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Index of Subjects Hi Steve & All, No my mill is powered entirely by upward flow of warm air; a thin circular sheet of brass clipped to form eight vanes which slope downward to the left. This fan consequently turns near side to the left. (Clockwise viewed from above). The original unit, made in Sweden, was powered by candles and intended as a Christmas table decoration. The fan is supported by a brass plate with three arms on each of which an angel hangs and a brass rod hanging from each angel rings a chime as it turns. I just stuck the working parts in a support made from a length of burned out oven element, bent to be stable with the filling removed from the vertical end by tapping. Just to confuse matters; note that what we call clockwise (down on the right side) is counterclockwise from the clock's viewpoint. YT, Dave W. On 5/26/2020 5:53 PM, Stephen Shaw wrote: > Hi Dave, > I’m not familiar with your named device or its principle of operation, but we too have a small windmill that simply rests on top of our (also black) wood stove and spins faster as the stove heats up. It works as a Peltier device, with parallel hot and cold junctions built into a short aluminium tower, the top of which is an air-cooled heat sink. I think it cost ~$130 some years ago. The ‘hot' side of the Peltier junction faces down to the hot stove top upon which the frame rests, while the ‘cold' side is uppermost, and its heat sink is cooled partly by the little rotating fan and partly by radiation. With enough heating differential, the Peltier effect generates a small current which is enough to turn a small DC motor that carries the fan. > > Is this like your device? If so, you may have simply have cleaned and in effect flattened the stove top a bit so the base of the device makes better thermal contact with the Al base of the windmill, though the black-body improvement should help a bit. A better solution in my case and maybe yours would be to apply a thin layer of heat-sink compound to the base of the tower. This is a messy paste based on zinc oxide, used standard in electronics to attach a power transistor to an aluminium or copper heat sink, while at the same time providing electrical insulation. It would certainly enhance heat conduction to our windmill, but the compound is white, sticky and difficult to remove once applied: I would become locally unpopular if I so disfigured our black stove top, so I haven’t yet risked the experiment. > Steve > > On May 25, 2020, at 7:55 PM, David Webster <dwebster@glinx.com> wrote: >> Dear All, >> >> I heat the house mostly with wood burned in a fireplace insert and, >> apart from some air circulation in under the fire box, up behind it and >> out over the top, most heating is radiant off of the top. >> >> For decades I have used a Swedish Christmas heat mill, sold for >> candles, which I adapted for stove top use, as a measure of heat release >> rate. In recent decades it turned less frequently and for several years >> not turned at all even with a brisk fire so I suspected wear and >> increased friction at pivot points. >> >> The stove top had become dull grey in color so to improve >> appearance I located a source of blacking last fall but it could be >> applied only to a cold stove so was applied to the top, on first recent >> warm morning this spring, and the increase in heat radiation from the >> top was dramatic. With just a token fire that Swedish heat mill was >> spinning full tilt ! >> >> This I assume was a practical demonstration of increased radiation >> from a black surface (Black Body Radiation ?). And all along I had >> imagined that stove blacking was just for appearance. >> >> Yt, DW, Kentville >> >>
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