Ideal Brayton Cycle – Detailed Explanation

Thermodynamics Concept – Ideal Brayton Cycle

Question:

The ideal Brayton cycle consists of which set of thermodynamic processes?

☐ Two isochoric and two isobaric processes
☐ Two isobaric and two isothermal processes
☐ Two isothermal and two isentropic processes
✅ Two isentropic and two isobaric processes

Answer and Detailed Explanation:

The ideal Brayton cycle is a fundamental model for modern gas turbine engines. It comprises four main thermodynamic processes involving a working gas (usually air):

🔸 Step 1: Isentropic Compression (Process 1 → 2)

Air enters a compressor and undergoes a reversible adiabatic compression (no heat exchange), which is called an isentropic process.

P increases, V decreases, T increases (no heat exchange, entropy constant)

🔸 Step 2: Isobaric Heat Addition (Process 2 → 3)

The high-pressure air enters a combustion chamber where heat is added at constant pressure. This represents an isobaric process.

P = constant, T increases, V increases

🔸 Step 3: Isentropic Expansion (Process 3 → 4)

The high-energy air expands through a turbine, undergoing a second isentropic process. This expansion produces useful work.

P decreases, V increases, T decreases (entropy remains constant)

🔸 Step 4: Isobaric Heat Rejection (Process 4 → 1)

At the end of the cycle, heat is rejected to the surroundings at constant pressure. This brings the system back to its initial state.

P = constant, T decreases, V decreases

✅ Correct Answer: The ideal Brayton cycle consists of two isentropic and two isobaric processes.

This cycle is widely used to model jet engines, gas turbines, and is essential in understanding modern thermodynamic power systems.

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