Cy, Not coming from a Physicists but here's some rules old and new. Learned during solar panel research for my home back in the last century (1994) cutty & paste or from that era more like Cutty Sark. Armchair analysis...tranduce not amplify GerryC Wein's Law: Wave length is inversely proportional to temperature of the source. The relationship of the wavelength of maximum intensity of a black body to its absolute temperature is expressed by Wein's law. Wein's Law L max = a/T a = 2898 if L is measured in microns Also: Kirchhoff's Law: emissivity = absorbtance at any given wavelength and temperature Thus "a good absorber is a good emitter" (which has to be true for the object to stay at the same temperature) This can be expanded into the "common sense" equation that the total incident energy must equal the sum of the absorbed, reflected, and transmitted energy. Energy = energy absorbed + energy reflected + energy transmitted Kirchhoff's law is really just common sense: When radiant energy hits any particular material it has to do one of three things: 1) Be absorbed (a perfect black body with emissivity of 1 absorbes all the radiant energy) 2) Be reflected (the opposite of a perfect black body - a material with low emissivity) 3) Pass through the material (transparancy) The energy of the raditaion absorbed, reflected and transmitted through the material must equal the energy hitting the material. Finally: Stephan-Boltzman Law: Radiant energy is proportional to the fourth power of the absolute temperature of the source. The amount of radiation produced by a perfect radiator is expressed by the Stephan-Boltzman Law, where: For ordinary objects, non-perfect radiators, Q is reduced by multiplication of the object's emissive power (always less than one). And emissivity changes with temperature. But, for the most part, the amount of radiatiant energy is a function of the fourth pawer of the absolute temperature of the source of radiation. Thus, at normal temperatures the amount of infra-red radiation produced by an object is relatively low, but as the temperature is increased, radiation increases significantly. Stephan-Boltzman Law gives the total energy emitted, but as the temperature rises, more of the energy is emitted at shorter wavelengths as given by Wein's Displacement Law and shown by the Planck blackbody curves.. Thus, if you double the absolute temperature, you get 2 to the 4th or 16 times the TOTAL energy out, but more of this energy is output at shorter wavelengths and may not be felt as heat. (We normally consider the 8 to 12 micron region as thermal infrared) - Hoffamn. For example: An object at 80 deg.F (540 deg. absolute temperature Rankin) with an emissive power of 0.85 will produce 124 BTUH/sq.ft. When its absolute temperature is doubled to 1080 deg. (540 deg.F which is about the temperature of a very hot glass door) its output is increased sixteen fold to 1,984 BTUH/sq.ft. If its absolute temperature is quadrupled to 2160 deg. (1,620 deg.F which is not a very hot wood fire) its output increases two hundred and fifty six fold to 31,744 BTUH/sq.ft. An open fire radiates at about 16 times more energy than the same fire would produce behind glass doors. From: cy at shusterpiano.com To: caut at ptg.org Date: Tue, 30 Jun 2009 08:53:47 -0600 Subject: Re: [CAUT] FW: Re: crack Yes, but does it *amplify* the heat, or merely *transduce* it? Physicists want to know! (grin) --Cy-- Cy Shuster, RPT ABQ, NM www.shusterpiano.com Radiant heat is essentially low frequency light. The space blanket will help. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut.php/attachments/20090630/18d7e53a/attachment.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC