College of Engineering
Spring Session- 2016 THERMODYNAMICS II - ME 272
Dr. Saeed J. Almalowi, [email protected]
ME 272-College of Engineering-Taibah University
PROBLEM 2.1 STATEMENT
A piston-cylinder device contains 0.05 kg of steam at 1 MPa and 300oC. Steam now expands to a
final state of 200 kPa and 150oC, doing work. Heat losses from the system to the surrounding are
estimated to be 2 kJ during this process. Assuming the surrounding to be To = 25oC and Po =100
kPa,
Determine
a. The exergy of the steam at the initial and the final state,
b. The exergy change of the steam,
c. The useful work,
d. The exergy destroyed, and
e. The second law efficiency?
Fig.2.1 A Piston-Cylinder
Ans. [X1=35 kJ, X2=25.4 kJ, Wu=5.3 kJ, Xdestroyed=4.3 kJ, and ฮทII =55.2 %]
Solution:
X1= m(u1โuo)+mPo(ฮฝ1โฮฝo)โmTo(s1โso)+1
2mV1
2+mgz1
X2= m(u2โuo)+ mPo(ฮฝout โฮฝo)โmTo(s2โso)+1
2mV2
2+mgz2
State
Description of state
Internal energy
kJ/kg
Entropy
kJ/kg.K
Specific Volume
m3/kg
State (1) P1= 1000 kPa
T1=300oC
T1>Tsat. @ P1=1000 kPa
Superheated steam
u1=2794
s1=7.122
v1=0.2579
State(2) P2 =200 kPa,
T2=150oC
T2>Tsat. @ P2=200 kPa
Superheated steam
u2=2577
s2=7.279
v2=0.9597
Surrounding State:
Dead state* To=25oC,
P0=100 kPa
Compressed Liquid
uo=104.7
so= 0.3669
vo=0.001003
