Unformatted text preview: Air is compressed steadily by a compressor from
100 kPa and 17°C to 700 kPa at a rate of 5 kg/min. Determine
the minimum power input required if the process is (a) adiabatic and (b) isothermal. Assume air to be an ideal gas with
variable specific heats, and neglect the changes in kinetic and
potential energies. Answers: (a) 18.0 kW, (b) 13.5 kW.
7–143 Air enters a two-stage compressor at 100 kPa and
27°C and is compressed to 900 kPa. The pressure ratio across
each stage is the same, and the air is cooled to the initial temperature between the two stages. Assuming the compression 90%
10% 50 kPa FIGURE P7–145
7–146 Steam enters a two-stage adiabatic turbine at 8 MPa
and 500°C. It expands in the first stage to a pressure of 2 MPa.
Then steam is reheated at constant pressure to 500°C before it
is expanded in a second stage to a pressure of 100 kPa. The
power output of the turbine is 80 MW. Assuming an isentropic
efficiency of 84 percent for each stage of the turbine, determine cen54261...
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