Closed-Cycle Gas Turbine – Ideal Compressor Process In an ideal closed-cycle gas turbine (Brayton cycle), the compressor process is modeled as isentropic (adiabatic and reversible).

Introduction / Context:
Cycle modeling requires selecting ideal processes for major components. The Brayton compressor is ideally isentropic, providing a benchmark for defining isentropic efficiency and comparing to real polytropic compression behavior.

Given Data / Assumptions:

• Closed Brayton loop with compressor, heater, turbine, and cooler.
• Idealizations: adiabatic, reversible compression and expansion.
• Working fluid approximated as an ideal gas with nearly constant properties.

Concept / Approach:

An isentropic compressor minimizes required work for a given pressure ratio in the ideal limit. Real compressors are polytropic with efficiencies less than 100%, but the isentropic model is the reference used in performance calculations and definitions (e.g., eta_c = isentropic work / actual work).

Step-by-Step Solution:

Verification / Alternative check:

T-s diagrams show vertical (constant entropy) lines for ideal compression/expansion. Real data deviate rightward due to irreversibilities.

Why Other Options Are Wrong:

Isothermal compression is not Brayton ideal; 'polytropic' describes real behavior but not the ideal assumption; 'none' and 'isobaric' are incorrect for a compressor.

Common Pitfalls:

Using isentropic relations outside their validity (large property variation); confusing stage polytropic efficiency with overall isentropic efficiency.

Final Answer:

isentropically