On 4/18/07, Peter P. wrote: > Mike Harrison whitewing.co.uk> writes: > > >... cheap transformer > > In fact the transformer is built to saturate and thus limit power transfer to > the magnetron (and also to limit heater current when this is cold). The > magnetron is a current driven device (it can be modelled like a giant zener > diode in its operating area). > > But the bottom line is that one can only put a 500 Watt heater into a cup of > water with difficulty. Thermal tubes ? Is not so difficult as you may believe. One test we have done here is that there isn't a semnificative efficiency difference between a heating system using natural gases and water as thermal fluid and a microwave heating system using microwave and water... Ditto smaller things. Therefore microwave heating is the > most efficient for small (portion sized) food items when all factors are > accounted for. A normal heater (electric plate) will have a lot more losses and > waste the heat used to heat itself (its own mass) when used cyclically. Peter, you have generaly right. The answer I have expected was that microwaves are heating the food directly proportional with the permitivity of the food. The absorbtion inside the food is not homogenous, even the microwave oven producers are putting some large effort in homogenizer systems. If you can measure the field density into a microwave oven I'm sure you'll understand what I'm saying. The anodic current of an 800W magnetron is about 500 to 600 mA and the anodic voltage is around 4KV (in fact is the cathodic voltage because the anode is connected to ground) I have designed and manufactured in the past ten years many microwave controlled generators used for Microwave Assisted Organic Sintesys on small probes as 1ml (and as low temperatures as 0C...40C with a temperature controling precision inside the reactor chamber of about 0.1C ) http://incdtim.netfirms.com/procesare_dinamica.html (sorry just the picture is written in english, but you don't need it) or industrial microwave owens: http://www.geocities.com/vsurducan/electro/micro/micro.htm The most interesting thing about microwaves is that heating is just a colateral fenomena...and definitely not the most important. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist