Describe the different regimes of boiling heat transfer and their characteristics.

Pool boiling has distinct regimes as wall superheat increases: Natural convection (ΔT<5°C, no bubbles), Nucleate boiling (ΔT=5-30°C, bubbles form at nucleation sites, very high heat transfer up to 1 MW/m²), Transition boiling (unstable, vapor film forms and collapses), and Film boiling (stable vapor layer insulates surface, much lower heat transfer). The Critical Heat Flux (CHF) occurs at peak nucleate boiling; exceeding it causes rapid temperature rise (burnout). Design must maintain nucleate boiling regime. Condensation modes: filmwise (lower h, ~5000-25000 W/m²-K) vs dropwise (higher h but difficult to maintain).