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Steam evolved during pressurized experiment

by alfa rat
Tags: parr, pressure, steam
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alfa rat
#1
Jun4-14, 05:59 PM
P: 1
I'm developing an experiment where an exothermic reaction will evolve water as an unavoidable byproduct, and for containment purposes I'll be using a sealed 25cc steel reaction vessel for initial testing. The question I'm posting here is for the purposes of safety and control, acknowledging fully that there is some risk involved and that nobody responding here will be held responsible for what happens.

The question is: How do I determine how much pressure will be produced within the container as the steam forms from the reactants? The steam tables I'm familiar with are geared more for piping transport and work than for containment problems like this one. I'm specifically interested in arriving at a maximum upper limit for steam which will not rupture the container, and from there allowing a 20% safety margin below that for a safe maximum yield. The reaction is expected to take place at around 650 C. It would be helpful if someone could direct me to the math so that if the project increases in scale we can compensate appropriately.
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Simon Bridge
#2
Jun4-14, 09:58 PM
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Back of envelope - you have a certain amount of steam and a certain amount of water, and some other stuff.
You know the densities and the temperatures for these and you should have some idea of how they change or how much to expect of each.

The impact of liquid water, very roughly, is to occupy some volume - reducing the volume available to steam and other gasses ... the pressure exerted on the sides of the container is about the pressure exerted by the gasses. So you want some gas equations. It can get as complicated as you like with partial pressures.

There are other details, but that should give you an idea.

JIC: I take it you will include a pressure valve, so steam is released before the vessel explodes.
25cc is not very big though.

It is impossible to advise you precisely because we don't know what you are attempting.
russ_watters
#3
Jun4-14, 10:42 PM
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Wow. These are fairly basic thermodynamics questions and the danger in making a pressure vessel with little understanding of what you are doing is enormous (for one thing, you cannot do this without a safety relief valve on the vessel and a permit - it is actually illegal). You're making a bomb and we can't support that here, your release from liability doesn't really help that.

You need to team up with/hire an expert to work on this project with you. The risk is just too great for us to try to help you. Thread closed.


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