1. Definition

Definition taken from standard NF ISO 3977

"Thermodynamic system comprising two or more power cycles, each of which uses a different working fluid. Combined steam/air cycles (the most commonly used working fluids) have increased thermal efficiency because the two cycles are thermodynamically complementary: the heat rejected by the gas turbine (Brayton cycle) is at such a temperature that it can be the main energy source or a complementary energy source for the steam turbine (Rankine cycle).