The thermal efficiency of an ideal cycle is much higher than that of an actual cycle. Why?
The correct answer and explanation is:
The thermal efficiency of an ideal cycle is much higher than that of an actual cycle due to several reasons related to the inherent limitations in real-world engines and processes.
An ideal thermodynamic cycle, such as the Carnot cycle, assumes that all processes are reversible and there are no losses due to friction, heat dissipation, or other irreversibilities. This means that energy is converted from heat into work without any energy being wasted. The Carnot cycle also operates between two heat reservoirs at constant temperatures, ensuring that the working fluid undergoes idealized processes, such as isothermal expansion and compression, and adiabatic expansion and compression. These ideal conditions maximize the energy extraction from the heat source, resulting in the highest possible efficiency for a given temperature difference.
In contrast, actual cycles in real-world engines, such as the Rankine or Brayton cycles, experience numerous inefficiencies. For example, heat losses occur at various stages of the cycle due to imperfect insulation, friction within mechanical parts, and the non-ideal behavior of working fluids. Additionally, real engines suffer from irreversibilities like turbulence, heat transfer resistance, and incomplete combustion, all of which lead to wasted energy.
Furthermore, in practical systems, the working fluids are not in a state of perfect thermodynamic equilibrium, and they may undergo processes that deviate from the idealized paths assumed in theoretical cycles. These losses contribute to a reduction in the overall efficiency of the cycle. As a result, the efficiency of actual cycles is always less than the theoretical maximum predicted by an ideal cycle, making the real-world performance less than that of an idealized, frictionless, and perfectly reversible process.