Jet engines employ ________ type of compressor.

Question

Question

This question was previously asked in

NHPC JE Mechanical 6 April 2022 (Shift 1) Official Paper

Answer 1

Explanation:

In an axial flow compressor, the flow proceeds throughout the compressor in a direction essentially parallel to the axis of the machine.
Axial flow compressors are used in all larger gas turbine units because of their high efficiency and capacity (larger air handling ability).
Centrifugal compressors are more stable than axial flow ones but of much low capacity and not as efficient.
The delivery pressure in the Axial flow compressor is about 20 bar and in the centrifugal compressor is about 40 bar and the pressure rise in per stage for an axial compressor is 1.25 and for a centrifugal compressor is 5, Therefore, an axial flow compressor is suitable for the low-pressure rise.

Aspect of comparison	Axial flow compressor	Centrifugal compressor
Type of flow	Parallel to the axis	Radial
Pressure Ratio/Stage	About 1.25	5
Isentropic efficiency	Higher (86 to 90%)	Lower (80 to 82%)
Frontal area	Smaller	Larger
Mass flow rate	Large (>100 kg/s)	Small (<15 kg/s)
Flexibility of operation	Limited	Higher
Part load performance	Poor	Better
Starting Torque	High	Low
Suitability for multistage	More suitable	Difficult
Delivery pressure	Lower (20 bar)	Higher (about 40 bar)
Applications	Jet engines, stationary industrial gas turbine power plants and steel mills	Steel mills, low-pressure refrigeration, Big central air-conditioning plants, fertilizer industry, IC engines
Fixing and manufacturing	Not easy	Easy
Cost	Very expensive	Cheap