Which region is associated with the formation of a vapor film that insulates the surface?

Which region is associated with the formation of a vapor film that insulates the surface?

• A. Natural Convection
• B. Nucleate Boiling
• C. Transition Boiling
• D. Film Boiling

Answer: (D)

When the surface gets very hot, a continuous vapor layer forms between the surface and the liquid. This vapor film insulates the surface because vapor conducts heat far less effectively than liquid, so the heat transfer drops and the surface temperature rises. This regime is distinct from natural convection (no boiling), and from nucleate boiling (bubbles form and depart, which enhances heat transfer). It’s also the unstable transition between nucleate boiling and film boiling, where heat transfer deteriorates before the vapor film becomes fully established.

When the surface gets very hot, a continuous vapor layer forms between the surface and the liquid. This vapor film insulates the surface because vapor conducts heat far less effectively than liquid, so the heat transfer drops and the surface temperature rises. This regime is distinct from natural convection (no boiling), and from nucleate boiling (bubbles form and depart, which enhances heat transfer). It’s also the unstable transition between nucleate boiling and film boiling, where heat transfer deteriorates before the vapor film becomes fully established.