A liquid that stays liquid at 200C and is not inherently expensive or toxic would be needed for heating. The system for the liquid is closed, but made
out of pressure tubing that can withstand about 10Bar of pressure, so the liquid should not boil. Would food oils do how in this process? The purpose
is heat transfer and buffer that can withhold the pressure inside the heated system at 200C steady.Lambda-Eyde - 20-12-2012 at 19:41
Ethylene glycol (antifreeze) ?madcedar - 21-12-2012 at 15:19
Silicone oil might do it but it's probably much easier for go for a vegetable oil.
Also a low melting point metal like Wood's metal (http://en.wikipedia.org/wiki/Wood's_metal) may be suitable?
[Edited on 21-12-2012 by madcedar]kristofvagyok - 21-12-2012 at 15:27
Silicone oil is the best choice.
Vegetable oil is for eating and not for chemistry, always keep it in mind. Also the Wood's metal is a bad idea it's toxic as hell, expensive and it
get's easily oxidized, it is not funny to work with. I have made it once in my life and I could say that it was enough, I don't want to mess with it
again.Oscilllator - 21-12-2012 at 18:13
There are non-toxic low melting point alloys, but they're very expensive, and I don't see whats wrong with using cooking oil
[Edited on 22-12-2012 by Oscilllator]bbartlog - 21-12-2012 at 18:48
I'd worry about the longer term stability of cooking oil in such a system. Ethylene glycol seems like a good choice to me; silicone oil is kind of
expensive.Oscilllator - 21-12-2012 at 20:04
I'd worry about the longer term stability of cooking oil in such a system. Ethylene glycol seems like a good choice to me; silicone oil is kind of
expensive.
"long term" as in over a period of more than 1 run? If so, than you could just replace it, since cooking oil is fairly cheap (a good source of vast
quantities of cooking oil is used oil from restaurants, although it would have a fair few impurities)chucknorris - 21-12-2012 at 20:25
Well, the mantle volume is over 200 liters and it should run for thousands of hours non-stop, so silicone oil is everything but good choice in terms
of price. Problem with liquid metals is the density-price ratio: tin, lead and lead-bismuth alloy costs a few € per kg, but you need 11 of them in
one liter, so that's just about some 2.5 tons of the stuff.bbartlog - 22-12-2012 at 09:31
Those metals are also not liquid at room temperature... even if your unit runs thousands of hours continuously, the use of a heat transfer material
that solidifies on shutdown really complicates your design. Also, just in terms of calories of heat moved per unit mass pumped, molten metal is pretty
poor.
Glycerine and propylene glycol are other polyols that might be good choices. Propylene glycol is less toxic than ethylene glycol and has a slightly
higher specific heat. Glycerine has a higher boiling point, is also non-toxic, and isn't too expensive ($450 or maybe less for a 55 gallon drum, which
sounds like about the volume you'd need).
