Mechanical Engineering - Compressors, Gas Dynamics and Gas Turbines - Discussion

At higher altitudes molecules of air are few, hence a compressor supplies smaller volume of air at a higher altitude so it requires less power.

Answer "B" is correct. Less power will be required by the compressor to compress the air as the density of the air/air pressure reduces at higher altitudes.

At high altitude, the less power will require because compression ratio will be less.

So Answer B is correct.

At elevated altitudes, lower atmospheric pressure means that the air molecules are less tightly packed together and therefore have a lower density. When an air compressor draws in air as part of its intake process it's typically a fixed volume of air so if the air density is less it means that there is fewer air molecules drawn into the compressor's cylinders/rotor lobes/vanes. Less air drawn in means less air compressed and less air delivered to the receiver tank and tools per compression cycle.

So as per question, JUST TO RUN COMPRESSOR, LESSER POWER IS REQUIRED, WHICH IS CORRECT.

Pressure decreed as height increases Due to low suction pressure compressor will require more power.

More power required for same compression ratio. And the performance of engine decreases at high altitude.

The Answer is B.

Another factor to consider is the effect of altitude and air density on the operation of the engine that is powering the compressor. As altitude increases the air density decreases resulting in a roughly proportional decrease in the horsepower your engine is able to produce. A normally aspirated diesel engine might have 10% less power available at 800m/2600ft and 20% at 1600m/5200ft compared to operation at sea level. Different engines will have different de-rate curves depending on the engine design, for example, some turbocharged engines can compensate for the effects of altitude. Reduced engine power can result in a situation where the engine bogs down and the RPM drops which results in fewer compression cycles per minute and therefore less compressed air output. In extreme cases, the engine may not be able to run the compressor at all without stalling.

For same compression ratio, discharge pressure is low because of low suction pressure at higher latitudes so power required is less. At higher pressure, further compression required more power.

More power is required for same compression ratio.

Yes, higher power required.