The Copperbelt University
School of Engineering
Knowledge and Service
Thermodynamics
Tutorial
Course Code: EM 341
Instructions: Answer All
School of Engineering
QUESTION 1
Air is contained in a rigid well-insulated tank with a volume of 0.6 m3. The tank is fitted with a
paddle wheel that transfers energy to the air at a constant rate of 4 W for 1 h. The initial density
of the air is 1.2 kg/m3. If no changes in kinetic or potential energy occur, determine:
a) The specific volume at the final state, in m3/kg
b) The energy transfer by work, in kJ.
c) The change in specific internal energy of the air, in kJ/kg.
[Answer 0.833 m3/kg, -14.4 KJ and 20 KJ/kg]
QUESTION 2
Air enters a one-inlet, one-exit control volume at 6 bar, 500 K, and 30 m/s through a flow area of
28 cm2. At the exit, the pressure is 3 bar, the temperature is 456.5 K, and the velocity is 300 m/s.
The air behaves as an ideal gas. For steady-state operation, determine
(a) The mass flow rate, in kg/s.
(b) The exit flow area, in cm2
[Answer 0.35 kg/s and 5.1 cm2 ]
QUESTION 3
A thermodynamic steady flow system receives 4.56 kg/min of fluid where P1 = 137.90 KPa, v1 =
0.0388 m3/kg, ν1 = 122 m/s, and u1 = 17.16 KJ/kg. The fluid leaves the system at boundary
where P2 = 551.6 KPa, v2 = 0.193 m3/kg, ν2 = 183 m/s and u2 = 52.80 KJ/kg. During the passage
through the system the fluid receives 3,000 J/s of heat. Determine the work in KJ/min.
[Answers -486kJ/min]
QUESTION 4
Air flows steadily at the rate of 0.5 kg/s through an air compressor, entering at 7 m/s velocity,
100kPa pressure, and 0.95 m3/kg volume, and leaving at 5 m/s, 700 kPa, and 0.19 m3/kg. The
internal energy of the air leaving is 90 kJ/kg greater than that of the air entering. Cooling water
in the compressor jackets absorbs heat from the air at the rate of 58 kW.
a) Compute the rate of shaft work input to the air in kW.
b) Find the ratio of the inlet pipe diameter to outlet pipe diameter
[Answer -122 kW and 1.89]