The multistage compression as compared to single stage compression

Multistage Compression vs Single Stage Compression

Multistage compression is the term for a compression process that is completed in more than one stage, meaning that some of the air is compressed in one cylinder before being transported to another cylinder for more compression.

If we examine the volumetric efficiency expression, it demonstrates that the volumetric efficiency rises as the pressure ratio falls.

• In multistage compression: Pressure ratio in first stage = Pressure ratio in second stage
• For two-stage compression:
  • px = √p1p2
  • px/p1 = p2/px = (p2/p1)1/2
  • For N-stage compression:
  • px/p1 = (pd/ps)1/N
• The volumetric efficiency for multistage compression: ηv = 1 + C - C (Pd/Ps)1/Nn
  • where C is clearance ratio and n is polytropic index, N is number of stages and Pd and Ps are discharge and suction pressure.
• For multistage compression the pressure ratio (Pd/Ps)1/N is less than the single stage compression for same Pd/Ps.
• In other words, multistage compression boosts volumetric efficiency.
• With multiple stages of compression, the operational cost is reduced.
• Thus, multi-stage compression has lower running costs.

Summary:

The multistage compression as compared to single stage compression (a) improves volumetric efficiency for the given pressure ratio (b) reduces work done per kg of air (c) reduces cost of compressor (d) All of the above

Compressor costs are lower with multistage compression than with single-stage compression. The multistage compressor has more than two piston cylinders of different diameters.