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COMSOL CONFERENCE - Hannover – November 4th-6th 2008

Modeling of a Dielectric Barrier Discharge Lamp for

UV Production

Modeling of a Dielectric Barrier Discharge Lamp for

UV Production

S. Bhosle1,2, R. Diez1,2, H. Piquet1,2, D. Le Thanh1,2, B. Rahmani1,2, D. Buso1,2

1 LAPLACE, Université de Toulouse; UPS, INPT; LAPLACE (Laboratoire Plasma et Conversion d'Energie); 118 route de Narbonne, F-31062 Toulouse cedex 9, France.2 CNRS; LAPLACE; F-31062 Toulouse, France.Université de Toulouse, 118 route de Narbonne, 31062 Toulouse cedex 9, France

Presented at the COMSOL Conference 2008 Hannover

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OutlineOutline

Introduction- What is an Excilamp?- Dielectric Barrier Discharges (DBD)- Applications of Excilamps

Model Description- Equations used- Boundary Conditions

Obtained results- Influence of the Power Supply Mode- Influence of External Elements- Tool for Efficient Power Converter Design

Conclusion

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E

R(1S0) + R(1S0)

R

hυ

R*2R(1S0) + R(3P2)

R(1S0) + R(3P1)

1Σg+ 3Σu

+

1Σu+

R+R

R+R*

Excimer: contraction of "Excited Dimer"

What is an Excilamp?What is an Excilamp?

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What is an Excilamp?What is an Excilamp?

Energy (x103cm-1)

68

65

2

0

3 4 5 R(Å)

01

13 SP +

01

23 SP +

u1

u1+Σu

1+Σu

3

+Σg1

01

01 SS +

2ndcontinuum173nm

1stcontinuum147nm

147nm

+g0

126Inte

nsi

ty (

a.u

.)

~10nm

Wavelength (a.u.)

Continua:1st 2nd

Excilamp:

-Excimer Lamp

Or

-Exciplex Lamp

(http://www.physics.mq.edu.au/~rmildren/DBDs.html)

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H.T.

Hig

hvo

ltage

gen

erat

or

DielectricDischargegap

Electrode

Electrode

H.T.

Discharge

H.T.

Hig

hvo

ltage

gen

erat

or

DielectricDischargegap

Electrode

Electrode

H.T.

Discharge

DBD: different geometriesDielectric Barrier Discharges (DBD) various geometries

What is an Excilamp?What is an Excilamp?

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What is an Excilamp?What is an Excilamp?

UV

UV

H.T.

Hig

hvo

ltage

gen

erat

or

Ground grid

Internal electrodeExternal tube

Internal tube

Cooling fluid

Discharge gap

DBD: the axisymetric geometry (coaxial)

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What is an Excilamp?What is an Excilamp?

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Applications of excilampsApplications of excilamps

300x103

200

100

0

Irrad

ianc

e (u

.a.)

700600500400300200Wavelength (nm)

Xenon/Chlorine excilamp

Xenon/Chlorine excilamp spectrum

Industrial:- Photochemistry

Environment:- Water Treatment- Sterilization

Health:- skin disease treatment

UVB radiation especially suited for treatment of psoriasis and vitiligo.

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Model DescriptionModel Description

Fluid model:

Plasma out of equilibrium Boltzmann equation

Drift-diffusion equations:

⎪⎩

⎪⎨⎧

±∇−=Γ

=Γ∇+∂∂

EnnD

Stn

rvr

rr

μ

.

⎪⎪⎪⎪⎪

⎩

⎪⎪⎪⎪⎪

⎨

⎧

=∇−∇−∇+∂∂

=∇+∇−∇+∂∂

−=∇−∇

........

.......

).(

).(

)().(

iiiiii

eeeeee

ei

SVnnDtn

SVnnDtn

nneV

rrr

rrr

rr

μ

μ

ε

PDE system to solve:

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*metXe

*resXe

*excXe

+Xe+2Xe

)0(*2

+uXe

)(1*2

+ΣuXe

)(3*2

+ΣuXe

Xe

−e

−e

−e

−e

Ene

rgy

(eV

)

0

8,45

12,13

8,32

Xe2

−e

Xe

XeXe

−e

Xe

Xe

Xe2

Xe2

CollisionsRadiative transitions

152n

m

172n

m

147n

m

Model DescriptionModel Description

Chosen kinetics scheme:

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Boundary conditions:1 - Coupling of volume densities and surface densities through the Weak Boundary Application mode

isesrecsesdesesadsese nnKnKnK

dtdn

−−=

siesrecsesdesesadsene nnKnKnKu +−=Γrr

.For electrons

1 – Boundary Conditions for the Electrostatic Potential

)10502sin(5000)2( ;0)1( 3 telectrodeVelectrodeV ×== π

dtAtIelectrodeVelectrodeV

t

∫=∇=0

)()2(;0)1(v

ε

Electric field discontinuity is taken into account at the charged dielecticboundaries

Voltage Source

Current Source

Model DescriptionModel Description

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Model DescriptionModel Description

0.0020.006

0.008

Metallic electrodes

Dielectriclayers

(dimensions in m)

Discharge gap

to the ground

to the voltage generator

Considered geometry:

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Results obtainedResults obtained

2.10-3

46

x1019

3Σu+ excimer

density (m-3)

position (m)6.10-3

ωt (rad)

0

2π4π

2

3Σu+ excimer

density (m-3)

1

2.10-3

34x1018

electrondensity (m-3)

position (m)6.10-3

ωt (rad)

0

2π

4π

electrondensity (m-3)

0 0.5 1 1.5 2 2.5 3 3.5 4

x 10-5

-1.5

-1

-0.5

0

0.5

1

1.5x 10

4

Time (s)

Vol

tage

s an

d C

urre

nt (

units

in le

gend

)

Comparison between the electrical and the PDE model results in sine wave form at

50kHz Legend:

Applied voltage (V)Voltage drop in the whole gas gap according to the PDE model (V)Total current according to the PDE model(x106A)

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50 100 150 200 250 300 3500.45

0.5

0.55

0.6

Fréquence (kHz)

η172

Efficiency of the excilamp supplied with a sine waveform voltage source.

Results obtainedResults obtained

Frequency (kHz)

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10 30 40 50 800.55

0.6

0.65

0.7

0.75

0.8

Rapport cyclique α (%)

η172

Voltage (V)

-8kV

8kV

1μs 1μs

1μs 1μs

20μs

1τ

1τ

0τ

0τ

=τ

ττα 12

=

Time (μs)

Voltage (V)

-8kV

8kV

1μs 1μs

1μs 1μs

20μs

1τ

1τ

0τ

0τ

=τ

ττα 12

=

Time (μs)

Duty ratio (%)

Results obtainedResults obtained

Efficiency of the excilamp supplied with a pulsed waveform voltage source.

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0 0.5 1 1.5 2 2.5

x 10-5

-1

-0.5

0

0.5

1

1.5x 10

4

Tim e (s ec)

V

Ls=1e-5 H

Ls=5e-5 H

Ls=1e-4 HLs=5e-4 H

Vs

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x 10-3

10

20

30

40

50

60

70

80

90

100

Ls

Pe

rce

nta

ge E

ffic

ien

cyResults obtainedResults obtained

Electrical scheme

Effect of Ls on DBD Efficiency

DBD Voltage under different parasitic inductances

“Simulation of Dielectric Barrier Discharge Lamp Coupled to the External Electrical Circuit” - A. El-Deib, F.P. Dawson, S. Bhosle, D. Buso and G. Zissis – COMSOL Conference 2008 - Boston

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"Design of a Current Converter for the Study of the UV Emission in DBD Excilamps" - R. Díez, H.Piquet, S. Bhosle, J.M. Blaquière, N. Roux - ISIE 2008 IEEE International Symposium on IndustrialElectronics, 30 june-2 july 2008 - Cambridge (England)

Design of a dedicated powerconverter

Results obtainedResults obtained

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ConclusionConclusion

- A PDE model was used to compute the parameters of an operating excilamp- This model was implemented in COMSOL Multiphysics and could be successfully solved in 1D - time dependant- Thanks to COMSOL platform, the model can easily be shared with researchers from abroad of from different backgrounds- The obtained results help in the understanding of the mechanisms involved in the development of the discharge- They led to the design of new power converter topologies, specially dedicated to excilamps