1) Pool boiling occurs when a heater is submerged in a pool of initially stagnant liquid.
2) When the surface temperature of the heater exceeds the saturation temperature of the liquid by a sufficient amount, vapor bubbles nucleate on the heater surface.
3) The bubbles grow rapidly in the superheated liquid layer next to the surface until they depart and move out into the bulk liquid. While rising as the result of buoyancy, they either collapse or continue their growth, depending on whether the liquid is locally subcooled or superheated.
4) Nucleation is a molecular-scale process in which a small bubble (nucleus) of a size just in excess of the thermodynamic equilibrium is formed.
5)Initial growth from the nucleation size is controlled by inertia and surface tension effects.
The growth rate is small at first but increases with bubble size as the surface tension effects become less significant.
6) When the growth process reaches the asymptotic stage, it is controlled
by the rate of heat transferred from the surrounding liquid to facilitate the evaporation
at the bubble interface.
7) If the bubble, during its growth, contacts the subcooled liquid, it may collapse.
8) The controlling phenomena for the collapse process are much the same as for the growth process but are encountered in reverse order.
By Rajendra
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