In reply to RC Macaulay's message of Thu, 02 Dec 2004 15:11:47 -0600: Hi, [snip] >nightime temp of 70 degrees F. The water temperature inside the olla will fall >to 70 degrees F as it "surrenders " heat to the clay wall of the olla. >Comparing the differential potential for giving up heat to atmospheric >conditions external to the olla is usually explained via evaporation due to >the breeze. There is NO breeze in the desert. The lowering of the olla water >temperature must be caused by what?
It is caused by evaporation. Even without wind, the thin layer of air against the wall of the vessel will be saturated with water vapour, which makes it lighter than the surrounding air. That makes it rise up, and it gets replaced by heavier dryer air, which in turn absorbs more moisture from the vessel. So this works, even in the complete absence of wind. However even on so called wind still days, there are usually occasional small air movements, which help out with the process. >The indians dont worry about it.. they just enjoy the fact. > >Now consider a 12" X 12" X 1" Mexican Saltillo tile , red clay with small >amounts of volcanic and flint rock. After firing the tile, it is extremely >dry. Keep the tile dry but allow it to completely cool and sprinkle a small >amout of water on the tile and watch it " boil" as it is absorbed into the >porous tile. Why does the water momentarily boil? This "boiling" is more likely to be air bubbling up through the water, as the water soaks into the porous tile, and replaces the internal air. [snip] Regards, Robin van Spaandonk All SPAM goes in the trash unread.
