ENGR 30 F2009
Exam 2
11/09/2009
Closed Notes. Open Book.
Do all the three problems.
1.
Steam at 5 MPa and 350
0
C is being used to generate power in an adiabatic turbine
whose exit pressure is 80 kPa and it comes out as saturated steam. How much power
can we expect to generate using this turbine if steam flow rate through the turbine is
15 kg/s?
What will happen to power generated per kg of steam passing through it if the turbine
is not adiabatic and loses heat at a rate of 25 kJ/kg steam?
Solution: Assume steady state operation, negligible changes in KE and PE.
Governing equation: m h
in
– m h
out
+ Q
in
– W
out
= 0
(a) Adiabatic operation > Q
in
= 0 kJ/s
m = 15 kg/s
Inlet: Steam at 5 MPa and 350
0
C
This is superheated steam since 350
0
C > T
sat
at 5 MPa
From superheated steam tables
h
in
= 3069.3 kJ/kg
Outlet: Saturated steam at 80 kPa
From pressure table for saturated water
h
g
= 2662.4 kJ/kg at 75 kPa
h
g
= 2675.0 kJ/kg at 100 kPa
> h
out
= 2662.4 + (2675.0 – 2662.4) (8075)/(10075) = 2664.92 kJ/kg
Using governing equation: W
out
= (15 kg/s) (3069.3 – 2664.92) kJ/kg
= (15 kg/s) (404.38 kJ/kg) = 6075.7 kJ/s or kW
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '09
 Staff
 Thermodynamics, kPa, Qin

Click to edit the document details