Gas turbines with intercooling: effect on compressor work input In a gas-turbine plant that uses multistage compression with intercooling between stages, how does the required compressor work with intercooling compare to the work with no intercooling (same overall pressure ratio)?

Introduction / Context:
Intercooling in gas turbines is a classic method to reduce compressor work. By removing heat between compression stages, the specific volume of the air entering the next stage is lowered, which reduces the work of subsequent compression for a given overall pressure ratio. This question tests conceptual understanding of why intercooling decreases the compressor power requirement.

Given Data / Assumptions:

• Same overall pressure ratio across the compressor with and without intercooling.
• Idealized discussion: negligible pressure losses in intercoolers and ducting.
• Working fluid treated as a perfect gas with approximately constant specific heats over the compression range.

Concept / Approach:
Compressor work depends on the average specific volume during compression. Cooling the air between stages brings the temperature closer to the initial value, which reduces specific volume and hence the area under the p–v diagram for compression. On a T–s diagram, for the same pressure rise, intercooling moves the path closer to isothermal, lowering the enthalpy rise per kilogram and therefore the work input.

Step-by-Step Solution:

Verification / Alternative check:
For ideal equal pressure-ratio staging with perfect intercooling (temperature restored to the original value), the minimum total compressor work is achieved. Analytical expressions for polytropic compression confirm a reduced enthalpy rise when intermediate cooling is applied.

Why Other Options Are Wrong:

Equal to: contradicts thermodynamics; intercooling reduces work.More than: removing heat cannot increase ideal compression work.Cannot be predicted / depends only on combustor efficiency: compressor work is determined by compression thermodynamics, not combustor performance.

Common Pitfalls:
Assuming intercooling always improves overall cycle efficiency; while it cuts compressor work, it also increases heat added in the combustor because the compressed air is cooler, which can reduce thermal efficiency unless regeneration is used.

Final Answer:

less than the work with no intercooling