20030902
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Transcript of 20030902
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Heat and Thermodynamics
Introduction
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Definitions! Internal energy
! Kinetic and potential energy! Joules
! Enthalpy and specific enthalpy! H= U + p x V! Reference to the triple point! Engineering unit ! H is the work done in a process! J, J/kg
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More Definitions
! Work! Standard definition W = f x d! In a gas W = p x V
! Heat! At one time considered a unique form of
energy! Changes in heat are the same as changes
in enthalpy
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Yet more definitions! Temperature
! Measure of the heat in a body! Heat flows from high to low temperature! SI unit Kelvin
! Entropy and Specific Entropy! Perhaps the strangest physics concept! Notes define it as energy loss! Symbol S! Units kJ/K, kJ/(kgk)! Entropy increases mean less work can be done by
the system
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Sensible and Latent Heat! Heat transfers change kinetic or
potential energy or both! Temperature is a measure of kinetic
energy! Sensible heat changes kinetic (and
maybe potential energy)! Latent heat changes only the potential
energy.
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Sensible Heat
! Q is positive for transfers in! c is the specific heat capacity ! c has units kJ/(kgC)
)( if ttcmQ =
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Latent Heat
! Heat to cause a change of state (melting or vaporization)
! Temperature is constant
m
v
lmQlmQ==
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Enthalpy Changes
! Enthalpy changes take into account both latent and sensible heat changes
hmQ =
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Thermodynamic Properties of H2O
TemperatureC
Specific enthalpy
100C
SuperheatedSteam
Latent heat
Wet steam
Sensible heat
Subcooledliquid
Saturatedsteam
Saturatedliquid
Saturation temp
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Pressure Effects
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Laws of Thermodynamics
! First Law! Energy is conserved
! Second Law! It is impossible to convert all of the heat
supplied to a heat engine into work! Heat will not naturally flow from cold to hot! Disorder increases
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Heat Transfer
Radiation
4TAQ
Conduction
TlAkQ =
l
AT1T2
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More Heat Transfer
Convection
Mass Flow
TAhQ =
Condensation
Latent heat transfer from vapor
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Daltons Law
If we have more than one gas in a container the pressure is the sum of the pressures associated with an individual gas.
...321 +++= PPPPc
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Condensing Heat Exchanger
CoolantIn
CoolantOut
SteamIn
WaterOut
P
T
P=PsaturationT=Tsaturation
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Non-Condensables in Heat Exchanger
CoolantIn
CoolantOut
SteamIn
WaterOut
P
T
P=Psaturation+PgT=Tsaturation
Condenser AppearsSubcooled
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For You to do
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HTS Normal Operation
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Reactor Thermal Power
Fuelbundle/
HTS
Moderator
End shield/shield tank
QSCQM
Bleed cooler
Boiler
PreheaterBoiler
blowdown
Feedwater
HT pump
2nd stage Reheatdrains
Steam toturbine
Feed & bleedQL
Pipingloses
QP
QHT
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Reactor Power and T
! T is an indicator of reactor power if boiling is not taking place
TcmQ =
! At boiling T stops changing! In boiling channels total enthalpy
increase must be calculated
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Fuel Safety
! No overpowering! Adequate cooling
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Fuel Heat Transfer
D
A
Critical heat flux
Singlephase
convection
Nucleateboiling Partial film boiling Full film boiling (dryout)
S
u
b
c
o
o
l
e
d
b
o
i
l
i
n
g
S
a
t
u
r
a
t
e
d
(
b
u
l
k
)
b
o
i
l
i
n
g
Tsheath = Tsat
L
o
g
(
h
e
a
t
f
l
u
x
)
CF
Log (Tsheath Tcoolant)
B
Tcoolant = Tsat
E
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Two new terms
! Critical Heat Flux! CHF! The maximum heat flux nucleate boiling
can transfer
! Dryout! When dry patches of vapor exist on the
fuel sheath
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Uniform Heating
Inlet Outlet
Tcoolant
Single-phase
convection
Subcoolednucleateboiling Saturated nucleate (bulk) boiling Dryout
Tsheath surface
Tsat
Fuel element
Coolant
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Factors Affecting CHF
! Coolant Sub-cooling! Vapour Quality! Coolant Velocity
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Actual and Critical Heat Flux
Channel distance
C
h
a
n
n
e
l
p
o
w
e
r
inlet outlet
CHF
Actual h
eat flux
Bundles in dryout
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Critical Channel Power
! CCP! The minimum channel power that gives
dryout! Varies with coolant conditions! Varies with flux shape
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Boiling and Flow
Inlet OutletChannel position
9.6
9.8
10.0
10.4
10.2Boiling starts
Non-boiling mode
Boiling mode
P
r
e
s
s
u
r
e
M
P
a
(
a
)
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Temperature Profile2800
2400
2000
1600
1200
800
400
T
e
m
p
e
r
a
t
u
r
e
,
C
Fuel melting point
Fuelsheath
Coolant
Fuelsheath
Coolant
Fuel pellet
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More Temperature Profiles
Overratingand dryout
2400
2000
1600
1200
800
400
T
e
m
p
e
r
a
t
u
r
e
,
C
FuelsheathCoolant
Fuelsheath Coolant
Fuel pellet
Fuel meltingpoint
Nominal rating,normal cooling
Overratingwithout dryout
Light loadand dryout
2800
Possible film ofgaseous fission
products (on LOCA)
Vapour filmdue to dryout
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Bad things to do to fuel
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Low HTS Pressure
Tsat at reduced pressure
Tsat at normal pressure
Coolanttemperature at
reducedpressure
Channel position
C
o
o
l
a
n
t
t
e
m
p
e
r
a
t
u
r
e
Inlet Outlet
CHF at reducedpressure
CHF at normal pressure
Channel position
H
e
a
t
f
l
u
x
Inlet Outlet
a) Temperature profile
b) Heat flux profile
Actual hea
t flux
Coolant temperature atnormal pressure
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Reduced FlowSaturation temperature
Reduced flow
Normal flow
a) Temperature profile
Channel position
C
o
o
l
a
n
t
t
e
m
p
e
r
a
t
u
r
e
Inlet Outlet
Outlet
CHF at reducedflow
CHF at normal flow
Channel position
H
e
a
t
f
l
u
x
Inletb) Heat flux profile
Actual hea
t flux
Dryout zone
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Inlet High Temperature
Saturation temperature
High inlettemperature
Normal inlettemperature
Channel position
C
o
o
l
a
n
t
t
e
m
p
e
r
a
t
u
r
e
Inlet Outlet
CHF at high inlettemperature
CHF at normal inlet temperature
Channel position
H
e
a
t
f
l
u
x
Inlet Outlet
a) Temperature profile
b) Heat flux profile
Actual hea
t flux
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Flux Tilt to Outlet
Saturation temperature
Channel position
C
o
o
l
a
n
t
t
e
m
p
e
r
a
t
u
r
e
Inlet Outlet
CHF at skewed flux
CHF at normal flux
Channel position
H
e
a
t
f
l
u
x
Inlet Outlet
a) Temperature profile
b) Heat flux profile
Normal he
at flux
Normal flux
Skewed heat
flux
Skewed flux
Dryoutzone
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Flux Tilt to Inlet
Saturation temperature
Channel position
C
o
o
l
a
n
t
t
e
m
p
e
r
a
t
u
r
e
Inlet Outlet
CHF at skewed fluxCHF at normal flux
Channel position
H
e
a
t
f
l
u
x
Inlet Outlet
a) Temperature profile
b) Heat flux profile
Normal he
at flux
Normal flux
Skewed heat
flux
Skewed flux
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Excessive Channel Power
Saturation temperature
Channel position
C
o
o
l
a
n
t
t
e
m
p
e
r
a
t
u
r
e
Inlet Outlet
CHF at excessivechannel power
CHF at normal channel power
Channel position
H
e
a
t
f
l
u
x
Inlet Outlet
a) Temperature profile
b) Heat flux profile
Normal he
at flux
Normal channelpower
Excessivechannel power
Dryout zone
Excessiveheat flux
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For You to do
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HTS Components
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HTS Feed & Bleed
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BleedCondenser
! Non-condensable gases! Reduce heat transfer! Steam pressure rises! Increased reflux
cooling! Vessel appears sub
cooled
! Degassing Orifice
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Pressurizer Control
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Boiler Shrink and Swell
! Boilers are probably more correctly called steam generators
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Steady State Shrink and Swell
Zero Load Low Load Full Load
Rise inLevel
Rise inLevel
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Transient Shrink and Swell
! Shrink and swell from short term effects! Reactor power boiler level
! Boiling increases
! Boiler Pressure boiler level ! Water flashes to steam! Steam expands
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Effects on the Downcomer! Water flow into the
annulus increases! Water flow out of
the annulus decreases
! Instrumentation sees a level increase
ExpansionForces
CycloneSeparators
DowncomerAnnulus
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Boiler Level Control
SwellMargin
ShrinkMargin
SwellMargin
ShrinkMargin
Constant Level Full Power Level
Zero Power Level
Fixed Level Control Ramped Level Control
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Improper Level! Low
! If tubes are uncovered! Reduce heat transfer! Time in loss of feedwater events is reduced! Reactor power automatically reduced
! Setback or stepback and finally a trip
! High! High vapor content in steam! Slugs of water to turbine! Turbine trip
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Boiler Pressure
! Boiler pressure is the key parameter in matching heat source to sink
! Reactor Leading! Reactor Lagging
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Warm-up and Cool-down
! Heat transfer in the boiler
mTAUQ =
! A low power levels the HTS is about the same temperature as the boiler
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Rx for Warm-up
! Put some energy into HTS from pumps and reactor power
! Increase boiler pressure! Boiler temperature follows (saturated
vessel)! HTS temperature follows that
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Rx for Cool-down
! Heat sources are pumps and decay heat! Boiler pressure is ramped down ! Steam energy released is greater that
energy input! Down go temperatures! Limit around 130-150C due to huge
volume of steam required
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Ideal Temperature Ramps
! 2.8C a minute! This rate minimizes
! Thermal stress! Probability of delayed hydride cracking! Feedwater loss
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For You to do
Heat and Thermodynamics COURSEHeat and Thermodynamics Presentation