What is the temperature of the pot itself (the metal container) when filled with water and placed over a stove until the water boils?
Is it limited by the boiling of water? Only if it is super thin?
How does this mesh with the classic experiment of putting a flame under a water balloon?
WAG (I don’t take Heat Transfer until next semester…!)
Assuming standard temperature and pressure, with the water at 100C, the pot would be at 100C on the inside surface that touches the water, and would be slightly colder on the outside surface or areas away from the water (rim, lid). The amount that it would be colder would be dictated by the ambient air temperature, the thickness/distance of the material from the water, and it’s heat coefficient. Metal conducts heat fairly well, so it would be very close to 100C, I would think.
I do not have the knowledge to actually sketch this out and solve an example problem, but I’m putting this answer up anyways to see whether or not I’m right!
It occurs to me that I’m not taking into account the heat from the burner…I don’t know how hot that would be and how that would be distributed through the pot and the water. A large amount of that energy would be going into maintaining the boiling water, but some would also be heating the metal. So the pot is exposed to three temperatures: 100C, Ambient air and burner temp.
Clearly someone else needs to step in and answer this!
I would hate to see an equation that could handle everything.
I do know that the metal can be quite a bit hotter than the water. Here’s an experiment that works on my stove (a pretty typical gas burner affair). Put cold water in a pot and put them on the stove for a while without stirring. Wait until the water is hot, but not boiling (say 120-140, like you would want for coffee and tea). At that point, grab the handle and swirl the pot so that water sloshes partway up the metal sides. Using my pans and stove, the sloshing water will immediately sizzle on the sides. So I know the metal sides of the pot are well above 212, even when I know the water in the pot is only 140 or so.
It may be hard to get a perfect measure of the pot’s temp, but you can use an oil/candy thermometer and set it up so that it touches the bottom of the pot. Anyone who does frying or candy making knows you never let the thermometer touch the bottom precisely because you get readings that are hotter than the liquid.
It is certainly limited by the boiling of water in the sense that if and when the water boils away, the temperature of the pot will increase dramatically.
I’d call it reasonably obvious that the temperature of the bottom of the pan, in contact with heating element or flame, is significantly higher than the temperature of the boiling water.
Ok, so the temperature of the pot is higher than the temperature of boiling water (dracoi’s experiment shows it clearly) but it is somewhat limited by the boiling of the water as evidenced by what happens when you boil a pot dry (my mom did this with a double bottom pot and the bottom came off and burned her very seriously).
What happens in a tall pot (say your typical pasta pot) at the point where the surface of the water is?. I guess that the temperature is hotter at the bottom and decreases with height, but what at that point? Does it begin to rise again? Is the point just under the surface of the water the coldest point on the pot? Is that at 212oF (or whatever it is for your location) or still hotter?
How does the material and its gauge affect all this? I am guessing that a paper thin copper pot keeps closer to the temperature of boiling water than a heavy iron cauldron, right?
You can’t define “the temperature of the pot”, since different parts will be at different temperatures. How much variation of temperature you can get, and how it would be distributed through the pot, would depend on unknowns like the composition of the pot, its shape, the thickness of the metal, and what and where the heat source is.
The metal is being cooled by the water. Thr outside skin of the pot at the bottom is the hotest. heat is being transfered by conduction both through the metal and up the sides. The outside of the pot will be at a higher temp than the inside. As the heat travels up the sides it also travels through the pot to the water inside and is radiated out to the air. If the flame is high enough and enough heat is transfered to the pot it can travel up the sides of the pot to the top. On the out side the temp will be lower as you travel away from the heat source. Above the water line the outside temp will not be higher than below the water line. The inside may be hotter because it is not being cooled by the water.
Water flow through a boiler is critical. If there is no water in contact with the boiler tubes to “cool” them then they can fail.
Radiation has little to do with the transfer of thermal energy from pot to water to air - very much the most important aspect of this is the phase transition from liquid to gas (i.e. the creation of steam).