On Sat, Jul 19, 2003 at 08:12:06PM -0400, Robert J. Chassell wrote: > Hmmm.... you are right that the temperature is often more or less > constant 2 meters or so underground. However, in my understanding, > dirt and rock are very good insulators, and that heat flows slowly > through them.
Dirt is a good thermal conductor compared to air, as I said. > What is the heat conductivity of dirt, rock, and nickle-iron? Does > anyone one know? Dirt and rock are similar, in the range 0.2 - 2 W / m K. Iron is about 84 W / m K Nickel is 92 W / m K air at 300K is 0.026 W / m K > I think it is misleading to speak of them, even metaphorically, as the > `north and south poles' since people think of the poles of earth as > being cold. Please rephrase my statement about the equator in less misleading terms, and I will be glad to use them. They are the best I can think of (actually, I copied it from Clarke) > Or are you meaning colder in the sense that the parts of the end caps > that are closer to the axis take their surface temperatures from the > air at that distance from the central axis, and those temperatures are > colder than the `surface' (i.e., rim) temperature? The heat capacity of the endcaps is much more than the air, so it is better to say that the air is affected by the temperature of the endcaps. Since dirt and rock are better thermal conductors than air, the temperature of the endcaps should vary less with radius than the temperature of the air at the equator varies with radius. The variation of the temperature of the air with radius near the endcaps is hard to predict without a simulation, because there will be some heat transfer from the endcaps to the air. > What are the weather implications of having a region with less light > input than another? You would set up some convective air currents. > > Due to endcap effect, the temperature will also vary along the > length of the habitat. > > Is that really the case? Isn't that a question to be determined? I > would expect the opposite: that with sufficiently good insulation, the > surface of the end caps would come to the same temperature as the air > fairly quickly and would neither contribute nor take much heat from > the air. Same temperature as which air? The air on the axis is colder than the air at the rim. If the endcap had the same temperature vs. radius profile as the air, then there would be heat flowing from the rim to the center of the endcaps (heat flows from high to low T), and the center would heat up until in equilibrium the endcaps are at the same temperature as the rim. Then the endcap is hotter than the air on the axis, so the air on the axis will be heated by the endcap. > By the way, from personal experience I can tell you that as a general > rule on a sunny day, air tends to rise over fields and sink over > forests. Yup, my personal experience coincides with that. The best thermals I found were often over dirt and especially blacktop or stone. I think that is just because the sun heats those areas to a higher temperature than a forest (presumably the trees/leaves dissipate the heat much better than the dirt). -- "Erik Reuter" <[EMAIL PROTECTED]> http://www.erikreuter.net/ _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
