Name_____________________________
Summer 2009
Test 3
1. (12 pts) Air enters an adiabatic turbine at 1400 K and 2.0 MPa and exits the
turbine at 100 kPa. The isentopic efficiency of the turbine is 65% and it
produces 110 MW of power. Using VARIABLE specific heat analysis, determine
the mass flow rate of air.
2. (12 pts) A freely moving piston cylinder device has an initial temperature of 600
K, pressure of 300 kPa and volume of 1 m3. The system loses heat to the
atmosphere until it reaches thermal equilibrium with the surroundings, which
are at 18oC. Determine the entropy generated from this process (Sgen).
3. (16 pts) A 3.5 ton, simple vapor compression refrigeration system operates with
R134a as the working fluid. The refrigerant leaves the evaporator at 200 kPa
and 95% quality and it leaves the condenser at 2.0 MPa and 50oC. Determine the
power consumed by the compressor and the COP of the system.
Name_____________________________
Summer 2009
Test 1
Open Book/Notes Portion (33 pts)
1. (14 pts) An ideal gas contained within a 1,000 gallon rigid tank has an initial
pressure of 5 MPa and initial temperature of 25oC. A circulation mechanism
(fan) placed inside the tank consumes 150 W of power and it operates for 8
hours. The final temperature of the fluid in the tank is 88oC, the gas constant, R,
is 1.386 kJ/kg.K, the constant volume specific heat capacity, cv, is 1.2 kJ/kg.K and
the constant pressure specific heat capacity, cp, is 1.9 kJ/kg.K. Determine:
a. (3 pts) The mass of air contained in the tank
b. (3 pts) The final pressure inside the tank
c. (8 pts) The amount and direction of heat transfer
2. (19 pts) 25 kg of water is contained in a piston-cylinder device at 500 kPa.
Initially, 12 kg are in liquid phase and the rest is vapor. Heat is transferred to
the system until the volume doubles, at which time the piston hits a set of stops
restraining its expansion. Heat transfer continues until the pressure reaches 1
MPa. Determine:
a.
b.
c.
d.
e.
(2 pts) The initial temperature
(3 pts) The final temperature
(6 pts) The boundary work
(6 pts) The heat transfer
(2 pts) Draw the process on a P-v diagram