EML
3015C Thermal-fluids I Sample Test #3 fall
1999
1.
(45%)Considering
the ideal Rankine power plant as shown.
The steam mass flow rate is 60 kg/s.
The steam is first heated in the boiler at a constant pressure of 8 MPa
and expands in the first turbine to become 100% saturated vapor before it is
reheated again at a constant pressure of 0.8 MPa before entering the second
turbine. Finally, the heat is rejected
to a condenser unit operating at a pressure of 10 kPa. In order to remove the heat in the condenser
unit, cooling water enters at 20°C and leaves at 60°C at a mass flow rate of 750 kg/s. Determine (a) The power input of the pump,
(b) The heat rejection of the condenser unit, (c) The work output of the first
stage turbine, (d) the work output of the second stage turbine, (e) the total
heat transfer into the power plant, (f) thermal efficiency of the power plant.
|
P(MPa) |
T(°C) |
x
(%) |
h
(kJ/kg) |
s
(kJ/kgK) |
v
(m3/kg) |
1 |
0.01 |
45.8
(C-2) |
0 |
191.8 |
|
0.00101 |
2 |
8 |
|
|
199.9 |
|
|
3 |
8 |
|
|
3352.5 |
6.6636 |
|
4 |
0.8 |
170.4(C-2) |
100 |
2769.1 |
6.6636 |
|
5 |
0.8 |
|
|
3056.4 |
7.236 |
|
6 |
0.01 |
45.8
(C-2) |
87.8 |
2291.8 |
7.236 |
|
A-6 A-6 A-5
2.
(25%)Steam
enters the turbine steadily at 8 MPa and 400°C and leaves at a pressure
of 1 MPa. Determine (a) the work output
if the process is isentropic. If the
actual turbine is operating at 70% isentropic efficiency, determine (b) the
actual work output, (c) the actual exit temperature of the steam, (d) the
entropy generation (assume adiabatic). Base your calculation on 1 kg/s of
steady steam flow.
3.
(30%) A cylinder and piston assembly, containing 1 kg of air, is undergoing a
complete cycle consisting of three reversible processes: 1-2 is an isentropc
compression; 2-3 is an isothermal expansion from a pressure of 1 MPa to 100
kPa; and 3-1 is a constant pressure compression to a temperature of 50°C.
Sketch the T-s and P-v diagrams representing this cycle. Determine the total work and heat transfer
of the cycle. Assume ideal gas (Cp=1
kJ/kg K, Cv=0.72 kJ/kg K, R=0.287 kJ/kg K, k=Cp/Cv=1.4)
|
P
(MPa) |
T
(K) |
v
(m3/kg) |
1 |
0.1 |
323 |
0.927 |
2 |
1 |
623.6 |
0.179 |
3 |
0.1 |
623.6 |
1.790 |
Formula Sheet