An insulated air compressor receives 0.25 kg/s of air at 100 kPa and 20°C. The air is compressed to 900 kPa. For exit temperatures ranging from 290°C to 400°C, use your compressor model to plot the power required by the compressor. (The higher the exit temperature, the less efficient the compressor is.)
Given: P1 = 100 kPa; T1 = 20°C; m?= 0.25 kg/s; P2 = 900 kPa;
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?
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 = 293.17 kJ/kg
The exit enthalpy is a function of exit pressure.
The resulting power requirement plot is
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).
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