I was just cooking some noodles and staring at the pot waiting for them to cook made me wonder… Will my food cook quicker when the water is boiling and bubbling, or when it is at a temperature where it is about to start boiling but there are no bubbles in the water yet?
My instinct would be that food will cook quicker just before the water starts boiling because steam conducts heat slower than water and so when the food is in contact with the steam bubbles it receives less thermal energy. I'm basing this assumption off the fact that a steam bath/Turkish bath which is AFAIK at 70 degrees C and close to 100% relative humidity feels a lot colder than sticking my finger in a cup of water at 70 C. Although this begs another question, does the food even come in contact with the steam or does the desire of the bubble to stay round (minimum energy configuration) actually prevent it from even coming in contact with the actual food?
And what is it that intrinsically makes one substance a better thermal conductor than another? I mean what is heat anyways–I was always taught that it was the "kinetic energy of the particles", so are we talking $0.5mv^2 + 0.5I\omega^2$ where $m$ is the mass of the individual atom? If so, what is the relationship that equates this to degrees Kelvin? And even then, that makes sense for a gas, but what about a liquid or a solid where particles are not free to move around like they can in a gas, is it potential elastic energy of the particles displacing from the optimum minimum energy lattice configuration?
Best Answer
This is absolutely the opposite of reality! A steam bubble in contact with a body with a temperature less than 100°C will condense on this body, transferring about 540 cal/g! In fact heating a wall by condensing steam is one of the most efficient heat transfer methods.
But now your primary question: those noodles "cook" faster where they experience the higher temperature. In a pot on a fire, the surface of the water will be as low as maybe 80 or 90 degrees, when bubbles raise at the bottom, but do not reach the surface yet. (Again here: heat transfer by bubble evaporation is extremely fast, same reasons as for condensation) 10 or 20 °C less are a lot when cooking noodles (wheat starch) this may lower the reaction rate to half the value at 100°C, or even lower (rule of thumb for such reaction).
Thermal conductivity: most amorphous solids/liquids have similar, low heat conduction. Crystalline solids are medium, metals are much higher, the thermal conductivity being related to the electrical conductivity. Google for: Wiedemann Franz Lorenz. Thermal conductivity of gases can be calculated using kinetic gas theory, this was "triumph" for Clausius, Maxwell and Boltzmann.