The forms of heat transfer are traditionally described as conduction, convection, and radiation. Is evaporation (or any other change of state) counted as one of those forms? Or is it considered its own distinct form of heat transfer?
[Physics] Conduction, convection, radiation: Does evaporation count as one of those
convectionevaporationheat conductionthermal-radiationthermodynamics
Best Answer
In engineering, heat transfer covers various mechanisms, including thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes (e.g. evaporation).
At a given pressure, different boiling regimes exist depending on temperature (the following image applies to water at a pressure of 1 atm).
In particular, the nucleate boiling regime is important in engineering (e.g. for the design of nuclear reactors) because of the high heat flux at small temperature differences. In this regime, isolated steam bubbles form at the hot surface, separate from the hot surface, and may condense again somewhere else in the subcooled liquid. Thus, in addition to the heat transfer by convection, the steam bubbles carry away heat in form of their enthalpy of vaporization $\Delta H_\mathrm{vap}$ which is released again when the bubbles condense. Furthermore, the movement of steam bubbles increases the movement of the liquid, thus increasing the heat transfer by convection.
(Note that if too much steam is generated at the hot surface, the steam insulates the hot surface from the liquid, thus strongly decreasing the heat flux after reaching the critical heat flux.)