Effect of reheating on the compressor side in a multistage gas turbine: how does reheating during expansion influence compressor work?

Introduction / Context:
Reheating in gas turbines inserts heat between turbine expansion stages to increase turbine specific work (and often to maintain blade metal temperatures). Students sometimes confuse its impact on the compressor, which belongs to the compression side of the Brayton cycle.

Given Data / Assumptions:

• Multistage expansion with a reheater between turbine stages.
• Compressor configuration and pressure ratio unchanged.
• Steady-state operation without bleed air changes.

Concept / Approach:
Reheating raises the turbine-inlet temperature of downstream stages, thereby increasing turbine work output for a given pressure drop. The compressor is upstream of the combustor; its required work is determined by the pressure ratio, inlet condition, and compressor efficiency. Since reheating occurs after the compressor and within the turbine train, it does not alter the compression process.

Step-by-Step Solution:
Identify locations: Compressor → Combustor → Turbine 1 → Reheater → Turbine 2.Reheating changes the state entering Turbine 2, not the compressor inlet or pressure ratio.Therefore, compressor work remains the same for the same pressure ratio and efficiency.

Verification / Alternative check:
On a T–s diagram, reheating adds a horizontal rightward segment between turbine expansions; the compression path remains unchanged.

Why Other Options Are Wrong:

• Decrease/Increase: would require a pressure-ratio or inlet-state change on the compressor, which reheating does not cause.
• Reversal or zero work: physically impossible for a functioning compressor.

Common Pitfalls:
Assuming any turbine-side modification automatically affects the compressor load; only cycle pressure ratios, intercooling, or compressor-side heat exchange alter compressor work directly.

Final Answer:
Has no effect on compressor work