Basically how boiling takes place?
Also like to know…
What makes boiling point alter at various altitudes?
Why bubbles rise through boiling water?
[Physics] What makes water boil
phase-transitionthermodynamicswater
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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.
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.
Boiling will occur when the equilibrium vapor pressure at the temperature of the liquid is equal to the total pressure of the system and heat is being provided (either externally, or by the sensible heat of the liquid itself). The gas phase in contact with the liquid can be comprised of pure vapor (in which case the total pressure is essentially equal to the equilibrium vapor pressure), or, it can be comprised of a mixture of vapor and air (in which case the total pressure essentially equal to the sum of the equilibrium vapor pressure of the boiling substance plus the partial pressure of the air).
At 40 C, it is still possible for water to boil in a container if the gas is evacuated to a pressure below the equilibrium vapor pressure at 40 C (a non-equilibrium situation). Boiling can continue until the total pressure in the head space rises to a value equal to the equilibrium vapor pressure. As long as the partial pressure of the substance in the vapor and the total pressure (if air is present) is less than the equilibrium vapor pressure of water at the liquid temperature, boiling will continue. The heat of vaporization can be supplied by the liquid itself, so the water temperature will be dropping (assuming heat is not being directly supplied). Once the equilibrium vapor pressure at the liquid temperature falls below the total pressure, boiling will stop. Once the partial pressure of the vapor in the gas phase becomes equal to the equilibrium vapor pressure, evaporation will stop.
With regard to the question about the melting point and the triple point, the melting point is very close to the triple point. At the triple point, pure water is present in all three phases (no air present in the gas phase) and the total pressure is equal to the equilibrium vapor pressure of the liquid and solid. At the melting point, air is present in the gas phase at 1 atm., and the total pressure of the system is thus essentially 1 atm. The difference between the melting point and the triple point is only about 0.01 C.
Best Answer
I'll give somewhat satisfying answer...
Heat - We know that Heat is a form of energy that is transferred by difference in temperature of regions. Here, it's just the amount of energy required by the $H_2O$ molecules in the liquid state to get converted to gaseous state. As we provide heat, it gets absorbed by water to get converted into water vapors.
Convection - It's the transfer of heat through water (proper term is fluid) caused by molecular motion. You see, Convection can be brought to focus by taking normal experiments into account. Particles (even Chalk) would rise and fall in somewhat rotatory motion due to this flow of heat. The water vapor formed at the bottom of the liquid (water) flows to the top in the form of united water vapor bubbles. 'Cause it's a gas and its so hot down there..! (This explains bubble formation when water is boiled.)
Now, why boiling point differ with altitude:
The atmospheric vapor pressure is 1 atm only for us (I mean, at sea level). For higher elevations, the pressure is too low out there in atmosphere. It should also be noticed that the volume change is too high when a liquid changes to gas.
By Ideal gas equation, For 'n' moles of gas $\implies$ $P=\frac{nRT}{V}$ which shows that pressure is inversely proportional to volume. So, we could relate this expansion with pressure. Expanding against low pressure takes somewhat lower energy than expanding against high pressure. And hence the boiling point would be low at higher altitudes. Wiki says it somewhat clearly with a formula.
Using this water boiling point calculator, Boiling point at sea level (1 atm or 29.92 inches of Hg) is approximately 212 °F whereas at a height of about 5000 ft. (24.9 inches of Hg), it is 203 °F.