Closed vs. open Brayton cycles – efficiency trend Compared with an open-cycle gas turbine, a closed-cycle gas turbine generally delivers __________ thermal efficiency (for similar component efficiencies and pressure ratios).

Introduction / Context:
Gas turbines can operate in open cycles (air in, exhaust out) or closed cycles (working fluid recirculates through external heat exchangers). The architecture affects recuperation potential, pressure losses, and temperature control, influencing overall efficiency.

Given Data / Assumptions:

• Comparable pressure ratio and component efficiencies are assumed.
• Closed cycle allows effective heat recovery via recuperators and has controlled working-fluid properties (e.g., helium, air, CO2).
• Pressure losses on the intake/exhaust (open cycle) are not present in the same way for a closed loop.

Concept / Approach:
Closed cycles commonly incorporate high-effectiveness recuperation using stable mass flow and controlled temperatures, raising the average temperature of heat addition and lowering that of heat rejection relative to the open cycle. Thus, the thermal efficiency tends to be higher for similar hardware efficiencies.

Step-by-Step Solution:
Compare heat-addition profiles: closed cycle uses external heaters and recuperators to preheat the working fluid before main heating.Recognize reduced stack/exhaust losses in closed loops.Conclude higher efficiency for closed Brayton configurations under similar design constraints.

Verification / Alternative check:
Textbook Brayton-with-recuperation analyses show that recuperation increases thermal efficiency, and closed cycles facilitate high recuperator effectiveness due to consistent, clean working fluids.

Why Other Options Are Wrong:

• “Lower” and “same” contradict well-known recuperated closed-cycle results.
• “Depends only on fuel” is false—cycle efficiency is primarily thermodynamic, not fuel dependent.
• “Zero” is nonsensical.

Common Pitfalls:
Confusing closed-cycle recuperation advantages with combined-cycle improvements; they are different concepts.

Final Answer:
higher