METU, ChE 204
Thermodynamics-1, Section 06
Prof. Dr. Tülay Özbelge
Asst. Emine Kayahan
April 8, 2014
HOMEWORK-6
(Due date: 15 April, 2014)
Problem 1. A well-insulated valve is used to throttle steam from 8 MPa and 500C to 6 MPa.
Determine the final temperature and the condition of the steam.
Problem 2. A 0.01-m3 cylinder containing nitrogen gas initially at a pressure of 200 bar and
250 K is connected to another cylinder 0.005 m3 in volume, which is initially evacuated. A
valve between the two cylinders is opened until the pressures in the cylinders equalize. Find
the final temperature and pressure in each cylinder if there is no heat flow into or out of
the cylinder. You may assume that there is no heat transfer between the gas and the cylinder
walls and that the gas is ideal with a constant-pressure heat capacity of 30 J/(mol K).
Problem 3. Repeat the calculation of Problem 2, but now assume that sufficient heat transfer
occurs between the gas in the two cylinders that both final temperatures and both final
pressures are the same.
Problem 4. An insulated tank is divided into two parts by a partition as shown in Fig. 1. One
part of the tank contains 2.5 kg of compressed liquid water at 60C and 600 kPa while the
other part is evacuated. The partition is now removed and the water expands to fill the entire
tank. Determine the final temperature of the water and the volume of the tank for a final
pressure of 10 kPa.
Evacuated
partition
H2O
Fig. 1
Problem 5. One mole of an ideal gas having Cp = (7/2) R and Cv = (5/2) R, is compressed
adiabatically in a piston/cylinder device from 1 bar and 40C to 4 bar. The process is
irreversible and requires 30 percent more work than a reversible, adiabatic compression from
the same initial state to the same pressure. What is the entropy change of the gas?
Problem 6. A steam turbine in a small electric power plant is designed to accept 4500 kg/h of
steam at 60 bar and 500C and exhaust the steam at 10 bar. Assuming that the turbine is
adiabatic and has been well designed (so that Sgen=0),
(a) compute the exit temperature of the steam and the power generated by the turbine.
(b) The efficiency of a turbine is defined to be the ratio of the work actually obtained from
the turbine to the work that would be obtained if the turbine operated isentropically
between the same inlet and exit pressures. If the turbine in part (a) is adiabatic but
only 80% efficient, what would be the exit temperature of the steam? At what rate
would entropy be generated within the turbine?
Problem 7. An inventor claims to have developed a power cycle which extracts 325 kJ of
heat from a reservoir at 325C, rejects 100 kJ of heat to a sink at 5C, and produces 225 kJ of
work.
(a) Is the device a violation of the first law?
(b) Is the device a violation of the second law, based on thermal efficiency data?
(c) Is the Clausius inequality satisfied?
Problem 8. The efficiency of heat engine operation on a Carnot cycle is 60 percent. A cooling
pond at 17C receives 106 J/min of heat from the engine. Determine (a) the power output of
the engine, in kilowatts, and (b) the temperature of the source reservoir.