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High-PressureThermalPlasmasandSources(PlasmaSourcesII)TonyMurphy20thEuropeanSummerSchool,October2016“LowTemperaturePlasmaPhysics:BasicsandApplicaJons”MANUFACTURING
WhatisaThermalPlasma?Atorclosetoatmosphericpressure(atleast0.1atm)Temperature~1to2eV(10000to20000K)forelectronsandheavyspeciesHighlyionised(typically100%,atleast5%)HighelectrondensiDes(~1023m-3)Formedbydcoracelectricarcs,radio-frequencyormicrowaveelectromagneDcfieldsDominatedbycollisionsVerywidelyusedinmanufacturingandotherindustries• Highpowerfluxes• HighfluxesofreacDvespecies• StrongradiaDveemission
ThermalPlasmaApplicaJons:ArcWelding
ThermalPlasmaApplicaJons:PlasmaCuTng
ThermalPlasmaApplicaJons:PlasmaSpraying
ThermalPlasmaApplicaJons:WasteTreatment
ThermalPlasmaApplicaJons:ArcLighJng
Carbon arc lamp Xenon arc lamp
ThermalPlasmaApplicaJons:MineralProcessing
Electric arc furnaces
Aluminium dross recovery
Plasma remelting
ThermalPlasmaApplicaJons:CircuitBreakers
ThermalPlasmaApplicaJons:ICP-OES,ICP-MS
Inductively-coupled plasma – optical emission spectroscopy
Inductively-coupled plasma – mass spectroscopy
ThermalPlasmaApplicaJons:NanoparJcleSynthesisandParJcleSpheroidizaJon
ThermalPlasmasinNature:Lightning
TheFirstThermalPlasmaApplicaJon?
The Miller-Urey experiment
Outline1. ThermalplasmaproperDes
• Localthermodynamicequilibrium(LTE)• ComposiDon• ThermodynamicandtransportproperDes• RadiaDveemission
2. GeneraDonofthermalplasmas• Transferredarcs• Non-transferredarcs• RFinducDvely-coupledplasmas• Microwaveplasmas• Typesofplasmaflow
3. Modellingofthermalplasmas• EquaDons• Turbulence,electrodesheaths,gasmixtures
4. ThermalplasmadiagnosDcs• Enthalpyprobes• Emissionspectroscopy• LaserscaXering
5. ThermalplasmaapplicaDons• PlasmawastedestrucDon
CollisionsbetweenElectronsandIons
Ar+
Anode
Cathode
e
E Ar+
Anode
Cathode
e
E = =F qE
am m
CollisionsbetweenElectronsandHeavySpeciesTransferLiYleEnergy
Ar+
Anode
Cathode
e
E
Δ ≈kin 2 e hE m mAr+
Anode
Cathode
E e
LotsofCollisionsbetweenElectronsandIonsTransferALotofEnergy
Ar+
Anode
Cathode
e
E Ar+
Ar+
Ar+
Ar+
Ar+ e e
e e
e
e
e
e e
Ar+
Anode
Cathode
E
Ar+
Ar+
Ar+
e
e
e 6
5
For 15 000 K,1 atm:
3 10 m ~7 10 m/s
~ 5 ps
e e el vτ−
=
×
×
EffectofPressureonEquilibrium
Increasing pressure increases the number density, and therefore the collision rate and the transfer of energy from electrons to heavy species
LocalThermodynamicEquilibrium(LTE)LTEexistsifallspeciessaDsfy• MaxwelliandistribuDonfortranslaDonaltemperatures• BoltzmanndistribuDonforexcitaDontemperatures• ChemicalequilibriumequaDonsforreacDons,e.g.,ionisaDonandallthesetemperaturesarethesameLTEexistsifthecollisionrateismuchgreaterthantheratesofdiffusionandconvecDon
Itisgenerallyvalidinthebulkoftheplasma(awayfromtheedgesandelectrodes)
IfLTEexists,thenifweknow(atagivenpointintheplasma)
• thepressure• thetemperature(orinsteadthedensityofanyspecies)
• ifthereisamixtureofgases,theproporDonsofeachgases
thenwecanfullydescribethecomposiDonoftheplasmaatthatpoint
ThisgreatlysimplifiesmodellinganddiagnosDcs
0 5000 10000 15000 20000 25000 300001020
1021
1022
1023
1024
1025
1026
e-,Ar+
Ar3+
Ar2+N
umbe
r den
sity
(m-3)
Temperature (K)
Ar
Ar+
e-
WhyWeLoveLTE
Example: argon arc at 1 atm
WhyCalculatePlasmaProperJes?1.TheyareneededforcomputaJonalmodelling
( )
2
( ) 0
( ) ( )
where 2 ,etc
5( ) ( )2
where isafunctionof
0
rr r
p
B
pc c
h
t
Pt
v r
kh h h ht e
T
U κ
ρρ
ρρ ρ
ρ
τ
φ
η
σ
ρσ
∂+∇⋅ =
∂∂
+∇⋅ = −∇ −∇⋅ + × +∂
= − ∂ ∂
⎛ ⎞∂+∇⋅ = − −∇⋅ ∇ + ⋅∇⎜ ⎟⎜ ⎟∂ ⎝ ⎠
∇ ⋅ ∇ =
v
v vv τ
v
j B g
j j
WhyCalculatePlasmaProperJes?2.Measurementsareinaccurateandinadequate
0 5000 10000 15000 20000 25000 300000
1
2
3
4
5
6
Nitrogen, 1 atm
Temperature (K)
Ther
mal
con
duct
ivity
(W m
-2K
-1)
Calculated (Murphy) Measured (Hermann & Schade) Measured (Plantikow)
0 5000 10000 15000 20000 25000 300000.00000
0.00005
0.00010
0.00015
0.00020
0.00025
Nitrogen, 1 atm
Temperature (K)
Vis
cosi
ty (k
g m
-1s-
1 )
Calculated (Murphy) Measured (Guevara et al.)
ClassificaJonofProperJesThermodynamicproperDes• Massdensity(kg/m3)• Specificheatatconstantpressurecp(J/kg/K)• Specificenthalpy(J/kg)
TransportproperDes(transportcoefficients)• Viscosity(kg/m/s)• ThermalconducDvity(W/m/K)• ElectricalconducDvity(S/m)• Ordinarydiffusioncoefficient(m2/s)• Thermaldiffusioncoefficient(kg/m/s)RadiaDonproperDes• Netemissioncoefficient(W/m3/sr)
RelaJonbetweenBasicDataandMaterialProperJes
Species t hermo - d ynamic d ata
Binary collision integrals
Composition
Thermodynamic properties
Transport properties
Fluid dynamic equations
Basic data
Properties
PlasmaComposiJon
Useeither:• SahaequaDonsforionisaDonreacDons&Guldberg-WaageequaDonsfordissociaDonreacDons– Solvesimultaneously(oneequaDonforeachreacDon)
• MinimisaDonofGibbsfreeenergyG=H–TS(H=enthalpy,S=entropy)– RestricDons:chemicalelementsconserved,chargeneutrality– Inputdata(specificheatofeachspecies/parDDonfuncDonsforeachspecies)canbecalculatedfromspectraldata,ortakenfromtables
Examples
0 5000 10000 15000 20000 25000 300001020
1021
1022
1023
1024
1025
1026
e-,Ar+
Ar3+
Ar2+
Num
ber d
ensi
ty (m
-3)
Temperature (K)
Ar
Ar+
e-
0 5000 10000 15000 20000 25000 300001020
1021
1022
1023
1024
1025
Ar3+
N2+Ar2+
Num
ber d
ensi
ty (m
-3)
Temperature (K)
e-
Ar, N2N
N2Ar+
N+
Argon, 1 atm 50% Argon, 50% Nitrogen, 1 atm
ThermodynamicProperJes
TheseareeasilycalculatedoncetheplasmacomposiDonisknown
3
1
1
1
1 1
Density (kg m )
1Enthalpy (J kg ) (+ minor correction term)
Specific heat (J kg K )
N
i ii
N
i i ii
pP
n m
h nm h
hCT
ρ
ρ
−
=
−
=
− −
=
=
∂=∂
∑
∑
SpecificHeatforVariousPlasmas
0 5000 10000 15000 20000 25000 300000
50
100
150
200
250
300 Argon Nitrogen Oxygen Helium Hydrogen
Spe
cific
Hea
t (kJ
kg-
1 K-1)
Temperature (K)
EnthalpyforVariousPlasmas
0 5000 10000 15000 20000 25000 300000
200
400
600
800
1000
1200
1400
1600
1800
2000 Argon Nitrogen Oxygen Helium Hydrogen
Ent
halp
y (M
J kg
-1)
Temperature (K)
TransportProperJes
For plasmas, have many species present – need information about collision cross-sections between all pairs of species: • neutral-neutral • neutral-ion • neutral-electron • charged-charged (Coulomb)
• Viscosity: transport of momentum perpendicular to flow • Thermal conductivity: transport of heat • Electrical conductivity: transport of charge • Diffusion coefficients: transport of mass Determined by collision cross-sections (mean free paths) of all species
Viscosity
( )
( ) ( )
η
δ δ δ δ
=
=
= ∑
=∑
= ∑+
⎡ ⎤× − Ω + + Ω⎣ ⎦
102
000
1
0021
(1,1) (2,2)32
Tofirstorder:
where 5
163
5
B j jj
qij j i
j
qi i k k
ijkj i k
j ij jk k ij jkik ik
k T n b
Q b n
n m n mQ
m m m
m m
CollisionIntegralsareCalculatedfromtheIntermolecularPotenJals(using3integraJons)
( ) ( ) ( )( , ) ( )2 2 30
exp where 2 2
ijl s lsij ij ij ij ijij ij
ij
kTT Q g d gkTµ
γ γ γ γπµ
⌠⎮⌡
∞+Ω = − =
( )0
( ) 2 1 cosl lijQ g bdbπ
π χ⌠⎮⌡
= −
are averages over a Maxwellian distribution of the gas kinetic cross-section
02
2 2 212
( , ) 2(1 )
mrr
dr rb g bg b r
χ πµϕ
⌠⎮⎮⎮⌡
= −− −
intermolecular potential ϕ(r) reduced mass µ initial relative speed g impact parameter b
where the angle of deflection is
ViscosityforVariousPlasmas
0 5000 10000 15000 20000 25000 300000.0000
0.0001
0.0002
0.0003
0.0004
Argon Nitrogen Oxygen Helium Hydrogen
Vis
cosi
ty (k
g m
-1s-
1 )
Temperature (K)
Viscosity describes relationship between shear stress and velocity gradient
, is collis~ ion cross e n s ctio
x
i
dvFdy
mT
η η
η
= −
ΩΩ
ThermalConducJvityforVariousPlasmas
0 5000 10000 15000 20000 25000 300000
2
4
6
8
10
12
14 Argon Nitrogen Oxygen Helium Hydrogen
Ther
mal
Con
duct
ivity
(W m
-1K
-1)
Temperature (K)
Thermal conductivity describes relationship between heat flux density an
~
d temperature gradient
, is collision cross-secti onp ii
dTk q kdx
C Tkm
= −
ΩΩ
ComponentsofThermalConducJvityforNitrogen
0 5000 10000 15000 20000 25000 300000
1
2
3
4
5
6 Total Heavy species Reaction Electron Internal
Ther
mal
Con
duct
ivity
(W m
-1K
-1)
Temperature (K)
ElectricalConducJvityforVariousPlasmas
0 5000 10000 15000 20000 25000 300000
2000
4000
6000
8000
10000
12000
14000
16000
Argon Nitrogen Oxygen Helium Hydrogen
Ele
ctric
al C
ondu
ctiv
ity (S
m-1)
Temperature (K)
Electrical conductivity describes relationship between current density and voltage gradient
, is electron density, is density of other species, is collision cross sectio n~ e e
dVjdx
n n nTn
σ σ
σ
=
ΩΩ
RadiaJveEmissionImportantinthermalplasmasAfulltreatmentisdifficult:• DetermineemissionandabsorpDonateveryvolumeelement
• AlargenumberofwavelengthintervalsrequiredtocoverlineandconDnuumradiaDon
NetemissioncoefficientsareaverysuccessfulapproximaDon• Foragiventemperature,integrateemissionoverallwavelengths
• TakeintoaccountabsorpDoninasphereofagivenradius
ForapplicaDonsinwhichradiaDonfluxatboundaryisimportant,needmorecomplextreatments
J. J. Lowke J Quant Spectrosc. Radiat. Transf. 16 (1974) 111 A. Gleizes et al. J. Phys. D: Appl. Phys. 26 (1993) 1921
NetEmissionCoefficientsforArgonat1atm
L is the radius of the absorbing sphere J. A. Menart PhD Thesis Uni. of Minnesota (1996)
2.GeneraJonofThermalPlasmasa)ElectricArcs:TransferredArcs
• Arcbetweenoneelectrode(usuallycathode)andmetalorconducDngworkpiece
• Highenergytransferefficiencytoworkpiece• Lowgasflow• RelaDvelyinexpensive• Highpeaktemperature,narrowdistribuDon(highgradients)• Usedinwelding,plasmacuing,electricarcfurnaces,arclamps,
wastedestrucDon,etc.
b)ElectricArcs:Non-transferredArcs
• Arcisconfinedwithinplasmatorch• HighefficiencyheaDngofbulkgas(“archeater”)• Highgasflow• BroaderheatfluxdistribuDon,lowerpeaktemperature• Usedinplasmaspraying,wastedestrucDon,etc.
c)RFInducJvely-CoupledPlasmas
• Noelectrodes,solowcontaminaDon• Generatesalarger,moreuniform,plasmavolume• Moreexpensive;lowerefficiency• MoresensiDvetoprocessvariaDons• Usedforpowderprocessing(densificaDon,spheroidisaDon),
nanoparDcleproducDon,etc.
d)MicrowavePlasmas
• No electrodes • Several different designs • Relatively small and expensive • Strongly non-equilibrium (gas temp. < 5000 K, electron temp. > 10 000 K • Applications include MP-AES (microwave plasma - atomic emission spectroscopy),
gas treatment
TypesofPlasmaFlowGravity-drivenflow• Lowcurrent(<20A)arcs• Flowdrivenbybuoyancy• Arclamps
FlowdrivenbyjxBforces• Highercurrent(>30A)arcs• Pressuregradient=jxB(themagneDcpincheffect)
• MaximumvelociDesfrom100to1000m/s
• Arcsforwelding,plasmacuing,etc
j
MagneJcPinch(LorentzorjxB)Force
B F
TypesofPlasmaFlowFlowsdrivenbythermalexpansion• Inplasmatorches,thearcoccursinaconfinedregion,causingthepressuretorise
• SupersonicvelociDes(over2000m/s)typicallyachieved• Arcstabilisedbyhighgasflowandopenswirlofgas• Typicalinplasmaspraying
Shock diamonds indicating supersonic flow
3.ModellingofThermalPlasmas• UsecomputaDonalfluiddynamicequaDonsforviscous
incompressibleflow• AconservaDonofenergyequaDonisrequiredbecausethe
temperatureisnotconstant• Maxwell’sequaDonsareusedtodescribecurrentconDnuity
(chargeconservaDon)andmagneDcfields• AddiDonaltermsdescribing‘plasma’effectsareincluded(ohmic
heaDng,radiaDveemission,magneDcpincheffect,electrondiffusion)
• TheequaDonofstateisimplicitinthedependenceofthermophysicalproperDesontemperature
• ModificaDonsrequiredforelectroderegions,turbulentflows,departuresfromLTE,highMachnumberflow,etc.
ConservaJonEquaJons:SingleGas
( )
2
02
( )
( )
( )
0
52
0
( )
(
)
B
p
κ
P
kU
t
t
ch h
eht
T
ρ
σ
ρ
ρ
ρ
ρ
ρ
µσ φ
ρ
∇⋅
⎛ ⎞∇ ⋅ ∇ +⎜ ⎟⎜ ⎟⎝ ⎠
+ =
+ = − − + +
∇⋅ ∇
+ = − − +
=
∂∇⋅
∇ ⋅
∇ ⋅
∇ ×
⋅
∂∂
∂
∂
∂
= −∇
∇
v
vv
v
j B g
j
v
j
τ
A j
Time-dependent term Convective term Diffusive term Source term
ConservaJonofMass(MassConJnuity)
0
mass density time velocity
Note: if there is a source of mass (e.g., evaporation of a surface) then a source term is re u ed
(
q ir
)t
t
ρρ
ρ∂
∇⋅+∂
=
v
v
ConservaJonofMomentum
where
mass density, time, velocity viscous stress tensor, visco
2
sity pressure current de
( )
2 ,
(
nsity, a
,
)
3
m
ji iii iji j i
P
vv v i jx x
t
t
P
x
ρ
ρ
η
η
ρ
τ τ
ρ
η
∇⋅
⎛ ⎞∂⎛ ⎞∂ ∂= − ∇⋅ = + ≠⎜ ⎟⎜ ⎟ ⎜ ⎟∂ ∂ ∂⎝ ⎠
∇ ×+ = − − +∇
⎝ ⎠
+∂
⋅∂ τ
v
vv
τ
g
j
v
B
B
v
j
gnetic field strength acceleration due to gravityg
Magnetic pinch force
Gravity
Pressure gradient
ConservaJonofEnergy2
mass density, time, velocity, temperature enthalpy, thermal conductivity, speci
(
fic heat
current density, electr
5
ical conductivity
(2
))
p
B
p
kht
U Te
t Th c
h κc
U
h
ρ
κ
ρσ
σ
ρ∇ ⋅∇⎛ ⎞
∇ ⋅ ∇ +⎜ ⎟⎜+ = − − +
∂⋅
⎟⎝∂ ⎠
j j
v
j
v
radiative emission coefficient Boltzmann constant, elementary chargeBk e
( )
For compressible flow (Mach number > 0.5), need to add
. , where , to right-hand sideDp Dp p pDt Dt t
∂− ⋅∇ + ≡ + ⋅∇
∂τ v v
%
Ohmic heating
Radiative cooling
Electron diffusion
ChargeConJnuity,MagneJcPotenJal,Maxwell’sEquaJons
( )2
0
0
0
electrical conductivity, electric potential magnetic potential, current density permeability of free space
0
σ φ
µ
σ φ
µ
σ
µ
φ∇ ⋅ ∇
∇
=
= −
= − ∇
∇× =
jB j
A
A
j
j
ComplicaJons:TurbulenceManythermalplasmaflowsareturbulent• Plasmajets(e.g.,forplasmaspraying)• PlasmacuingarcsDifferentapproaches• DirectnumericalsimulaDon(DNS)
– Solvesallthescalesofflow– Veryexpensive,andunfeasibleforindustrialproblems
• LargeeddysimulaDon(LES)– Solvesforlargescalesandapproximatelymodelssmallscalesoftheflow– Turbulencemodelneededtoapproximatethesmallscales
• Reynolds-averagedNavier-Stokes(RANS)– Approximatelymodelsallscalesoftheflow– Themostcommonapproachforindustrialproblems– Include:
– 0equaDons:Prandtlmixinglength– 1equaDon:Spalart-Allmaras– 2equaDons:K-ε,K-εRNG,K-ω
TheK-εModelTurbulenceismodelledasanaddiDonaldiffusionmechanismSolveaddiDonaltransportequaDonsforK(turbulencekineDcenergy)andε(turbulenceenergydissipaDon),whichthengiveviscosityandthermalconducDvity
2
1 2
2
2
1
( ) ( ) 2
( ) ( ) 2
2
is turbulent viscosity, is turbulent thermal conductivityPr
, , ,
t
K
t
Tt
t pt t
t
K
K K K Gt S
C G Ct S K K
G
CKC
S S C
ε
η
ε
ηρρ η ρε
ηρε ε ερ ε η ε ρ
η
ηη ρ κ
ε
⎡ ⎤⎛ ⎞∂+∇⋅ =∇⋅ + ∇ + −⎢ ⎥⎜ ⎟
∂ ⎝ ⎠⎣ ⎦
⎡ ⎤⎛ ⎞∂+∇⋅ =∇⋅ + ∇ + −⎢ ⎥⎜ ⎟
∂ ⎢ ⎥⎝ ⎠⎣ ⎦
= ∇ +∇
= =
v
v
v v
2, Pr are constantstC
EffectofTurbulence
Mass fraction of air for argon plasma jet discharging into air A. B. Murphy and P. Kovitya, J. Appl. Phys. 73 (1993) 4759
Laminar
Turbulent
Argon
Air
Argon
Air
EffectofTurbulence
Temperature (1000 K) of argon plasma jet discharging into air A. B. Murphy and P. Kovitya, J. Appl. Phys. 73 (1993) 4759
Laminar
Turbulent
Ar plasma jet into Air T (K): 300 12,000
ω (s-1): -50,000 50,000
Temperature
Vorticity
(mm)
captures small~large eddies.
Pfender et al. (1991)
(2D-axisym)
Eddy-breakup
Eddy-breakup
Direct numerical simulation
(mm)
Courtesy Dr Masaya Shigeta, Osaka University
ComplicaJons:ElectrodeSheathRegions
10-1 mm 10-5 mm
Te > Th ne ≠ ni
AnodeTreatments
( ) ( )*2 * 30 0
the temperature adjacent to the anode is low, so if assume LTE, then 0 0
Add electron diffusion term (Sansonnens et al.)
0
and ar
Problem:
Approach
el
1:
e
e
a e e e e
e
e a
e
n
D
e
n n n n n n
D
D n
D
σ
σ φ
α
≈ ⇒ ≈
= − ∇ +
∇⋅ ∇ + − =
∇j
ectron and ambipolar diffusion coefficients is three-body recombination coefficient, * indicates LTE value
"LTE-diffusion approximation" (Lowke and Tanaka)Set mesh size near anoApp
de roach
to 2:
width
α
of region in which electron diffusion dominates ( 0.1 mm).Then use LTE everywhere.
Bk T eEΛ = ≈
L. Sansonnens, J. J. Lowke and J. Haidar J. Phys. D: Appl. Phys. 33 (2000) 148 J. J. Lowke and M. Tanaka J. Phys. D: Appl. Phys. 39 (2006) 3634
ComparisonofApproaches1and2
(Sansonnens et al)
(Lowke & Tanaka)
Anode
ThermionicCathodeTreatment
• Applies to high melting point materials e.g., W, C, Mo, Zr • Electrons emitted from cathode • Cathode heated through ion bombardment • Current densities around 100 A/mm2
( )25 2 2
Richardson equation
6 10 A mm K for most metals (work function) 4.5 V for W
exp
2.5 V for W(Th)
w B
w
j AT k
A
e Tφ
φ
− −≈ ×
≈
−
≈
=
ThermionicCurrentDensityvsTemperature
Decreasing work function by 2 V reduces the cathode temperature by 1700 K (for 100 A mm-2) Metals that don’t have high melting points (Cu, Al, Fe etc) cannot be thermionic emitters
0 1000 2000 3000 4000 500010-6
10-4
10-2
100
102
104
106
Cur
rent
den
sity
(A m
m-2
)
Temperature (K)
φw = 4.5 V φw = 2.5 V
ComplicaJons:PlasmasinGasMixturesIfmorethanonegaspresent,thesegasescanmixordemix
EveninLTE,needtoknowtheirrelaDvefracDons
Foreachspeciesi
( ) ( )
2
1
: mass fraction : reaction source term : diffusion mass flux
: ordinary diffusion coefficient
: thermal diffusion coefficient: mole
l
fr
n
ρ ρ
ρ =
∂ +∇⋅ = −∇⋅ +
= ∇ − ∇∑
i i i i
q Tii j ij j
i i
i
ijTi
i
i
j
Y dt Y r
n
Y
m m D x D
r
D
Dx
T
v J
J
J
action
A. B. Murphy J. Phys. D: Appl. Phys. 34 (2001) R151
CombinedDiffusionCoefficients
Groupspeciesintogases
E.g.,forAr-Hearc
• argongas=Ar,Ar+,Ar2+,Ar3+,e-
• heliumgas=He,He+,He2+,e-
Modeldiffusionofheliumgasthroughargongas
Typically50ordinaryandthermaldiffusioncoefficientsreplacedbytwocombineddiffusioncoefficients
ExactforhomonucleargasesthatdonotreactforplasmasinLTE
GasConservaJonEquaJon
SpeciesconservaDonequaDonsforeachspecies(Ar,Ar+,
Ar2+,Ar3+,He,He+,He2+,e-)
( )i i iY rρ∇⋅ = −∇⋅ +v Jreplaced by a single gas conservation equation
( ) ( )( )Ar Ar Ar
2Ar Ar He Ar,He He Ar/ ln
x T
Y t Y
n m m D x D T
ρ ρ
ρ
∂ ∂ +∇⋅ = −∇⋅
= ∇ − ∇
v J
J
The overbarred quantities are averaged over all species A. B. Murphy Phys. Rev. E 48 (1993) 3594
Combined diffusion coefficients
Example:DemixinginanArgon-HeliumArc
A. B. Murphy Phys. Rev. E 55 (1997) 7473
Example2:MetalVapourinWeldingArc
All emission Atomic iron line Atomic argon line
Argon arc with steel wire
GoeckeSF,MetzkeE,Spille-KohoffAandLangulaM2005ChopArc.MSG-LichtbogenschweißenfürdenUltraleichtbau(StuXgart:FraunhoferIRB)
MeasurementsShowaRelaJvelyCoolArc,andaLocalTemperatureMinimumonAxis
ZielińskaS,MusiołK,DzierżęgaK,PellerinS,ValensiF,deIzarraC,BriandFPlasmaSourcesSci.Technol.16832–8(2007)
Current = 326 A Steel wire 6 mm above workpiece 4.5 mm above workpiece 3 mm above workpiece
ModellingIndicatesCoolingCanOccurduetoIncreasedRadiaJveEmissionfromMetalVapour
SchnickM,FüsselU,HertelM,Spille-KohoffAandMurphyABJ.Phys.D:Appl.Phys.43022001(2010)
5000 10000 15000 20000 25000100101102103104105106107108109
1010
Net
em
issi
on c
oeffi
cien
t (W
m-3
sr-1
)
Temperature (K)
1% Fe, 99% Ar 1% Al, 99% Ar 100% Ar
4.ThermalPlasmaDiagnosJcsProbes• Langmuirprobes• EnthalpyprobesSpectroscopy• Emissionspectroscopy• AbsorpDonspectroscopyLaserscaXering• ElasDcscaXering
– RayleighscaXering– ThomsonscaXering– RamanscaXering
• InelasDc– LIF(laser-inducedfluorescence)– Two-photonLIF– CARS(coherentanD-StokesRamanscaXering)
EnthalpyProbesShut-off valve
Coolant in
Coolant out
( ) ( )( )stagnation atm
water gas flow no gas flow
2
Enthalpy Flow velocity
is cooling water mass flow rate is gas sampl
ing w
w
g
pg
P Pmh
m
T v
m
C Tm Tρ
−= Δ −Δ =
&&
&&
mass flow rate
Can also measure composition using gas analyser
EnthalpyProbeResults
Entrained air %, temperature (K) and velocity (m/s) for enthalpy probe (●) and laser scattering (Δ) Plasma torch, 900 A, argon, 2 mm downstream from orifice J. C. Fincke, S. C. Snyder, W. D. Swank, Rev. Sci. Instrum. 64 (1993) 711
OpJcalEmissionSpectroscopy
x
Arc
EmissionSpectroscopy:DeterminingtheTemperature
( ) ( )( )
Intensity exp
is energy of upper levelA is transition probability
is statistical weight of upper level is transition frequency
is number density of species (e.g.
mmn m mn
B
m
mn
m
mn
n T ES T A g hZ T k T
E
g
n
ν
ν
⎛ ⎞= −⎜ ⎟
⎝ ⎠
atoms) is partition function of speciesZ
The measurement system has to be calibrated Three standard methods: 1. Use a calibrated radiation source 2. Use ratio of intensity of two or more lines 3. Fowler-Milne method – use maximum in S(T)
m
n
hνmn
LaserScaYeringLightisscaYeredfromelectrons–bothbound(toatomsorions)andfreeTheintersecJonofthelaserbeamandtheobservaJonaxisdefinesapoint
scattered laserλ λ=laser transitionElastic scattering: λ λ≠
Thomson scattering: elastic scattering from free electrons Rayleigh scattering: elastic scattering from bound electrons Raman scattering: elastic scattering from bound electrons
scattered laserλ λ≠Resonance scattering: inelastic scattering from bound electrons
Laser-induced fluorescence: inelastic scattering from bound electrons
laser transitionInelastic scattering: λ λ=
scattered laserλ λ≠
scattered laserλ λ=
+
_ Dipole oscillates with E field; emits perpendicular to oscillation axis
ThomsonScaYeringSpectrum of scattered light depends on Te and ne Approach 1. Wavelength-resolved scattering: Measure scattered light as a function of wavelength – need to be careful of heating the plasma! Approach 2. Integrated scattering: No wavelength resolution Accept all light in a given range of wavelengths around laser wavelength
LaserScaYering:Wavelength-ResolvedScaYering
M. Kuhn-Kauffeldt, J.-L. Marques, J. Schein, J. Phys. D: Appl. Phys. 48 (2015) 012001
Sca
ttere
d si
gnal
Wavelength (rel. to laser wavelength) (nm)
T (1
04 K
)
n e (1
023 m
-3)
r (mm)
LaserScaYering:IntegratedScaYeringRayleighscaXering(elasDcscaXeringfromatoms/ions)ThomsonscaXering(elasDcscaXeringfromfreeelectrons)ResonancescaXering(inelasDcscaXeringfromatoms/ions)
100 A argon arc: T vs r
Spectroscopy
Laser scatt.
A. B. Murphy and A. J. D. Farmer, J. Phys. D: Appl. Phys. 25 (1992) 634
Ar ion laser – 514.5 nm
5.ThermalPlasmaApplicaJonsArcweldingPlasmasprayingPlasmacuingMineralprocessing• Arcfurnaces• PlasmaremelDngPlasmaspheroidisaDonArclighDngCircuitinterrupDonChemicalsynthesisProducDonofnanostructuredmaterials• NanoparDcles• Bulknanostructuredmaterials• Carbonnanomaterials(nanotubes,graphene,etc.)Plasmawastetreatment
PlasmaWasteTreatmentComparedtohigh-temperatureincineraDon,plasmagives:
HighertemperatureandenergydensiDes• ShorterresidenceDmes• Morecompactsystems
Heatsourceisindependentofwaste• Exhaustgasflowdecreased• Rapidshut-offpossible
Nolowerlimitonsize• EasyintegraDonintoprocesses• On-sitedestrucDonpossible
BUT:
Highcost
ComponentlifeDmescanbelimited
Highpowerplasmasourcedifficulttomake
J. Heberlein and A. B. Murphy J. Phys. D: Appl. Phys. 41 (2008) 053001
TrendfromNichetoMainstreamApplicaJons
Highly-concentratedwastesorwastesrequiringhightemperatures:Asbestos-containingwastes
Incineratorfly-ashandgrate-ash
Ozone-depleDngsubstances
Otherconcentratedchemicals
Generalwastes:Municipalsolidwastes
Medicalwastes
Auto-shredderresidues
Tyres
Sewagesludge
WesJnghousePlasma:WasteTreatment&FuelProducJon
DCplasmatorch,upto2.5MW
TreatMSW,auto-shredderresidue,industrialliquidandsolidwastesPlantscapaciDesfrom25to300tonnesperday
E.g.,EcoValleyUtashinai,Japan:165tauto-shredderwasteperday,8MWelectricalpowerfromburningsyngas(CO+H2)produced
PLASCON
Treatsliquidandgaseouswastestreams
150kWnon-transferredarc10plantsinAustralia,Japan,USA,Mexico
Treats• Ozone-depleDngsubstances• PCB-contaminatedoils• Greenhousegases• Liquidorganicwastes
A. B. Murphy, T. McAllister, Appl. Phys. Lett. 73 (1998) 459
FluorocarbonGreenhouseGasesareFormedasaBy-productofHCFCProducJonHFC-23=CHF3=trifluoromethane
GlobalwarmingpotenDalof11700
ByproductofCHClF2(HCFC-22)producDon(2.4%bymass)
185tonne/yearproducedatQuimobasicosSAdCV,Monterrey,Mexico+ → + + +3 2 2 36HF 2CHCl CHCl F CHClF CHF 6HCl
185tonnesperyearofHFC23 is equivalent to 2.2 million tonnes per year CO2
i.e., the annual emissions from a 300 MW coal-fired power station
a 600 MW gas-fired power station
or 500 000 cars
TrifluoromethaneisSuccessfullyDestroyedByPLASCON
+ + → +13 2 2 22CHF H O O CO 3HF
PLASCONDestrucJonofHCF23isVeryProfitable
Economics (under Kyoto Protocol Clean
Development Mechanism): Destruction of 1 t HCF 23
• Equivalent to destruction of 11 663 t CO2 • Carbon credits (@ $10/t CO2) have value of $120
000 • Cost of destruction < $10 000
185 t/year gives a profit of ~$20M/year
Carbon accounting: Destroying 1 t HFC 23
Destroys equivalent of 11 700 t CO2 Produces direct emissions of 0.6 t and indirect emissions of 6 t CO2
ThankyouCSIROManufacturingTonyMurphyChiefResearchScienDstt +61294137150e [email protected] www.csiro.au
MANUFACTURING