ME 336 EXAM 2,
NOVEMBER 25, 2008
C. BORGNAKKE, ME Dept.
Problem 1 [40 Points]
A Brayton cycle has the inlet at 290 K, 100 kPa and uses a compression ratio of 12:1. It
has the highest temperature of 1600 K and employs an ideal regenerator. Use cold air
properties to solve.
a) Find the specific net work
b) Find the cycle efficiency
c) Find the cycle 2
nd
law efficiency.
Problem 2 [40 Points]
A refrigerator uses R134a with the state into the condenser as 800 kPa, 40
°
C and the exit
of the condenser is saturated liquid at 25
°
C. The mass flow rate is 0.1 kg/s and the low
pressure in the cycle is 165 kPa. The condenser has air flowing in at ambient temperature
20
°
C and leaving at 35
°
C.
Find the minimum flow rate of air needed.
Find the cycle COP
Find the condenser second law efficiency.
Problem 3 [20 Points]
A closed feedwater heater with a trap heats 20 kg/s water from 100
°
C to 250
°
C
at 20
MPa. The extraction steam from the turbine enters at 4 MPa, 275
°
C and leaves as
saturated liquid. What is the required mass flow rate of the extraction steam?
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 Fall '09
 Borgnakke
 Energy, HMS H2, Mass flow rate, HMS H1, British H class submarine

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