Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Arves on October 29, 2021, 10:38:20 AM
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Hi,
I hope that my questions fits in here.
I am looking into dewpoint on nitrogen, and specific liquid nitrogen (LIN). I understand that nitrogen gas that comes from liquid form will have a different dewpoint than nitrogen gas that have not been liquid?
Perhaps some could help explain why there is a difference, and also what the dewpoint for both will be at atmospheric pressure.
Any help is much appreciated!
Best regards,
Arve
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Sounds a bit off to me, dew point is not a property of a gas (other than water vapor).
Perhaps you are asking about boiling temperature (which is the same as condensation temp)?
Even then it should not be different for liquid and gaseous phases.
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Hi, thanks for responding
From google it says that: Bottled nitrogen is often specified as dryer than 2 ppm (parts per million) equivalent to a dewpoint of -94F (-70°C). However, someone told me that when the nitrogen has previously been in liquid form, the dewpoint will be affected. And that instead of 70°C, it will be around 60°C as a result of the previous liquid state.
This is kind of what I am trying to get confirmed or denied.
Note that have very little knowledge on this.
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The dew point is the minimum temperature to which a gas (usually air) can be cooled before water in the gas (usually air) condenses. As the temperature is cooled, the water carrying capacity of the gas decreases (relative humidity - the amount of water in a gas divided by the maximum amount it can carry - increases). Eventually the amount of water vapor in the gas reaches the maximum amount the gas can hold (relative humidity = 100%). Any further reduction in temperature causes the water vapor to condense. The dew point is mostly a function of the water vapor concentration and the temperature. The history of a gas doesn't seem to me as though it would matter to the dewpoint, unless the history affects the water content. As an example, suppose that nitrogen gas has x% of water content, which would impart a certain dew point y. If liquification of the nitrogen followed by de-liquification causes the water content to be different, then the dew point of the nitrogen will also be different for the previously liquidifed nitrogen. I guess one could envision a scenario where liquification of nitrogen causes its water content to
rise lower slightly. In which case the de-liquified nitrogen would then have a lower dew point because it has a higher lower water content. Whether this is generally true of previously liquified nitrogen, I have no idea.
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It would have a higher dewpoint if the water content was higher.
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Sorry, you are right, thanks for the correction. I fixed the post.