April 22, 2023 EGR 4347 2
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
April 22, 2023 EGR 4347 3
EGR 4347 - Review
Explain extensive and intensive properties.
Extensive depends on system
Intensive is independent of system
April 22, 2023 EGR 4347 4
EGR 4347 - Review
Give at least four forms of energy which make up the term total energy, E.
1. Thermal 2. Mechanical3. Potential 4. Electric5. Chemical 6. Nuclear7. Kinetic 8. Magnetic
April 22, 2023 EGR 4347 5
EGR 4347 - Review
Give the unit of mass in the SI, Old English and English Engineering system.
SI - kgOld English - lbm
English Engineering - slug
April 22, 2023 EGR 4347 6
EGR 4347 - Review
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.
April 22, 2023 EGR 4347 7
EGR 4347 - Review
What is the state postulate?
The state of a simple compressible system is completely specified by two independent, intensive properties.
April 22, 2023 EGR 4347 8
EGR 4347 - Review
What is a perfect or ideal gas (physical meaning)?No dissociation Intermolecular forces negligibleOccurs at low pressures and high temperatures (compared to critical point)
What is the ideal gas law?P = R T
April 22, 2023 EGR 4347 9
EGR 4347 - Review
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
April 22, 2023 EGR 4347 10
EGR 4347 - Review
Give the equation for and define Continuity.
outin mm..
April 22, 2023 EGR 4347 11
EGR 4347 - Review
Give the equation for and define 1st Law for a Control Volume.
outoutoutout
inininin
kepehmWQ
kepehmWQ
)(
)(...
...
April 22, 2023 EGR 4347 12
EGR 4347 - Review
Give the equation for and define the 2nd law for a Control Volume.
0TQSsmsmS
k
kgen
.
ee
.
ii
..
CV
April 22, 2023 EGR 4347 13
EGR 4347 - Review
Define adiabatic.No heat interaction.
Define reversible.A process that can be reversed without leaving any trace on the surroundings.
Define isentropic.ds=0
April 22, 2023 EGR 4347 14
EGR 4347 - Review
Is an adiabatic, reversible process isentropic?Yes
Is an isentropic process always adiabatic and reversible?No
Is an isentropic, adiabatic process reversible?Yes
April 22, 2023 EGR 4347 15
EGR 4347 - Review
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
April 22, 2023 EGR 4347 16
EGR 4347 - Review
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
April 22, 2023 EGR 4347 17
EGR 4347 - Review
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)
April 22, 2023 EGR 4347 18
EGR 4347 - Review
Explain the concept of isentropic efficiency as it applies to a turbine.
s21
a21
s
aT hh
hhww
workturbineIsentropicworkturbineActual
April 22, 2023 EGR 4347 19
EGR 4347 - Review
Draw the T-s diagram showing Turbine Isentropic Efficiency.
April 22, 2023 EGR 4347 20
EGR 4347 - Review
Derive cp = cv+ R from h = u + pv using the ideal gas law
h = u+pv = u+RTdh = du + RdT +TdR dR=0dh/dT = du/dT + Rcp = cv + R
April 22, 2023 EGR 4347 21
EGR 4347 - Review
What is Mach number? V/a where a is the speed of sound
Using Gibbs equation Tds = du + pdv finds = cv ln(T2/T1) + R ln(v2/v1).
1
2
1
2 lnlnvvR
TTcs
vdvR
TdTcds
Tpdv
Tduds
v
v
April 22, 2023 EGR 4347 22
EGR 4347 - Review
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)/
April 22, 2023 EGR 4347 23
EGR 4347 - Review
3) (cv - R) / cp
(cv - R)/ cp = (cv / cp) - (R / cp) = 1/ - ( -1) / = (2- )/
4) (cv - R) / cv
(cv - R)/ cv = 1 - ( - 1) = 2 -
April 22, 2023 EGR 4347 24
EGR 4347 - Review
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) R/cp=(-1)/raise “e” to this power(T2/T1) = (p2/p1) (-1)/