Fyndium
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Temp diff between stillhead and boiler?
What is the relationship between temp of vapor on stillhead compared to boiler temp? I've faced this same thing multitude of times when the boiler
temp can be much higher than the vapor temp. Meanwhile, reducing the boiler temp will cause vapor production to cease and temp quickly stop. For
example when stripping off toluene, the boiler temp can be 130C and stillhead sits at 110 (and oil bath temp can be 160+C), but if heating is ceased
even momentarily, vapor production quickly depletes to zero.
For some stuff it is apparent like sulfuric acid which boils at 337, but the vapors generated to very high temps remain at 100 being water.
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teodor
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Obviously vapours are cooled down climbing higher in your system. I believe the difference is dependent on temp difference with the air in the lab and
thermal insulation.
But even with perfect insulation you have condensation inside the system which creates the temp difference, look how a fractionating column works.
[Edited on 2-12-2020 by teodor]
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Fulmen
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First: What's your setup? And what are you actually measuring? Is the boiler sensor calibrated and placed so it measures the temperature of the
boiling liquid?
We're not banging rocks together here. We know how to put a man back together.
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Fyndium
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I use glass thermoprobes on boiler(3 neck) and stillhead with ground joints. They have a little of paraffin oil on bottom for thermoprobe. The
thermoprobes are not calibrated against anything scientific, but I've got 5 of them and they all show up expected numbers in same conditions (known bp
liquids like acetone, water, ethanol, toluene, etc) so I expect them to be of decent accuracy.
The boiler probe is immersed within the liquid, and the stillhead probe sits close to the takeoff to condenser. I also use third probe for bath (and
other probes for aux stuff like coolant, etc).
The setup is common distillation setup. Bath is of silicon oil, heated with induction. It does not affect the probes, unless they are placed directly
on top of it while operating and they will mess up completely at once when that happens.
https://www.sciencemadness.org/whisper/files.php?pid=644977&...
The probes are presented in this setup, I've just upgraded it after this pic by purchasing more thermowells and shortening the stillhead one to match
the takeoff length.
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teodor
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+ pressure difference. The main factor, by the way, in the case of pure (one component) liquid which has the same temp. of boiling and condensation.
The difference is dependent on the boiling speed and the channel size. Condensation in the channel also can contribute to this difference.
[Edited on 3-12-2020 by teodor]
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