Closed-Cycle Gas Turbine – Cooling in the Cooler (Heat Rejection) In a closed Brayton (closed-cycle gas turbine), the working fluid is cooled at essentially constant pressure in the cooler/heat exchanger before returning to the compressor.

Introduction / Context:
Closed-cycle gas turbines recirculate a working fluid (often helium, nitrogen, or air). Understanding where heat is added and rejected and under what idealized conditions is crucial for modeling performance and sizing heat exchangers.

Given Data / Assumptions:

• Closed Brayton loop with compressor, heater, turbine, and cooler.
• Pressure drops in heat exchangers are neglected in the ideal model.
• Steady-state, steady-flow operation.

Concept / Approach:

The ideal Brayton (open or closed) has two constant-pressure heat-transfer processes: heat addition in the heater/combustor and heat rejection in the cooler. The other two processes (across compressor and turbine) are ideally isentropic. Therefore, the cooler removes heat at nearly constant pressure, returning the fluid to the compressor inlet state along the low-pressure line of the p-v or T-s diagram.

Step-by-Step Solution:

Verification / Alternative check:

T-s diagrams of the Brayton cycle show horizontal lines (isobars) during heat addition and rejection. Small real pressure losses do not change the fundamental classification.

Why Other Options Are Wrong:

Constant volume applies to Otto/Stirling isochores; constant temperature is for Carnot/Stirling isotherms; 'none' is incorrect given the standard Brayton idealization.

Common Pitfalls:

Confusing open vs. closed cycles; assuming exhaust to atmosphere implies open cycle (closed cycles reject heat in a cooler, not to free atmosphere directly).

Final Answer:

constant pressure