An insulated air compressor receives 0.65 lbm/s of air at 14.7 psia and 70oF. The air is compressed to 125 psia. For exit temperatures ranging from 550oF to 750oF, use your compressor model to plot the power required by the compressor. (The higher the exit temperature, the less efficient the compressor is.)

Question

Given: P1 = 14.7 psia; T1 = 70oF; m?= 0.65 lbm/s; P2 = 125 psia;
Air (Take State 1 as the inlet, State 2 as the outlet.)
Assume: Q?=0 (insulated). For a compressor, assume steady-state, steady-flow, single-inlet, single-outlet flow, with ?KE = ?PE = 0
What will be an ideal response?

Answer 1

With these assumptions, the First Law for open systems reduces to W?=m?(h1?h2)

As the temperature change can get large, we will consider the specific heats of the air to be variable.

h1 = 126.66 Btu/lbm

The exit enthalpy is a function of exit temperature.



You may note that the curve is slightly non-linear with the variable specific heats of the air incorporated. Also, the power consumption increases as the efficiency decreases (as represented by increasing exit air temperatures).