THERMODYNAMICS II
MIDTERM, FEB 17TH, 2011
MECH 351/4
CONCORDIA UNIVERSITY
FACULTY OF ENGINEERING AND COMPUTER SCIENCE
DEPARTMENT OF MECHANICAL ENGINEERING
Student's Name:
I.D.:
_______________________
_______________________
Notes:
State clearly any assumptions you make. If applicable, draw a sketch of the problem.
Return the questions paper with the answers book.
The maximum grade is 50.
Question no. 1 (30 Points)
A Rankine steam cycle modified for reheat, a closed feewater heater, and an
open feedwater heater is shown below. The high-pressure turbine receives 100
kg/s of steam from the boiler. The following data tables give the saturation data
for the pressures and data for h and s at selected states.
1. Sketch the T-s diagram for the ideal cycle.
2. Determine the net power output of the cycle, in MW.
3. If cooling water is available at 25ºC, what is the minimum flow rate of the
cooling water required in kg/s (i.e., for a maximum possible temperature
difference for the cooling water)? Take Cp (water)= 4.18 kJ/ kg . K.
1
THERMODYNAMICS II
MIDTERM, FEB 17TH, 2011
Process states and selected data
State
P (kPa)
T (ºC)
1
20
60.1
2
1400
3
1400
4
1400
5
5000
6
5000
700
7
1400
8
1200
9
1200
600
10
245
11
20
12
13
h (kJ/kg )
251.4
MECH 351/4
s (kJ/ kg . K)
532
830
3894
3400
3349
3692
3154
2620
532
7.504
7.504
7.504
7.938
7.938
7.938
NOTE: the work of all pumps is negligible compared to the work of the
turbines.
ANSWERS
Net power output
Minimum flow rate
of the cooling water
Question no. 2 (20 Points)
An ideal Diesel cycle has a maximum cycle temperature of 2000 oC and a cutoff ratio of
1.2. The state of the air at the beginning of the compression is P1 = 95 kPa and T1 = 15
o
C. This cycle is executed in a four-stroke; eight-cylinder engine with a cylinder bore of
10 cm and a piston stroke of 12 cm. The minimum volume enclosed in the cylinder is 5%
of the maximum cylinder volume. Determine the power produced by this engine when it
is operated at 1600 rpm. Use constant specific heats at room temperature: Cp = 1.005
k 1
kJ/kg.K and CV = 0.718 kJ/kg.K.
 T2 
v 
 1 
 
 T1  s cte  v2 
ANSWER
Power produced by
the engine
 T2 
P 
 2 
 
T
 1  s cte  P1 
 P2 
v 
 1 
 
P
 1  s cte  v2 
C
k p
Cv
k 1
k
k
2