gracies
At 12:02 22/04/02 +0200, heu escrit: >A les 09:31 22/04/02 +0200, Xavier m'has escrit, >>Sincerament, com diuen en Castella �Han oido campanas y no saben donde�. > >Passa't per (l'enlla� ja el va passar un internauta ahir o abans d'ahir) >http://howthingswork.virginia.edu/microwave_ovens.html >mira la pregunta >" Why does water react in a violent and dangerous way when overheated in a >microwave oven? CA " >i mira el video (a partir del 13 experiment... a veure si ho trobes >normal....�s bastant explicatiu, per molt que tiri la forquilla dins del >got l'aigua normalment no salta d'aquesta forma) >http://howthingswork.virginia.edu/movies/shw28k.rm > >El que diuen all�, (almenys el que jo he ent�s) �s que si el recipent que >cont� l'aigua no t� cap (o prous) impureses o rugositats (cosa que passa >amb el vidre), aleshores no hi ha cap lloc a on es poguin comen�ar a formar >les bombolles, i per tant l'aigua es va """sobreescalfant""" fins que entra >amb contacte amb alguna cosa que li "permet" crear les bombolles, per� com >que ja est� tan calenta en lloc de fer bombolletes en fa una de moooolt gran >* e * >-------------------------------- >" Why does water react in a violent and dangerous way when overheated in a >microwave oven? CA " >Water doesn't always boil when it is heated above its normal boiling >temperature (100 �C or 212 �F). The only thing that is certain is that >above that temperature, a steam bubble that forms inside the body of the >liquid will be able to withstand the crushing effects of atmospheric >pressure. If no bubbles form, then boiling will simply remain a >possibility, not a reality. Something has to trigger the formation of steam >bubbles, a process known as "nucleation." If there is no nucleation of >steam bubbles, there will be no boiling and therefore no effective limit to >how hot the water can become. > >Nucleation usually occurs at hot spots during stovetop cooking or at >defects in the surfaces of cooking vessels. Glass containers have few or no >such defects. When you cook water in a smooth glass container, using a >microwave oven, it is quite possible that there will be no nucleation on >the walls of the container and the water will superheat. This situation >becomes even worse if the top surface of the water is "sealed" by a thin >layer of oil or fat so that evaporation can't occur, either. Superheated >water is extremely dangerous and people have been severely injured by such >water. All it takes is some trigger to create the first bubble- a fork or >spoon opening up the inner surface of the water or striking the bottom of >the container-and an explosion follows. I recently filmed such explosions >in my own microwave (low-quality movie (749KB), medium-quality movie >(5.5MB)), or high- quality movie (16.2MB)). As you'll hear in my flustered >remarks after "Experiment 13," I was a bit shaken up by the ferocity of the >explosion I had triggered, despite every expectation that it would occur. >After that surprise, you'll notice that I became much more concerned about >yanking my hand out of the oven before the fork reached the water. I >recommend against trying this dangerous experiment, but if you must, be >extremely careful and don't superheat more than a few ounces of water. You >can easily get burned or worse. For a reader's story about a burn he >received from superheated water in a microwave, touch here. > >-------------------------L'INTERNAUTA------------------------------- >Per enviar missatges a la llista: <mailto:[EMAIL PROTECTED]> >Altes, baixes i informaci� de la llista: <http://www.internauta.net> >-------------------------------------------------------------------- > > -------------------------L'INTERNAUTA------------------------------- Per enviar missatges a la llista: <mailto:[EMAIL PROTECTED]> Altes, baixes i informaci� de la llista: <http://www.internauta.net> --------------------------------------------------------------------
