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Post by satamax on May 30, 2015 21:06:53 GMT -8
Hi everybody.
Does anybody know a way to calculate or estimate the power shed by a surface of bare metal, for a certain difference in temperature?
We use barrel size, and bell size. What i would kike to be able to estimate, is, what bare metal surface is needed to heat a room without overheating it, and be able to store more heat in the heat storage.
Any idea?
Thanks.
Max.
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Deleted
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Post by Deleted on May 31, 2015 5:17:53 GMT -8
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Post by satamax on May 31, 2015 9:10:16 GMT -8
Thanks a lot Karl.
I will realy have to delve into that, because my physics aren't up to par at all!
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Post by Robert on Jun 12, 2015 11:19:37 GMT -8
Thanx Karl. I have some question... Got confused a little bit... since in some places it shows that clay has emmisivity of 0.39 And the red brick - 0.93 In other places they show that clay has higher values... What i want to ask is what material for the masonry heater will work best? I mean radiate maximum energy... Usually i like to plaster my stoves with clay... and now i got confused... if i will plaster my stove with clay, am i loosing a radiation power compaed to brick? I am really wondering how to find what is the best and most efficient and most healthy for people... somewhere i read that clay radiated the Far Infrared wave, very similar to that freq of a human... therefore i got super excited, since i like clay very much... but now when i read about emmisivity it confuses me... looks like that not the material that the stove is made of is more important than the coating of that heater... So how it will be when we will have coating made of: 1. red brick 2. clay plaster 3. Ceramic tiles with glazing? Can you elaborate on that Karl please? Thank you robert
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Deleted
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Post by Deleted on Jun 13, 2015 3:08:57 GMT -8
Steel may well have a higher emissivity than clay. The surface has more influence than the material. Emissivity depends heavily on condition and structure of the surface, as it is actually a function of the real emitting surface area and less a function of the material. Chemical or mechanical aging greatly increases the surface area. An aged, worn, scratched or rough surface has thus a much higher emissivity than a smooth or even polished surface, regardless of the material. Artistically inclined people may increase the surface area with ornaments or engravings. Simply mixing some coarse particles into any paint or clay finish will certainly help too. For example: www.engineeringtoolbox.com/emissivity-coefficients-d_447.htmlSteel Oxidized 0.79 Steel Polished 0.07 Stainless Steel, weathered 0.85 Stainless Steel, polished 0.075 Stainless Steel, type 301 0.54 - 0.63 Steel Galvanized Old 0.88 Steel Galvanized New 0.23 Make the surface large enough by ornaments and engravings and even polished gold will throw a lot energy. With respect to a house: One can save a surprising amount of energy by using a smooth plaster instead of a rough plaster, as the real emitting surface may be less than half.
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Post by pyrophile on Jul 12, 2015 2:33:58 GMT -8
To Karl "With respect to a house" : do you mean for an outside plaster, I suppose?
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Post by patamos on Jul 12, 2015 10:31:54 GMT -8
And does the rougher surface also increase absorptivity? If so we will do well to keep the insides of our bells somewhat rough, and might achieve net gain on exterior house plasters that have solar gain.
On this note, friends who built a cob house a few years back put many thermal sensors in their rough plastered walls. They were surprised to discover how much heat the wall absorbed from winter sun. Even when the air temp was -4c the walls with sun on them got up to 30c at their outside surface. This effectively reversed the thermal transfer through the wall's mass, making for r-100 for at least part of the time. This 'mass enhanced U-value' offered a net gain over all...
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Post by JesCar on Nov 2, 2016 18:01:48 GMT -8
I built a cast-core rocket stove (heater) and used a 20 Gal. barrel over the heat riser. My exhaust gas temps were around 120-135 F. Then I found a 20 Gal. metal Galvanized trash can and used it as the Bell. To my surprise, my exhaust temp. went to 220 F+. Thinking that I had the "Baked potato in tinfoil" thing going on, I took my propane torch and burned the galvanize off until it turned gray in about an 8 inch circle at the upper side of the bell. When I checked the temp. with my infrared gun it showed approx. 185 F. Knowing that it should be hotter then that, I took some high temp. black paint and painted about half of the gray circle. When I checked the black half of the circle it showed about 350 F. when I moved the temp gun a few inches back to the gray, it went back to 185 F. When I held my hand near the bell I could feel strong energy by the black, less by the gray and much less by the shiny Galvanize. I burned out the galvanized can and painted it black, put it back on my stove and my exhaust temps. were back to there normal range. Question... Does my temp. gun only read the infrared energy passing through the steel can??
JesCar
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jrl
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Post by jrl on Dec 9, 2016 6:50:30 GMT -8
I built a cast-core rocket stove (heater) and used a 20 Gal. barrel over the heat riser. My exhaust gas temps were around 120-135 F. Then I found a 20 Gal. metal Galvanized trash can and used it as the Bell. To my surprise, my exhaust temp. went to 220 F+. Thinking that I had the "Baked potato in tinfoil" thing going on, I took my propane torch and burned the galvanize off until it turned gray in about an 8 inch circle at the upper side of the bell. When I checked the temp. with my infrared gun it showed approx. 185 F. Knowing that it should be hotter then that, I took some high temp. black paint and painted about half of the gray circle. When I checked the black half of the circle it showed about 350 F. when I moved the temp gun a few inches back to the gray, it went back to 185 F. When I held my hand near the bell I could feel strong energy by the black, less by the gray and much less by the shiny Galvanize. I burned out the galvanized can and painted it black, put it back on my stove and my exhaust temps. were back to there normal range. Question... Does my temp. gun only read the infrared energy passing through the steel can?? JesCar My guess is that the reflectivity of the galvanized metal was bouncing the temp gun's laser back at you. By painting it you gave it a matt finish which stopped reflecting the laser.
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Post by Dave A. on Dec 15, 2016 19:59:57 GMT -8
The infrared thermometer is more accurate when directed to a black surface. Metals reflect different values depending on reflectivity. Technicians typically paint or tape pipe surfaces black for greater accuracy.
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stoker
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Post by stoker on Feb 1, 2018 16:07:40 GMT -8
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Post by Orange on Feb 2, 2018 5:59:04 GMT -8
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kkp
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Post by kkp on Jul 13, 2018 17:05:03 GMT -8
Flat black paint, of nearly any type, comes in at .94+.
Concerning the shiney copper (emissivity: approx .05) that I have for my secondary air supply, perhaps a coat of some rustoleum high temp spray paint on the bottom facing into the airway would work out. That's what I'll be trying anyway.
Cu2O and Cu2O - coppers two oxides, have pretty high rating also. I could chemically oxidize the bottom if the paint burns off.
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