Fall 2010
ME 301
Period:
5th
6th
A. R. Mech
Exam #1
Open Text Book
One 8.5” x 11” Equation Sheet (both sides)
[No Worked Examples, ALEs or HW allowed]
Laptops Permitted for Calculations & Music Only
[EES is NOT permitted; music must not disturb others.]
NAME_________________
BOX
.
SCORE
Problem 1
______ / 60
Problem 2
______ / 30
Problem 3
/ 10
Total
______ /100
PLEASE NOTE:
The problems 1 & 2 are printed on the inside of this folder. Please write their
solutions on blank paper provided. Please write the solution to problem 3 on the
question sheet.
Please put your name and CM box on each sheet.
Submit your equation sheet and solutions in the folder before you leave.
DO NOT INTERPOLATE! Use the closest value in the tables.
Problem 1 (60 pts)
Consider the reheat STEAM cycle at the right.
Partial data are provided in the table below. Kinetic
and potential energies are negligible.
6
STM GEN
HPT
1
2
(a) [22 pts] Determine the thermal efficiency of
the cycle.
3
(b) [10 pts] Determine the adiabatic (isentropic)
efficiency of the pump.
LPT
4
7
(2nd
(c) [18 pts] Determine the exergetic
Law)
efficiency of the low pressure turbine (LPT).
(d) [10 pts] Determine the exergy destruction of
the LPT per unit mass of steam in kJ/kg.
CNDSR
PUMP
5
HINT: Only find the property data necessary to complete the computations. Much of the table
can be left blank.
RECALL: Use the closest table value. Don’t interpolate.
State
T [°C]
P [bars]
h [kJ/kg]
0
17
1.013
71.48
1
2s = 2rev
2
560
180
s
[kJ/(kg K)]
0.2535
af [kJ/kg]
other
0
environment (dead state)
3275.0
3
4s = 4rev
4
3575.0
0.7
0.7
2675.0
5
6s
6
0.7
180
180
400.00
7.1000
Problem 2 (30 pts) (put answers on this page and show work on separate sheet)
A mass of 0.3 kg of air is compressed in an
insulated piston-cylinder from 17°C and
1 bar to 127 °C and 3 bar. The surroundings
are at T0 = 23°C, P0 = 1 bar.
Find the increase in the exergy of the air
in the cylinder.
AIR
m=0.3 kg
P1=1 bar; P2=3 bar
T1=17°C; T2=127°C
P0=1 bar
T0=23°C
8
Problem 3 (10 pts) (put solution on this page)
Answer this question using the T-s diagram below (drawn to scale); you do not need to perform
calculations to get full credit.
An ideal Rankine cycle with reheat has a boiler pressure of 1500 kPa, a reheat pressure of 500 kPa,
and a condenser pressure of 10 kPa. The boiler and reheat exit temperatures are both 500 °C.
(a) [4 pts]
Draw (as close to scale as you can) the cycle on the T-s diagram below.
Steam
500
400
T [°C]
300
3000 kPa
200
1500 kPa
500 kPa
100
10 kPa
0
0.0
2.0
8.0
6.0
4.0
10.0
s [kJ/kg-K]
(c) [6 pts]
(Circle the correct answer.) If the boiler pressure was increased to 3000 kPa, will:
the quality of the steam
entering the condenser
increase
decrease
stay same
the net work out per kg
increase
decrease
stay same
the thermal efficiency
increase
decrease
stay same