Department of Mechanical Engineering
ME 322 – Mechanical Engineering
Thermodynamics
Lecture 15
Nozzles/Diffusers, Valves, Heat XGERs
The Laws of the Universe
Conservation of Mass – The Continuity Equation
m  m
i
i

e
e
dmsys
dt
Conservation of Energy – The First Law of Thermodynamics
Q W 

i
2

Vi 2
g 
m i  hi 
 zi  
2 gc gc 


e

Ve2
g  dEG
m e  he 
 ze  
2 gc gc  dt

Steam Whistle
6.13 A steam whistle is devised by attaching a simple converging nozzle to a steam line. At the inlet
to the whistle, the pressure is 60 psia, the temperature is 600°F, and the velocity is 10 ft/s. The steam
expands and accelerates horizontally to the outlet, where the pressure and temperature are 14.7 psia and
500°F. Determine the stem velocity at the whistle outlet. Assume the process is adiabatic, aergonic,
and steady flow.
1
2
P1  60 psia
T1  600F
V1  10 ft/s
P2  14.7 psia
T2  500F
SS, adiabatic, aergonic nozzle


V12
V22
g 
g  dEG
Q  W  m1  h1 
 z1   m2  h2 
 z2  
2 gc gc 
2 gc gc  dt


dmsys
i mi  e me  dt
3
Throttling Valve
6.19 Wet steam is throttled adiabatically and aergonically from 800 psia to 5 psia and 200°F.
If the inlet and exit velocities and heights are equal, what is the ratio of the exit area to the inlet
area for this device?
1
2
P2  5 psia
T2  200F
P1  800 psia
V1  V2
SS, adiabatic, aergonic throttling


V12
V22
g 
g  dE
Q  W  m1  h1 
 z1   m2  h2 
 z2   G
2 gc gc 
2 gc gc  dt


m  m
i
i
4
e
e

dmsys
dt
Feedwater Heater
6.30 The steady state, steady flow, adiabatic, aergonic feedwater heater shown is used in an electric
power plant. It mixes superheated steam with saturated liquid water to produce a low-quality
outflow, in which 10 lbm/s of superheated steam at 80 psia and 500°F is mixed with saturated liquid
water at 80 psia. The outlet stream has a quality of 10% at 80 psia. What is the mass flow rate of
the saturated liquid water flow stream?
P1  80 psia
T1  500F
m1  10 lbm/s
P2  80 psia
x2  0
1
Feedwater Heater
3
2
P3  80 psia
x3  0.10
SS, adiabatic, aergonic direct contact HX



V32
V12
V22
g 
g 
g  dE
Q  W  m1  h1 
 z1   m2  h2 
 z2   m3  h3 
 z3   G
2 gc gc 
2 gc gc 
2 gc gc  dt



dmsys
i mi  e me  dt
5