On Jun 26, 2009, at 6:17 PM, Ron Nossaman wrote: > Huh? > > What heating system besides radiant (like a fireplace, say) heats > objects to higher than air temperature? A coil heated thermal mass > of concrete is a throm wall, heated from inside, rather than by > radiant energy of the sun. It heats the air around it. I know from a > lifetime of personal experience that the air right next to a large > force heated mass is considerably warmer than anything else in the > room. > > I'm quite aware of the intent of the discussion as it relates to > pianos. I was attempting to clear up some basic physics issues for > anyone who might be willing to listen, not to argue with everyone > who isn't. > > Ron N Huh, indeed. Any heat source radiates heat. A heat source may be active (fire, chemical reaction, for instance, something that creates heat), or passive (an object hotter than its surrounds, a cup of hot coffee). When the heat source is in a liquid or gaseous medium, movement of heat occurs via convection. Parts of the liquid or gaseous medium become hotter than other parts, and the heat energy causes them to be more mobile (and usually expand), creating movement within the medium and mixing of warmer and colder portions. Gravity enters the picture, as the expanded medium is less dense, hence "moves upward" away from the center of gravity, and that is a major cause of the mixing. But regardless of this action of gas and liquid medium, and the degree to which heat is absorbed by the medium, heat is also radiated from the heat source in the form of infrared rays. Every heating system relies on a radiant component. Some systems rely more heavily than others on convection for the distribution of heat, say to warm all the air in a room. Radiant floor heating and radiant floorboard heating are examples. Can they, via radiation of heat, cause solid objects to become hotter than the average ambient air temperature in a room? Yes, they can. Granted, the air particles closest to the source are likely to be hotter than the air particles at a distance, and so a solid physical object might or might not become hotter than certain small portions of the total air in the room. But any object that is impacted by the heat radiated from a heat source will "absorb heat" based on its physical properties and the intensity of the heat source. Something relatively close to a heat source will usually become hotter than the average temperature of the air in a room. Because of radiation. There is no difference whatsoever between a fireplace and a radiator (or radiant heated floor) in terms of "being radiant" or not, except for the actual temperature and heat output of that heat source. If your radiant floor were as hot as your fireplace, it would radiate just as much. If your fire in the fireplace were able to be as little hot as the water in the coils, it would radiate that little. There is no such thing as a convection heater. Convection doesn't heat, it just mixes temperatures of the medium. There is such a thing as distribution of heat by convection. But you have to start with a radiant source. I am just trying to make clear some basic physics issues for anyone interested, not arguing with anybody <G>. Regards, Fred Sturm University of New Mexico fssturm at unm.edu
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