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Computational plasma physics: HID modeling with Plasimo

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1. Introduction (3): vertical burning MH lamps. Goal: ... Cermet. sealing glass. ceramic vessel. electrode. salt pool. Nb wire. Plasma arc: global properties ... – PowerPoint PPT presentation

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Title: Computational plasma physics: HID modeling with Plasimo


1
Computational plasma physicsHID modeling with
Plasimo
  • D.A. Benoy
  • Philips Lighting, CDL,
  • MDHT

2
Contents
  • Introduction
  • Modelling HID burners
  • HID plasma modelling
  • Why Plasimo
  • Plasimo extensions
  • Results computational analysis
  • Conclusions

3
Introduction (1)
  • Discharges for lighting
  • Low pressure
  • Hg fluorescent (TL)
  • Na Sox
  • High pressure
  • Hg UHP (radiation source)
  • Hg CDM, MH, (buffer gas)

4
1. Introduction (3) vertical burning MH lamps
top
Observation axial segregation gt efficiency
loss (vert.) gt color depends on burning
position
Na Hg radiation
Goal understanding, optimizing effects of
de-mixing.
Na RE Hg radiation
bottom
5
2. Modeling HID (1) Global energy balance
Pin
PdischargePin-Pelect
Pelect
Prad
Pcond/conv
PUV
Pbulb
Pvis rad
PIR
Multi-component discharge
Electrode modeling
Burner bulk discharge
6
2. Modeling HID (2)
Focus on burner during lamp operation Thermal
modeling
With commercial package e.g. ANSYS (finite
elements) Emphasis on geometry details.
Total radiation Empiric expression
Different colors represent different materials
7
2. Modeling HID (3)
  • Thermo-mechanical modeling
  • Study mechanical behaviour (stresses) of CDM
    (PCA) burners as result of plasma heating Global
    plasma modelling is included for calculating
    thermal wall load.
  • Optimise burner design.
  • Detailed properties of discharge not needed.
  • Detailed description of burner geometry, and
    burner material properties needed.
  • Use of commercial packages ANSYS

8
2. Modeling HID (4)
9
3. HID plasma modeling (1)
  • Discharge modelling
  • What?
  • Study physical processes in the plasma of the
    burner (radiation, lamp voltage, local
    composition (de-mixing), heat transfer, ).
  • Optimise design rules for gas discharge lamps
    w.r.t. light-technical properties (Colour
    Rendering Index properties of spectrum,
    efficacy, colour temperature)
  • Detailed properties of discharge are needed.
  • High pressures discharge ? continuum approach

10
3. HID plasma modeling (2)
In this lecture focus on modeling detailed
properties of discharge.
  • Plasmas in MH discharge lamps are complex
    systems
  • Which physical processes?
  • Plasma as a light source ? solve energy balance,
  • Light properties are determined by salt
    additives ? solve chemical, and transport
    balance of minority species (i.e. multi-component
    plasma),
  • For vertical burning position gravitation
    influences local chemical composition by means of
    natural convection ? solve flow-field.
  • ? Understanding, optimizing effects of de-mixing
    of minority species (MH)

11
3. HID plasma modeling (3)
  • Physical model assumptions for mass, and energy
    transport balances
  • Local chemical equilibrium (LCE) for species
    composition in liquid (salt-pool) and gas phase,
    i.e. determination of local partial pressures of
    radiating species.
  • Transport of minority species by diffusion, and
    convection.
  • Radiation transport
  • Absorption, and self-absorption,
  • Include broadening mechanisms.
  • Ohms law for electric field, and current density
    (electrode end effects).
  • Model constraints
  • Transport coefficients calculated from plasma
    composition,
  • Number of fit parameters (in radiation, and
    transport coefficients) as small as possible.

12
3. HID plasma modeling (4)
  • Plasma simulation model requirements
  • Calculation chemical composition,
  • Transport of minority species by diffusion, and
    convection
  • Not limited by species
  • Not limited by diffusion - convection mechanisms
  • Radiation transport,
  • Flow-field solver,
  • Thermal k, electric s conductivity, viscosity,
    and diffusion coefficients function of plasma
    state, and composition,
  • 2-dimensional E-field.

13
3. Plasma balance equations
Bulk, ambipolar, reactive
Mass balance
Elemental flux
Elemental diffusion
Species flux
Stoichiometric coefficient
Vertical burning position
Momentum balance
Energy balance
Electric field
Ohmic dissipation
Radiation term
14
4. Which simulation package?
  • Flaws of commercial packages
  • Non-local radiation transport,
  • Limited number of species,
  • Limited number of diffusion mechanisms,
  • Limited functionality of user sub-routines (no
    source code)
  • PLASIMO does not have these short-comings
  • Flaw of PLASIMO
  • Limited freedom in modeling electrode geometry.
    For detailed modeling of discharge not serious
    problem.
  • Additional issues
  • Flexibility w.r.t. minor extensions, and
    modifications,
  • Nearby support, including implementation major
    extensions,
  • Cheap

15
5. Plasimo extensions (1)
  • Electric potential solver for finite electrodes
  • div J 0,, J ?E, E -??
  • -???? 0
  • new EM plug-in needed. Make use of standard ?
    equation.

16
1. Add new constructor
class grdEXP plPoissonVariable public
plPhiVariable class ConstTerm public
plDoublePhiTermContribution
public void Update()
plGridVarltREALgt m_field
ConstTerm( plModelRegion reg, REAL val )
public plPoissonVariable(
plModelRegion reg, const stdstring Aname,
const plNode node )
plPoissonVariable( plModelRegion reg,
const stdstring Aname,
const plNode node,
plRememberingGridVarltREALgt sig )
2. Add new class
class plEME2dCurrentData public plBaseEMData
private REAL m_power
public plEME2dCurrentData( plModelRegion
reg, const plNode node ) virtual void
CalculateFields(REAL acc ) REAL
Accuracy() const return m_potential.Accuracy()
protected plPoissonVariable
m_potential
17
3. Implement constructor of new class
plEME2dCurrentDataplEME2dCurrentData(
plModelRegion reg, const plNode emnode )
plBaseEMData( reg, emnode ),
m_potential( reg, "Potential", emnode"EMPotential
FromCurrent", sig )
4. Instruct how to calculate fields
void plEME2dCurrentDataCalculateFields( REAL
acc ) m_potential.Update( acc ) //
calculate the electric fields gradient(
m_potential.tbcimat(),
m_Eimposed1.tbcimat(), m_Eimposed2.tbcimat(),
m_potential.fdgrid() )
5. Export plug-in
class plEME2dCurrent public plBaseEMProxyltplEME2d
CurrentDatagt REGISTER_PROVIDER( plBaseEM,
plEME2dCurrent, "E2dCurrent")
18
5. Plasimo extensions (2) Composition
  • PLASIMO has own solver for calculation of
    composition
  • E.g. 8 species Hg (buffer), Hg, Na, Na, I, I,
    NaI, e
  • 3x ionisation ( X e ? X 2e)
  • 1x dissociation (Na I ? NaI)
  • Charge neutrality
  • ?Pelemental Pbulk
  • ??
  • 2x elemental diffusion balance

19
5. Plasimo extensions (2) Composition
  • 2. At CDL and PFA a chemical database is already
    available. ?
  • Plasimo needs to call external library for
    calculating species partial pressures. CHEMAPP
    (Gibbs minimizer, commercial package ? only DLL
    available)
  • Windows version of Plasimo required.
  • New composition plug-in.

Hg (buffer), elements Na, I, Ce, e CHEMAPP
called for each grid point ?? 2x elemental
diffusion balance
20
5. Plasimo extensions (2) chemapp initialization
Initialization Geometry, grid
Plasma parameters
Buffer gas pressure (for Hg based on dose and,
effective temp. Cold spot temperature Salt doses,
CHEMAPP returns initial values for elemental
pressures. These values must be transferred to
Elemental function node ? Install again (input
data is constant)
CHEMAPP
Cold spot elemental partial pressures Apply to
whole plasma Local temperature (init distribution)
Transport coefficients
User fit models, or Different interaction
potentials
Start main loop
21
5. Plasimo extensions (3)
  • Implementing various line broadening mechanisms
    in radiation transfer module (ray tracing
    method) data from CDL.
  • Pressure
  • Stark
  • Doppler

22
6. Results 2D Electric potential
Electrode distance (Z) 24mm Burner radius
(R) 6mm Electrode radius 0.5mm DF 2V s constan
t NZ 40 NR 40
Electrode
Large E-field ? Large DT ? Source of difficulties
23
6. Results2D Electric potential, and
temperature (1)
Electrode distance (Z) 32mm Burner radius
(R) 4mm Electrode radius 0.5mm s F(T) (Fit
from PFA data Hg (buf) Na I) Total
power 70W Electrode temperature 2900K NZ 120 NR
40 Regular grid
selectrode s(lte) selectrode s(n-lte) gt s(lte)
Profiles not realistic
24
6. Results estimation thermal gradient at
electrode
First grid point regular grid at 1.6x10-4m Is too
large. If equidistant grid ? 1000 axial
points needed!
? Axial grid transform (2-point stretch)
25
6. Grid transformation
Computational grid equi-distant control volumes
Electrode
Physical grid transformed control volumes
Fine mesh at tip required, First gridline at 10mm
26
6. 2D Electric potential, and temperature (2)
Electrode distance (Z) 32mm Burner radius
(R) 4mm Electrode radius 0.5mm s F(T) Total
power 70W NZ 120 NR 40 Transformed grid
selectrode s(lte) selectrode gt s(lte)
27
Heat flow analysis at electrode tip
28
  • Estimated electrode heat loss
  • Heat flux at middle of electrode
  • qkDT/Dx
  • q 0.091000/10-5 0.09108W/m2 ? Total
    electrode loss 7.8W
  • q 0.141900/10-5 0.27108 23.5W
  • q 2.905700/1.610-4 1.03108 66W
  • Is 8.5larger!
  • Much higher heat lost through electrode
    unrealistic
  • Power input 70W
  • Rule of thumb ? 10 15 electrode losses.

Values for s(n-lte), Telectrode? Near electrode
(e-source) there is deviation from
equilibrium. Plasma model equilibrium ?
s(n-lte), and Tinput are input data. Coupling
with electrode model for self-consistent
calculation of s(n-lte), and Tinput .
29
Checking E, and current density
3-rd axial gridpoint Radial integrated Jx is
obviously overestimated. What is the reason?
(physical, or numerical background?)
30
No 2-nd order polynomial curve fitting Ez(boundary
, not electrode) 0.
31
6. Buffergas calculation (1) E, T, flow field, Hg
  • Influence of buffer gas pressure
  • on flow field (maximum velocity)
  • Temperature distribution
  • Convergence

32
6. Buffergas calculation (2) Flow field
Gravity
Only buffer gas (10 bar)
Only buffer gas (40 bar)
Only buffer gas (80 bar)
33
6. Buffer gas calculation (3) temperature
Gravity
Only buffer gas (10 bar)
Only buffer gas (40 bar)
Only buffer gas (80 bar)
34
6. Buffer gas calculation (4) temperature
35
6. Convergence buffer gas calculations
Only buffer gas (40 bar)
Only buffer gas (80 bar)
36
6. Results (5)
 
 
pi
Axial velocity saturates?
Na-I-Hg discharge ID 14 mm IL 32
mm Parabolic T-profile Hard-spheres
diffusion 1D-Electric field (large radius
electrode)
ID 8 mm IL 32 mm Calculated
T-profile 2D-Electric field (small radius
electrode)
37
6. Results (4)
Buffer gas (10 bar) Na, and I additive (10mbar)
Gravity
38
6. Results (4)
Only buffer gas (10 bar)
Buffer gas (10 bar) Na minority (10mbar)
39
7. Conclusion, and future work
  • Plasimo is powerful, and flexible tool for
    optimizing discharges used for lamps (calculating
    plasma physical, and radiation properties ? light
    properties)
  • 2-D electric field has significant influence on
    flow field,
  • Flexible
  • can be linked with third party (commercial)
    libraries,
  • Small modifications can be implemented at CDL,
  • Large modifications implemented by TUE.

Current and future work
  • Electrode boundary conditions (F),
  • Implementation radiation transport for rare-earth
    radiators (C, solution algorithm is free,
    radiation data is not free) ,
  • Calculation wall loads (F)

40
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