THE THEORY OF COMPRESSION
Question 1.
(a) What effect does isothermal compression have on the enthalpy of air? Explain your answer.
(b) Which thermodynamic process for compressing air requires the greatest energy input? Explain your answer with the aid of a p-V diagram.
(c) How is the volumetric efficiency of a compressor defined?
(d) Explain why it is not practically possible to achieve isothermal compression of air.
Question 2. Air is compressed from a temperature of 25°C and pressure of 1 bar and the index of compression is 1.25. If the delivery temperature of the air is 300°C and the power input to the compressor is 5 kW, calculate:
(a) The pressure of the air after compression.
(b) The volume of free air (at 1 bar and 25°C) compressed per minute.
(c) The volume of the receiver required to hold the air after the compressor has been running for 1 hour.
(d) The power required if air is compressed to the same pressure at the same rate isothermally.
(e) The isothermal efficiency of the polytropic compression.
Question 3. (a) Calculate the volume of free air (at 1 bar and 25°C) which can be compressed per minute to a pressure of 9 bar using two stage polytropic (n = 1.3) compression with a total input power of 3 kW.
(b) What will be the delivery temperature after the second stage of compression, assuming the air is cooled to 25°C after intercooling?