Exam 7: Entropy

The temperature of a cold orange with an average mass of 0.28 kg and average specific heat of 3.42 kJ/kg.SYMBOL 176 \f "Symbol"C rises from 7°C to 25°C as a result of heat transfer from the suroundign air. The entropy change of the orange is

Steam is compressed from 4 MPa and 300SYMBOL 176 \f "Symbol"C to 9 MPa isentropically. The final temperature of the steam is

Air at 900 kPa and 25°C is allowed to expand steadily and isothermally to 100 kPa at a rate of 1.4 kg/s. The maximum power output of the turbine is

Water enters a pump steadily at 180 kPa at a rate of 0.012 m³/s and leaves at 1200 kPa. If the pump efficiency is 0.75 and the changes in kinetic and potential energies are negligible, the power input to the pump is

Argon gas is compressed steadily from 100 kPa and 25°C to 700 kPa at a rate of 0.15 kg/min by an adiabatic compressor. If the compressor consumes 35 kW of power while operating, the isentropic efficiency of this compressor is

Water enters a pump steadily at 180 kPa at a rate of 0.012 m³/s and leaves at 1200 kPa. If the changes in kinetic and potential energies are negligible, the minimum power input to the pump is

R134a is condensed at a constant temperature of 30°C as it flows through the condenser of a refrigerator by rejecting heat at a rate of 6 kW. The rate of entropy change of R134a as it flows through the condenser is

Steam expands in an adiabatic turbine from 8 MPa and 450°C to a pressure of 50 kPa at a rate of 1.8 kg/s. The maximum power output of the turbine is

Argon gas is compressed from 150 kPa nd 25°C to a pressure of 700 kPa adiabatically. The lowest temperature of argon after compression is

Helium gas expands in an adiabatic turbine from 2 MPa and 750°C to 0.18 MPa at a rate of 1.5 kg/s. Assuming constant specific heats at room temperature, the maximum power output of the turbine is

Air is compressed from 30°C and 4.2 L to a volume of 0.50 m³ in a reversible adiabatic manner. The air temperature after compression is

Helium gas expands in an adiabatic turbine steadily from 700°C and 900 kPa to 70 kPa at a rate of 0.15 kg/s. For an isentropic efficiency of 82%, the power produced by the turbine is

Air is compressed steadily and adiabatically from 15°C and 90 kPa to 310°C and 600 kPa. Assuming constant specific heats for air at room temperature, the isentropic efficiency of the compressor is

Liquid kerosene with a specific heat of 2.0 kJ/kg.°C enters an adiabatic piping system at 18° at a rate of 3 kg/s. If the water temperature rises by 0.4°C during flow due to friction, the rate of entropy generation in the pipe is

Heat is lost through a plane wall steadily at a rate of 750 W. If the inner and outer surface temperatures of the wall are 50°C and 15°C, respectively, the rate of entropy generation within the wall is

Air is to be compressed steadily and isentropically from 2 atm to 18 atm by a two-stage compressor. To minimize the total compression work, the intermediate pressure between the two stages must be

Refrigerant-134a enters an adiabatic compressor as saturated vapor at 0.18 MPa at a rate of 1.6 kg/s, and exits at 1 MPa and 60°C. The rate of entropy generation in the turbine is

Combustion gases with a specific heat ratio of 1.34 enter an adiabatic nozzle steadily at 720°C and 400 kPa with a low velocity, and exit at a pressure of 100 kPa. The lowest possible temperature of combustion gases at the nozzle exit is

A unit mass of an ideal gas at temperature T undergoes a reversible isothermal process from volume V₁ to volume V₂ while loosing heat to the surroundings at temperature T in the amount of q. If the gas constant of the gas is R, the entropy change of the gas $\Delta$ s during this process is

Refrigerant-134a enters an adiabatic turbine steadily at 40°C and 0.9 MPa, and leaves at 140 kPa. The highest possible percentage of mass of R134a that condenses at the turbine exit and leaves the turbine as a liquid is