 18-8,buffed 0.16
Stainless steel: type 18-8, oxidized at 800°C 0.85
Steel: sheet, nickel plated 0.11
Steel: oxidized 0.79
Long post, but basically it is clear that radiated heat transfer is directly linked to the emisivity value of the stove pipe. Here is the catch: If the stovepipe is bright stainless steel, radiant heat transfer would be greatly reduced, since the emisivity would be low. However, due to the fact that the radiant heat transfer is low, the surface temperature of the pipe will be higher (if measured with a contact thermometer instead of a contactless IR type device, which has to "assume" the surface emissivity), therefore the convection heat transfer will in fact increase (the strength of the convection heat transfer is dependant on the temperature differential between the surface of the pipe and the ambient air. The bigger the temperature differential, the stronger the natural convection that is set up.
Unfortunately, the generally vertical orientation of stove pipes makes it a poor case for efficient convection heat transfer, since the stovepipe is hottest at the bottom and coolest on top. This means that air flow which will rise up the length of the pipe as it is heated will in a short distance reach the temperature of the boundary layer of air around the pipe and no further heat can be absorbed. If the pipe was run horizontally (dumb idea) its potential for convection heating would be much better.
So - bottom line: Stovepipe is black for a reason. Consumers generally don't have the means to measure radiated heat.
I was waiting for KeithO to weigh in on this - I wasn't disappointed.
I do have to take exception to the last line, though - consumers do indeed have a way to measure infrared radiation. I for one have a calibrated backside, and I can easily tell the difference between a black stovepipe and a shiny stainless stovepipe!
Seriously, there are great experiments to demonstrate the point. Sit ten feet or so from a fire with your eyes closed. You can easily tell when someone walks between you and the fire. That's radiation, not convection.
Face an outside non low-e window on a cold night. Have someone hold a large sheet of aluminum foil between you and the window. Again, you can tell with your eyes closed.
I do have to take exception to the last line, though - consumers do indeed have a way to measure infrared radiation. I for one have a calibrated backside, and I can easily tell the difference between a black stovepipe and a shiny stainless stovepipe!
Seriously, there are great experiments to demonstrate the point. Sit ten feet or so from a fire with your eyes closed. You can easily tell when someone walks between you and the fire. That's radiation, not convection.
Face an outside non low-e window on a cold night. Have someone hold a large sheet of aluminum foil between you and the window. Again, you can tell with your eyes closed.
Nofossil, I didn't mean "sense" radiated heat, I meant measure, at least in a repeatable way. There was a lovely discussion on NPR at lunchtime about chefs who maintained that there was some chemically undefined substance that resulted from cooking in certain ways. This was disputed by scientists who were unable to find any difference in the chemical composition of the food. After years and years of investigation, scientists finally discovered that humans have a 5th taste receptor on the tongue and named it after the descriptor coined by a Japanese chemist who had maintained and supported the theories of the french chefs. The name: Umami. The whole article is here: http://www.npr.org/templates/story/story.php?storyId=15819485
RADIANT HEAT TRANSFER nice post KeithO. I will do the math. I shoved your post into wiki. You should edit and post in wiki
https://www.hearth.com/econtent/index.php/wiki/Stainless_Steel/
https://www.hearth.com/econtent/index.php/wiki/Stainless_Steel/
- Status
Similar threads
