Transcript EGR 4347 Analysis and Design of Propulsion Systems

EGR 4347 Analysis and Design of Propulsion
Systems
Review
EGR 4347 - Review
Explain the difference between units and
dimensions.
Dimensions – physical quantity that can be
characterized EX. length, mass
Units – arbitrary magnitudes assigned to the
dimensions EX. meter, feet
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Explain extensive and intensive properties.
Extensive depends on system
Intensive is independent of system
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Give at least four forms of energy which make
up the term total energy, E.
1. Thermal
2. Mechanical
3. Potential
4. Electric
5. Chemical
6. Nuclear
7. Kinetic
8. Magnetic
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Give the unit of mass in the SI, Old English
and English Engineering system.
SI - kg
Old English - lbm
English Engineering - slug
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What is gc and how is it used?
Conversion constant - used with mass
What is a simple compressible substance?
The only important reversible work mode is
volume change or pdv work.
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What is the state postulate?
The state of a simple compressible system is
completely specified by two independent,
intensive properties.
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What is a perfect or ideal gas (physical meaning)?
No dissociation
Intermolecular forces negligible
Occurs at low pressures and high temperatures
(compared to critical point)
What is the ideal gas law?
P=RT
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Explain R in the ideal gas law.
Specific Gas Constant-depends on
molecular weight
Give the equation for and define the
Conservation of Mass.
dm/dt = 0
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Give the equation for and define Continuity.
.
.
m in  m out
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Give the equation for and define 1st Law for a
Control Volume.
.
.
.
Q in  W in  min (h  pe  ke)in 
.
.
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Q out  W out  m out (h  pe  ke) out
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Give the equation for and define the 2nd law
for a Control Volume.
.
SCV
Qk
  mi si   me se  S gen  
0
Tk
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Define adiabatic.
No heat interaction.
Define reversible.
A process that can be reversed without
leaving any trace on the surroundings.
Define isentropic.
ds=0
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Is an adiabatic, reversible process isentropic?
Yes
Is an isentropic process always adiabatic and
reversible?
No
Is an isentropic, adiabatic process reversible?
Yes
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Is an isentropic, reversible process always
adiabatic?
No
What is a calorically perfect gas?
cp/cv = constant = 
For a calorically perfect gas what is du?
du=cvdT
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For a calorically perfect gas what is dh?
dh=cpdT
What is Gibbs Equation?
Tds=dh-vdp=du+pdv
What is specific enthalpy?
h=u+pdv
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Define total properties.
Fluid brought to rest isentropically (or
adiabatically)
Write the equation for total enthalpy and total
temperature.
ht=h+V2/(2gc) Tt=T+V2/(2gccp)
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Explain the concept of isentropic efficiency as
it applies to a turbine.
wa h1  h2 a
Actualturbine work
T 


Isentropicturbine work ws h1  h2 s
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Draw the T-s diagram showing Turbine
Isentropic Efficiency.
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Derive cp = cv+ R from h = u + pv using the
ideal gas law
h = u+pv = u+RT
dh = du + RdT +TdR dR=0
dh/dT = du/dT + R
cp = cv + R
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What is Mach number?
V/a where a is the speed of sound
Using Gibbs equation Tds = du + pdv find
s = cv ln(T2/T1) + R ln(v2/v1).
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du pdv
dT
dv
ds 

ds  cv 
 R

T
T
T
v
 T2 
 v2 
s  cv ln   R ln 
 T1 
 v1 
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Find the following in terms of  using cp=cv+R
1) R/cv
R/ cv = (cp/ cv) - 1 =  - 1
2)R/ cp
R/ cp = 1 - (cv / cp) = 1 - (1/  ) = ( - 1)/ 
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3) (cv - R) / cp
(cv - R)/ cp = (cv / cp) - (R / cp) = 1/ - ( -1) / 
= (2- )/
4) (cv - R) / cv
(cv - R)/ cv = 1 - ( - 1) = 2 - 
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Use s = cp ln(T2/T1) - R ln(p2/p1) to find the
isentropic relationship for pressure and
temperature
cp ln(T2/T1) = R ln(p2/p1)
ln(T2/T1) = (R/cp ) ln(p2/p1)
raise “e” to this power
(T2/T1) = (p2/p1) (-1)/
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R/cp=(-1)/
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Use Tt=T+V2/(2gccp) to find Tt/T in terms of 
and Mach number
V = M a where a is SQRT(gc RT)
Tt=T+M2 RTgc /(2gccp)
(Tt/T) = 1 - M2 ( R)/(2cp)
R/cp=(-1)/
(Tt/T) = 1 - M2 (-1)/2
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