Final answer:
The characteristic regime where heat flux increases with the temperature of the heating element despite film formation, indicating a phase change to film boiling, is a precursor to 'film boiling'.
Step-by-step explanation:
When boiling a saturated liquid, there is a characteristic regime where the heat flux increases with the temperature of the heating element despite film formation. This unique characteristic is a precursor to film boiling. During film boiling, a layer of vapor forms between the heating surface and the liquid which acts as an insulating layer, leading to much lower heat transfer coefficients. As a result, the temperature of the heating surface must be significantly higher than the boiling temperature of the liquid to maintain heat transfer.
Nucleate boiling occurs before film boiling and is an efficient heat transfer mode where vapor bubbles form at nucleation sites on the heating surface. When the heat flux increases beyond the critical point, the bubbles coalesce to form a film, marking the transition to film boiling. As the surface temperature rises significantly above the boiling point of the liquid, the risk of burnout (damage to the heating surface due to excessive heat) also increases.