Physics Asked by Cat on September 26, 2020
As far as I know solids exchange heat energy on contact the best of the three states, due to density and etc. while gasses are worst at that.
Recently I found out that, when boiling eggs, it is not necessary for them to be immersed in water. An alternative is to pour a small amount of water into the pot, put the eggs in and heat the pot so that the water turns into steam and heats up the inside of the pot and the eggs, thus cooking them.
In this approach you save the time needed to heat a full pot of water, which is a lot, but at the same time I was wondering how much longer does it take for the steam to transfer heat to the eggs, compared to water heated to the same (or relatively the same) temperature (since the water makes better contact with them and should transfer more heat, being a solid).
The control parameter is the convection coefficient $h$ between the eggs surface and the water (or steam).
The rate of heat transfer is $q = hA(T_m - T_e)$ where $A$ is the surface area, $T_e$ is the surface temperature of the egg and $T_m$ the temperature of the medium (liquid water of steam).
The advantage for steam is the possibility to reach higher temperatures, so $(T_m - T_e)$ can be bigger. But in my opinion it is far less important than the difference of $h$, much greater for liquid water.
As an example (of cooling instead of heating), a half inch steel rebar can be quenched to increase its mechanical properties after a rolling mill. The coolant is a turbulent flow of water, and the average temperature drops from $1000^circ C$ to $600^circ C$ in about 1 second. There is no chance to get a rate like that with a cold air flow.
Answered by Claudio Saspinski on September 26, 2020
since your cooker is covered , the heat can not escape. As long, as the eggs have not reached 100°C at the outside, the water vapor condenses on the eggshell and transfers so the condensing heat, wich is more than boiling water could transfer.
Answered by trula on September 26, 2020
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