"Gilligan" wrote in message
. ..
http://en.wikipedia.org/wiki/Boiling



Boiling is the rapid vaporization of a liquid, which typically occurs when
a liquid is heated to a temperature such that its vapor pressure is above
that of the surroundings, such as air pressure. Thus, a liquid may also
boil when the pressure of the surrounding atmosphere is sufficiently
reduced, such as the use of a vacuum pump or at high altitudes. Boiling
occurs in three characteristic stages, which are nucleate, transition and
film boiling. These stages generally take place from low to high surface
temperatures, respectively.

Nucleate boiling is characterized by the incipience and growth of bubbles
on a heated surface, which rise from discrete points on a surface, whose
temperature is only slightly above the liquid's saturation temperature. In
general, the number of nucleation sites are increased by an increasing
surface temperature. An irregular surface of the boiling vessel (i.e.
increased surface roughness) can create additional nucleation sites, while
an exceptionally smooth surface (such as glass) lends itself to
superheating.

When the surface temperature reaches a maximum value, the critical
superheat, vapor begins to form faster than liquid can reach the surface.
Thus, the heated surface suddenly becomes covered with a vapor layer.
Because of the vapor layer's lower thermal conductivity, this vapor layer
insulates the surface. This condition of a vapor film insulating the
surface from the liquid characterizes film boiling.

Transition boiling may be defined as the unstable boiling, which occurs at
surface temperatures between the maximum attainable in nucleate and the
minimum attainable in film boiling.

The propeller is the thing that makes the boat go, innit?

Max