  Boiling is a very efficient way to transfer heat from a heater to the liquid
carrier. We discuss the boiling crisis, a transition between two regimes of
boiling: nucleate and film boiling. The boiling crisis results in a sharp
decrease in the heat transfer rate, which can cause a major accident in
industrial heat exchangers. In this communication, we present a physical model
of the boiling crisis based on the vapor recoil effect. Under the action of the
vapor recoil the gas bubbles begin to spread over the heater thus forming a
germ for the vapor film. The vapor recoil force not only causes its spreading,
it also creates a strong adhesion to the heater that prevents the bubble
departure, thus favoring the further spreading. Near the liquid-gas critical
point, the bubble growth is very slow and allows the kinetics of the bubble
spreading to be observed. Since the surface tension is very small in this
regime, only microgravity conditions can preserve a convex bubble shape. In the
experiments both in the Mir space station and in the magnetic levitation
facility, we directly observed an increase of the apparent contact angle and
spreading of the dry spot under the bubble. Numerical simulations of the
thermally controlled bubble growth show this vapor recoil effect too thus
confirming our model of the boiling crisis.
