Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thermal Tumbler and unusual noise...

  1. Aug 12, 2017 #1
    Back in... man... probably 1996 I went to work with a thermal tumbler filled with some hot beverage or another. I settled in and took a swig; the liquid was good and hot and I kind of marveled at how well the tumbler worked and how it was nice to have a warm drink in my cool environment and after a chilly ride in to work.

    As it sat, sealed, on my workbench, it started to make a noise; a high pitched squeal. I was intrigued by that., and the discussion that ensued after pointing it out to a co-worker and my boss has always been vexing. I see both sides of this argument.

    My take was that like any sealed vessel with a higher internal temperature, the pressure in the vessel would be higher than the cooler outside pressure, thus the tumbler was effectively venting the pressure which was greater than the seals could, well, seal. The differential was greater due to the cool work environment than it would have been inside my home which was quite a bit warmer. In short, I thought gasses were escaping due to being forced out as the pressure inside the tumbler was higher than the external pressure.

    My boss disagreed. His position was that the noise was created by air rushing into the tumbler. His theory was that the liquid was cooling, and so the pressure was dropping at which point regardless of the cooler air outside, it would rush into seals at a matter of a vacuum state developing.

    In retrospect I'd say both instances are true based on pressure and temperature changes over time. I suspect that initially the tumbler was purging excess pressure, but at some point this is reversed and the tumbler then starts to draw in atmosphere. I think this is observable when putting a bowl filled with water and covered in plastic wrap in a microwave. Initially the plastic remains flat with room temperature water. Once the water is heated, the wrap expands with the increasing pressure due to the liquid heating enough to create water vapor which then expands. But, as the heating cycle ends, the plastic wrap then shrinks downward and meets the surface of the water, effectively vacuum sealing itself.

    What are your thoughts on this?
    Last edited by a moderator: Aug 12, 2017
  2. jcsd
  3. Aug 12, 2017 #2
    Let's say that the water temperature is 70 degrees C. You open the thermos pour some out and replacing that volume with dry air, then you seal it up again.

    So the cold dry air is at 1 atmosphere, 0 psi guage. Now the water in the thermos begins to evaporate adding to that pressure as it mixes with the dry air. The partial pressure of water vapor at 70 degrees C will be 233.7 torr, 0.3075 atmospheres, 4.5 psi. More over, the cool air will now heat up to about 70C, so it will also increase its partial pressure. So it will vent out.

    And, yes, given enough time, the partial pressures will reach equilibrium and begin to cool off - perhaps dropping the pressure in the thermos to less than 1 atmosphere.
  4. Aug 12, 2017 #3
    Interesting response. The air volume in the tumbler to begin with was very small, and only one sip had been taken. I doubt the air was all that dry since even pouring the hot liquid into the tumbler will create condensation; steam is released as you pour. To that end I'd suggest that evaporative effects would be extremely limited. With that, what is your modified assessment?
  5. Aug 13, 2017 #4
    It's only a matter of degree (no pun intended).
    Before the vessel was resealed, it was open to the air and to convective circulation and cooling. The steam you saw was evidence of this. Warm moist air is less dense that cool dry air (yes, moisture makes air less dense). So as the moist air met the room air, it condensed and appeared as visible steam.

    When sealed, the air in the thermos may still have been warm and moist, but not at equilibrium with the thermos environment.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted