Effect of altitude on compressor power: For the same machine and similar operating conditions, an air compressor at high altitude generally requires less shaft power due to lower inlet density and reduced mass flow.

Introduction / Context:
Altitude changes ambient pressure and density, which affects the mass flow and power required by compressors and blowers. This question focuses on the qualitative trend for the same machine operated at higher elevation.

Given Data / Assumptions:

• Same compressor geometry and speed.
• Similar pressure ratio target relative to local ambient.
• Lower ambient pressure and density at altitude; temperature may also be lower but is a secondary factor here.

Concept / Approach:
Compressor power roughly scales with mass flow and with the specific work per unit mass. At higher altitude, the inlet density is lower, reducing mass flow for the same volumetric displacement. Even if the pressure ratio is maintained, the reduced m_dot lowers total shaft power.

Step-by-Step Solution:

Verification / Alternative check:
Aircraft and mountain-site installations derate compressor mass throughput and power with altitude; vendor correction curves confirm the trend.

Why Other Options Are Wrong:

• Same: Ignores strong density effect on mass flow.
• More: Opposite of the usual trend.
• Depends only on temperature: Pressure/density changes dominate.

Common Pitfalls:
Confusing pressure ratio referenced to sea level with pressure ratio relative to local ambient; always specify the operating basis.

Final Answer:
less