Yeditepe University
Mechanical Engineering Department
ME 212 Thermodynamics II
Spring 2020 – HW 1
1) An insulated piston–cylinder device contains 3 L of
saturated liquid water at a constant pressure of 150 kPa.
An electric resistance heater inside the cylinder is turned
on, and electrical work is done on the water in the
amount of 2500 kJ. Assuming the surroundings to be at
25°C and 100 kPa, determine (a) the minimum work with
which this process could be accomplished and (b) the
exergy destroyed during this process.
2) Liquid water at 200 kPa and 20°C is heated in
600 kJ/min
a chamber by mixing it with superheated
steam at 200 kPa and 200°C. Liquid water
20°C
1
enters the mixing chamber at a rate of 3.5
MIXING
3.5 kg/s
kg/s, and the chamber is estimated to lose
60°C 3
CHAMBER
200
kPa
heat to the surrounding air at 25°C at a rate of
200°C
2
600 kJ/min. If the mixture leaves the mixing
chamber at 200 kPa and 60°C, determine (a)
the mass flow rate of the superheated steam and (b) the wasted work potential
during this mixing process.
3) Carbon dioxide, CO2, enters an adiabatic compressor at 100 kPa and 300 K,
and exits at 1000 kPa, 520 K. Write mass, energy and entropy balance
equations, calculate the specific compressor work, compressor isentropic
efficiency and the specific entropy generation for the process.
4) The heat exchanger uses the heat of hot exhaust gases to produce steam as
shown in figure, and a 15% of this heat is lost to the surroundings. Exhaust
gases enters the heat exchanger at 500°C. Water enters at 15°C as saturated
liquid and exit at saturated vapor at 2 MPa. The mass flow rate of water is
0.025 kg/s, and it is 0.42 kg/s for exhaust gases. The specific heat for exhaust
gases is 1.045 kJ/kg K, which can be treated as ideal gas. (a) Write mass and
energy balance equations; (b) Calculate the rate of heat transfer to the water;
(c) Calculate the exhaust gases exit temperature.