RogueRose
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What temp is considered super heated steam and what materials will withstand these conditions?
I'm trying to figure out is a 10 bar vessel (180C/357F) would be considered super heated steam, and if steam of that temp would rapidly degrade
iron/steel. I need to find a material that can handle this temp in both a containment vessel (~1-1.5L) as well as tubing that can carry the steam
from the vessel into a turbine system. I'm also looking at something that will allow for the 180C to be further heated as a couple coils (maybe 3-5ft
long) are passed through a hot fire (1500-2000F) to further increase the temp after it leaves the vessel. In this case it would most likely be used
to pass over hot carbon, not run into a turbine - though I'd like to test that was well and see if there is significant increase in power output.
I'm leaning towards 304/316 SS for the vessel (appropriate thickness) with a blow-off valve (brass OK?), and then the same material for the tubing
(probably 3/16" - 3/8" ID) or if possible some thick walled copper if it is strong enough to handle the pressure and IDK if hot steam degrades copper
the same as it does iron/steel.
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Twospoons
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I would try to use the same material throughout, no matter what you choose, otherwise galvanic corrosion may be a big problem , unless you select
materials carefully.
Espresso machines operate in the vicinity of your stated conditions : https://www.wholelattelove.com/blogs/articles/espresso-machi...
SS is probably your best bet, so long as there's no chlorine/choride in the water.
[Edited on 9-10-2019 by Twospoons]
Helicopter: "helico" -> spiral, "pter" -> with wings
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Vomaturge
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In the case of steam, superheated means the temperature is greater than the boiling point of water at a given pressure. 180C and 10 atm is close to
saturation, so probably not superheated. Also, I don't think e.g. 180C steam at 5 atmospheres would be more corrosive than 300C steam at 90 atm,
simply because the former was "superheated" and the latter was not.
I'd say you could use normal carbon/mild steel pipe, or even copper at 180C, (although soldered joints may start having problems at temperature). For
the 800C superheater, stainless steel and realize its strength will be a half to a quarter of what it is at room temperature
For either setup, assume there will be a few catastrophic failures, due to engineering flaws temperature/pressure excursions, etc. before you get it
running smoothly. Be safe and have fun.
PS why is espresso brewed at high pressure? Is it to enable liquid water at ~200C, or is it just part of forcing the water to flow through the grinds?
The espresso websites talk about final (in the cup) temp, pressure while brewing, but not brewing temperature.
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Yttrium2
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I think it's to move the water through the grinds
Good question!
I wonder how pressure cooker coffee would taste, it might be the next best thing!
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Ubya
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maybe you misread, espresso machines have never used steam at 180°C.
coffee grounds would char at that temperature.
maybe you read 200° F as 200°C
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Twospoons
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I was referring to the pressure. Coffee is ideally brewed at 95C. But there are also single tank espresso machines that heat the tank to ~120 to 130C
for steaming milk. So not exactly the same conditions, but a similar sort of engineering problem.
Helicopter: "helico" -> spiral, "pter" -> with wings
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rockyit98
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aluminium would do fine up to 350 Celsius it can handle the pressure.
do careful research about stainless steel type. this old tony
https://www.youtube.com/user/featony
"A mind is a terrible thing to lose"-Meisner
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Metacelsus
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Wouldn't chemical reactivity with 350 °C steam be an issue? I don't think the surface oxide layer would be stable under those conditions.
[Edited on 2019-10-10 by Metacelsus]
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andy1988
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You may enjoy this read on boiler corrosion, and perhaps similar material.
A great discussion here on creating a magnetite layer.
Also a good read on magnetite.
[Edited on 10-10-2019 by andy1988]
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