0
$\begingroup$

Most teapots have vent holes to let steam out (and also to let air in when pouring the tea, but this is irrelevant to this question).

If the vent hole is blocked, pressure starts building up in the teapot and:

  1. either it pushes steam out of the nozzle, or,
  2. if the water level is above the nozzle entrance, it pushes water out.

(Side remark: case 2 accidentally happens to my chinese teapot when a thin film of liquid water forms over the vent, and it makes a mess if I'm not watching. I hate it!)

My question is: what is causing the pressure buildup? The pot is cooling, so if it only contained an ideal gas, pressure would go down. Is this related to the phase change rate of the hot water? What equations describe the phenomenon?

$\endgroup$
4
$\begingroup$

The pot is cooling, so if it only contained an ideal gas, pressure would go down.

The pot may be cooling but the hot tea inside heats up the initially cold air (ambient temperature) in the teapot. Consider air to be a near-ideal gas then the Ideal Gas Law applies, so:

$$pV=nRT$$

The heating air in an enclosed space causes a slight pressure build-up and that is what you are observing and what is causing the nuisance when the venting hole is sealed off.

See also my very related answer, here.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.