Class 4 (4th Engineer) MEKG 📅 Jul 2023

Exam Question

(a) Explain the basic theory of air compressors using a basic P-V cycle diagram, for a single stage air compressor, showing (6)

(i) Adiabatic

(ii) Polytropic

(iii) Isothermal lines of compression

(b) Explain the advantages of multistage compression and intercooling. Superimpose the effects of both on the P-V diagram mentioned above. (6)

Reference Answer

### (a) Basic Theory of Air Compressors and P-V Diagram
The theoretical operation of a single-stage reciprocating air compressor can be analyzed using a Pressure-Volume (P-V) diagram. The diagram illustrates the relationship between the pressure and volume of the air inside the cylinder during one complete cycle. The area enclosed by the cycle on the P-V diagram represents the net work done on the air per cycle.
The cycle, assuming no clearance volume for simplicity, consists of three main processes:
* **D-A: Suction Stroke:** The piston moves from Top Dead Center (TDC) to Bottom Dead Center (BDC). The inlet valve opens, and a volume of air (V_A) is drawn into the cylinder at a constant suction pressure, P1 (typically atmospheric).

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