A heavily insulated piston–cylinder device contains 0.039 m3 of steam at 300 kPa and 150°C. Steam is now compressed in a reversible manner to a pressure of 1 MPa. Determine the work done on the steam during this process.

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A piston-cylinder device contains 2 lbm of refrigerant R-134a at 120 psia and 100 °F. The refrigerant is now cooled at constant pressure until it exists as a liquid at 50 °F. Determine the entropy change during the process.

Solution

Liquid water at 120 kPa enters a 7-kW pump where pressure is raised to 5 MPa, elevation difference from inlet to exit levels is 10 m, determine highest mass flow rate this pump can handle. Neglect kinetic energy change and take specific volume of water to be 0.001m^3/kg

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Helium gas is compressed from 16 psia and 85°F to 120 psia at a rate of 10 ft3/s. Determine the power input to the compressor, assuming the compression process to be 
(a) isentropic
(b) polytropic with n = 1.2
(c) isothermal
(d) ideal two-stage polytropic with n = 1.2.

Solution

Liquid water enters a 25-kW pump at 100-kPa pressure at a rate of 5 kg/s. Determine the highest pressure the liquid water can have at the exit of the pump. Neglect the kinetic and potential energy changes of water, 
and take the specific volume of water to be 0.001 m3/kg. 

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A constant-volume tank contains 4.840 kg of air at 100 kpa and 327 degreesC. The air is cooled to the surroundings temperature of 27 degreesC. Assume constant specific heats at 300 K. 

Determine the entropy change of the air in the tank during the process and the net entropy change of the universe do to this process.

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An ideal gas at 101 kPa and 27 degrees C enters a steady-flow compressor. The gas is compressed to 404 kPa, and 10% of the mass that entered the compressor is removed for some other use. The remaining 90% of the inlet gas is compressed to 580 kPa before leaving the compressor. The entire compression process is assumed to be reversible and adiabatic. The power supplied to the compressor is measured to be 32.2 kW. If the ideal gas has constant specific heats such that c(v)=0.71 kJ/kg*K and c(p)=1.26 kJ/kg*K,

determine the temperature of the gas at the two compressor exits
determine the mass flow rate of the gas into the compressor

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