Explain the concept of regeneration in thermodynamic cycles.

Regeneration is a technique to improve cycle efficiency by recovering heat from exhaust or leaving streams to preheat incoming fluids. In Rankine cycle, feedwater heaters use extracted steam to preheat boiler feedwater. In Brayton cycle, a regenerator transfers heat from turbine exhaust to compressed air before combustion. This reduces external heat input required, improving thermal efficiency. Regeneration is most effective when there is large temperature difference between exhaust and inlet streams.