Effect of reheating on gas-turbine performance In a simple gas turbine with reheating (expansion in multiple turbine stages with heat addition between them), which statement best describes the impact on overall cycle performance?

Introduction / Context:
Reheating inserts additional heat addition between turbine stages, allowing a higher average turbine inlet temperature during expansion. This boosts the specific turbine work but changes the average temperature at which heat is supplied, affecting overall efficiency.

Given Data / Assumptions:

• Simple Brayton cycle baseline with fixed compressor pressure ratio.
• Reheat applied between turbine stages, with comparable total-to-total efficiencies.
• No change to compressor side or pressure ratio due to reheat alone.

Concept / Approach:
Thermal efficiency = net work output / heat supplied. Reheating increases turbine work but requires additional fuel at a comparatively higher average temperature drop sequence that, in simple cycles, leads to a larger increase in heat input than in net work gain, thus lowering thermal efficiency. However, reheating can be beneficial where higher specific power is desired, or where constraints exist on turbine metal temperatures per stage.

Step-by-Step Solution:
Add reheat → turbine-stage inlet temperature raised for the second stage.Turbine work increases due to higher average expansion temperature.But additional heat input required outweighs the extra net work → efficiency falls.Therefore, among the options, ‘‘decreases the thermal efficiency’’ is correct.

Verification / Alternative check:
Cycle analysis and T–s diagrams show increased area for heat addition without proportional net-work increase; practical data confirm lower simple-cycle efficiency with reheat.

Why Other Options Are Wrong:
(a) Opposite of the usual simple-cycle effect; (b) compressor work is largely unaffected; (c) true locally but not the best single statement about overall cycle performance when only one choice is allowed.

Common Pitfalls:
Assuming more turbine work automatically means higher efficiency; efficiency depends on both net work and total heat input.

Final Answer:
Reheating decreases the thermal efficiency