thanks for the data. of course RFG could not get through a big piece of metal, but low frequency magnetic field could pass through, if the metal is not too ferromagnetic, and cause induction current in a resistive ferromagnetic nickel powder (but also in the metal around...)...
but your explanation is very good... they choose the usual basic solution for this kind of problem of "hot metal"... and as I say nothing seems to evocate something else resistive and chemical heating... all seems simple, except - the catalyst - the startup chemical heating - maybe a tricky control method... 2012/1/24 Robert Lynn <[email protected]> > No such thing as a magnetically transparent steel (or any conductor for > that matter) RF will not pass through a conductive material. And for the > same reason high frequency magnetic fields will not penetrate any metal by > more than a fraction of a mm. For a bit of a guide as to what sort of > distances we are talking about check out the skin effect > http://en.wikipedia.org/wiki/Skin_effect (not exactly the same, but > similar behaviour). > > If you are referring to a non-ferromagnetic steel and what significance it > might have then keep in mind that Austenitic Stainless steels like AISI > 301, 304, 316, 321 etc are the cheapest, most commonly available materials > with good high temperature strength, creep resistance, ductility, excellent > machinability, excellent weldability, resistance to hydrogen embrittlement > and resistance to many other forms of chemical attack and oxidation. They > are used in many high temp applications for all of those reasons, and are > in many ways the chemical (and particularly food processing) industry's > work horse materials. I am sure that there is nothing more to the use of > non-ferromagnetic stainless steel than convenience. You can also get > Ferritic stainless steel (4xx series) that are ferromagnetic (ie attracted > to magnetic fields), but generally not as good for high temps or corrosion. > > > > On 24 January 2012 17:42, Alain Sepeda <[email protected]> wrote: > >> >> Being fast to start and avoiding meltdown mean that they have a very >> good, nearly optimal control. >> Maybe part of the secret is classic control theory, helping to design the >> optimal retro-action, once you know the core thermal parameters... >> >> but being also able to work without cooling, with "nudist" reactors under >> the sky, mean they don't need the coolant to survive... >> something is stabilizing the core, or at least helping/damping the core >> to be stabilized from far by a very good temp->power loop (maybe a good PID >> predictor). >> >> One idea would be that they use very fast induction heating, but they say >> NO RFG... maybe induction is not RFG for them (true in a way). >> this might explain why they use (as someone explain here) a magnetically >> transparent steel. >> the stability of the core might be about the powder behavior at high >> temperature, relative to induction... (why not curie point? 627 C?) >> but in their spec they talk about resistors, not induction coils... >> they talk about a chemically assisted preheating... undisclosed. >> pre-heat 6 seconds... max op temp 1050C... >> >> however coolant oil is limited to 350C, and 430 for molten salts... not >> the 600C we see as limit for the tests... >> >> whatever they did, it is smart job... either a tricky intrinsic feedback >> (like lead-bismuth nuke do), or optimal control, after good modelization. >> >> >> >> 2012/1/24 David Roberson <[email protected]> >> >>> The design of the DGT device allows them to lower if not stop the >>> coolant flow into the heated core unit. The heating of the core can then >>> be much faster and also require less net energy than Rossi's >>> configuration. I would expect that both designs would need approximately >>> the same temperature for efficient output. This is just my opinion, but I >>> think the DGT design is more ideal. >>> >>> Dave >>> >> >> >
