november 20, 2002 a. r. raffray, et al., thin liquid wall behavior under ife cyclic operation 1 thin...

November 20, 2002 A. R. Raffray, et al., Thin Liquid Wall Behavior under IFE Cyclic Operation 1

Thin Liquid Wall Behavior under IFE Cyclic Operation

A. R. Raffray1, S. I. Abdel-Khalik2, D. Haynes3, F. Najmabadi4, J. P. Sharpe5 and the ARIES Team

1Mechanical and Aerospace Engineering Department and Center for Energy Research, University of California, San Diego, EBU-II, Room 460, La Jolla, CA 92093-0417

2School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-04053University of Wisconsin, Fusion Technology Institute, 1500 Engineering Drive, Madison, WI 53706-1687

4Electrical and Computer Engineering Department and Center for Energy Research, University of California, San Diego, EBU-II, Room 460, La Jolla, CA 92093-0417

5Fusion Safety Program, EROB E-3 MS 3860, INEEL, Idaho Falls, Idaho 83415-3860

15th Topical Meeting on the Technology of Fusion Energy

Washington, D.C.November 20, 2002


Outline• IFE chamber operating conditions

• Thin Liquid Wall Configuration– Attractiveness and key issues

• Film Establishment and Coverage – Wetted wall

– Forced film flow

• Film Condensation

• Aerosol formation and behavior – Aerosol source term (including explosive boiling estimate)

– Aerosol formation and transport analysis

– Design windows (including driver and target constraints)

• Concluding Remarks


IFE Operating Conditions

• Cyclic with repetition rate of ~1-10 Hz • Target injection (direct drive or indirect drive)

• Driver firing (laser or heavy ion beam)

• Microexplosion

• Large fluxes of photons, neutrons, fast ions, debris ions toward the wall

- possible attenuation by chamber gas

Target micro-explosion

Chamber wall

X-rays Fast & debris ions Neutrons

Example of Direct-Drive Target (NRL) (preferred option for coupling with laser driver)

DT Vapor0.3 mg/cc

DT Fuel

CH Foam + DT

1 m CH +300 Å Au

.195 cm

.150 cm

.169 cm

CH foam = 20 mg/cc

Example of Indirect-Drive Target (LLNL/LBLL) (preferred option for coupling with heavy ion beam driver)


Energy Partitioning and Photon Spectra for Example Direct Drive and Indirect Drive Targets

NRL DirectDrive Target(MJ)

HI IndirectDrive Target(MJ)

X-rays 2.14 (1%) 115 (25%)

Neutrons 109 (71%) 316 (69%)

Gammas 0.005 (0.003%) 0.36 (0.1%)

Burn ProductFast Ions

18.1 (12%) 8.43 (2%)

Debris IonsKinetic Energy

24.9 (16%) 18.1 (4%)

ResidualThermal Energy

0.013 0.57

Total 154 458

Energy Partitions for Example Direct Drive and Indirect Drive Targets

Photon Spectra for Example Direct Drive and Indirect Drive Targets

• Much higher X-ray energy for indirect drive target case (but with softer spectrum)

• Basis for example wetted wall analysis presented here

(More details on target spectra available on ARIES Web site: http://aries.ucsd.edu/ARIES/)

(25%)

(1%)


IFE Thin Liquid Wall Configuration

Key processes: Thin film dynamics Condensation Aerosol formation and behavior These are assessed here with Pb

and flibe as example fluids

Injection from the back

Condensation

Ablation

Pg

Tg

Film flow

Photons

Ions

In-flight condensation

• Advantages of decoupling functions:– Armor function to accommodate

X-ray and ion threat spectra provided by renewable liquid film for longer lifetime

– Structural and energy recovery functions provided by solid blanket at the back for high efficiency

• Major issues:– Film establishment and coverage

• Film dynamics

• Injection method

• Geometry effects

• Recondensation

– Ablated material and chamber clearing requirements

• Ablation processes

• Film condensation

• Aerosol formation and behavior

• Driver and target requirements


Film Dynamics

• Two Injection Methods Considered

- Radial injection through a porous first wall ( “wetted wall” design)

- Forced flow of a thin liquid film tangential to a solid first wall (“forced film” design)

• Critical Questions Include:(1) Can a stable liquid film be maintained on the upper section of the chamber?

(2) Can the film be re-established over the entire cavity surface prior to the next target explosion?

(3) Can a minimum film thickness be maintained to prevent dry patch formation and

provide adequate protection during the next target explosion.

• These Questions are Being Addressed through Complementary Modeling and Experimental Investigations- Example results illustrated here


Example of Wetted Wall Investigation

• Modeling simulation of 3-D evolution of liquid film surface based on:

- Liquid injection velocity through porous wall

- Surface disturbance amplitude, configuration and mode number

- Surface inclination angle

- Liquid properties

- Effect of film evaporation and/or condensation

• Results used to develop “generalized charts,” showing effects of these

variables on:- Frequency of liquid drop formation and

detachment,

- Size of detached droplets

- Minimum film thickness prior to droplet detachment

• Example results for 700 K Pb with initial thickness of 1.0 mm and injection velocity of 1.0 mm/s

• Random initial perturbation with maximum amplitude of 1.0 mm applied beginning of the transient

• In this case, droplet detachment occurs ~0.38 s after initial perturbation

t = 0.38 st = 0.37 s

t = 0.32 s t = 0.35 s

• Poster presented during Tue. afternoon session (1.27)


Examples of Forced Film Investigation

• Film detachment most likely to occur on downward facing surfaces in upper part of chamber

- Could interfere with beam propagation and/or target injection

• Experimental study to determine film detachment distance as a function of:

- Wetting and non-wetting surfaces

- Initial film thickness (1.0 to 2.0 mm)

- Film injection velocity (1.9 to 11.0 m/s)

- Inclination angle (0º to 45º) • Poster presented during Tue. afternoon session (1.31)

0

200

400

600

800

1000

1200

1400

1600

0 20 40 60 80 100 120 140Fr

Film detachment distance vs. Froude number for horizontal downward-facing surfaces

wetting surface

Non-wetting surface

1.5 mm

2.0 mm

1.0 mmFilm thickness:

Flow of 1.5 mm thick film with a 5.0 m/s velocity around 25.4 mm dia., 2.4 mm high cylindrical “port.”

• Experimental study of behavior of thin liquid films flowing around cylindrical obstacles,

typical of beam and target injection ports

- Such obstacles will pose significant challenge to designers

- Efforts underway to examine behavior of thin films flowing past "streamlined" obstacles.


Film Condensation Rate is Fast

• Characteristic time to clear chamber, tchar, based on condensation rates and Pb inventory for given conditions

• For higher Pvap, tchar is independent of Pvap

- Probably more limited by heat transfer effectiveness

• As Pvap decreases and approaches Psat, tchar increases substantially

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

1x100 1x101 1x102 1x103 1x104 3x104

Vapor Pressure (Pa)

Pb:Film temperature = 1000KFilm Psat = 1.1 Pa

Vapor velocity = 0

Vapor Temp. (K)

1200

10,000

5000

2000

ƒƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ

æ

ææ æ æ æ æ æ æ æ æ

ø

ø ø ø ø ø ø ø ø ø ø

”

” ” ” ” ” ” ” ” ” ”

0

0.02

0.04

0.06

0.08

0.1

0.12

1x100 1x101 1x102 1x103 1x104 1x105 1x106

Vapor pressure (Pa)

ƒ

æ

ø

”

Pb film temperature = 1000KFilm Psat = 1.1 Pa

Vapor velocity = 0Chamber radius = 5 m

Vapor Temp.

10,000 K

5000 K

2000 K

1200 K • Typically, IFE rep rate ~ 1–10

• Time between shots ~ 0.1–1 s

• Pvap prior to next shot ~(1-10)Psat

• Can be controlled by setting Tfilm

• Of more concern is aerosol generation (in-flight condensation) and behavior

Example Analysis of Pb Vapor Film Condensation in a 10-m Diameter Chamber


Processes Leading to Vapor/Liquid Ejection Following High Energy Deposition Over Short Time Scale

Energy Deposition &

Transient Heat Transport

Induced Thermal- Spikes

Mechanical Response

Phase Transitions

•Stresses and Strains and Hydrodynamic Motion•Fractures and Spall

• Surface Vaporization•Heterogeneous Nucleation•Homogeneous Nucleation (Phase Explosion)

Material Removal Processes

Expansion, Cooling and

Condensation

Surface Vaporization

Phase Explosion Liquid/Vapor

Mixture

Spall Fractures

Liquid

FilmX-Rays

Fast Ions

Slow Ions

Impulse

Impulse

y

x

z


High Photon Heating Rate Could Lead to Explosive Boiling

Photon-like heating rate

Ion-like heating rate

• Effect of free surface vaporization is reduced for very high for heating rate (photon-like)

• Vaporization into heterogeneous nuclei is also very low for high heating rate

From K. Song and X. Xu, Applied Surface Science 127-129 (1998) 111-116

• Rapid boiling involving homogeneous nucleation leads to superheating to a metastable liquid state

• The metastable liquid has an excess free energy, so it decomposes explosively into liquid and vapor phases.

- As T/Ttc increases past 0.9, Becker-Döhring theory of nucleation

indicate an avalanche-like and explosive growth of nucleation rate (by 20-30 orders of magnitude)


Photon Energy Deposition Density Profile in Flibe Film and Explosive Boiling Region

1x107

1x108

1x109

1x1010

1x1011

1x1012

0 5 10 15

Penetration depth (micron)

Cohesion energy (total evaporation energy)

2.5

Evap.region

10.4

2-phase region

Sensible energy (energy to reach saturation)

Sensible energy based on uniform vapor pressure following photon passage in chamber and including evaporated Flibe from film

0.9 Tcritical

4.1

Explo.boil. region

Bounding estimates of aerosol source term:(1)Upper bound: the whole 2-phase region; (2)Lower bound: explosive boiling region

• Posters on flibe properties presented during Tue.& Wed. afternoon sessions (1.38 & 2.36)


• Spherical chamber with a radius of 6.5 m

• Surrounded by liquid Pb wall

• Spectra from 458 MJ Indirect Drive Target

• Explosive boiling source term (2.5m, lower bound)0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5

Radial Position (m)

Region 1Region 2

Region 3Region 4

Analysis of Aerosol Formation and Behavior

Region 1

• From the analysis, aerosol formation could be a key issue and need to be further addressed

• Driver and target constraint also need to be more accurately defined

10 5

10 7

10 9

10 11

10 13

10 15

0.1 1 10

aero_I_data

100 µs500 µs1 ms5 ms10 ms100 ms250 ms

Number Concentration (#/m

3)

Particle Diameter (µm)

• Appreciable # and size of aerosol particles present after 0.25 s

• ~107-109 droplets/m3 with sizes of 0.05-5 m in Region 1

• Preliminary estimate of constraints:

- Target tracking based on 90%beam propagation

- Heavy ion driver based on stripping with integrated

line density of 1 mtorr for neutralized ballistic transport


• Spherical chamber with a radius of 6.5 m

• Spectra from 458 MJ Indirect Drive Target

• Explosive boiling source term (5.5 m)0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5

Radial Position (m)

Region 1Region 2

Region 3Region 4

Analysis of Aerosol Formation and Behavior for Flibe

• Aerosol size and # after 0.25 s

- 107-109 droplets/m3 with sizes of 0.3-3 m

- Exceeds driver limit

• Again, from this analysis, aerosol formation could be a key issue

• Needs to be addressed by future effort

• Oral presentation during Thu. morning session

Region 1

10 5

10 7

10 9

10 11

10 13

10 15

0.1 1 10

aero_I_data

100 µs500 µs1 ms5 ms10 ms100 ms250 ms

Number Concentration (#/m

3)

Particle Diameter (µm)

Target tracking constraint

Neutralized ballistic transport: stripping constraint


Concluding Remarks

• Wetted walls provide possibility of high efficiency and renewable armor

• Key issues are film establishment and chamber conditions prior to next shot

• Experimental and modeling effort under way to provide generalized charts for designing film injection system:- Wetted wall (droplet detachment, minimum film thickness…)

- Forced film flow (film detachment, beam port obstacles...)

• High energy deposition rate of X-rays would lead to explosive boiling- Provide bounding estimates for aerosol source term

• Aerosol modeling analysis indicate substantial # and size of droplets prior to next shot for both Pb and FLiBe- Preliminary estimates of constraints for indirect-drive target and heavy ion driver

- Marginal design window (if any)

• Future effort:- Completing generalized charts on film dynamics

- Better understanding aerosol source term and behavior

- Confirmation of target and driver constraints


Other ARIES-IFE Related Presentations at 15th TOFE • S. Shin, S. I. Abdel-Khalik, D. Juric and M. Yoda, ”Effects of surface evaporation and

condensation on the dynamics of thin liquid films for the porous wetted wall protection scheme in IFE reactors,” Tue. afternoon poster session, 1.27

• J. K. Anderson, M. Yoda, S. I. Abdel-Khalik and D. L. Sadowski, “Experimental studies of high-speed liquid films on downward-facing surfaces,” Tue. afternoon poster session, 1.31

• M. Zaghloul, D. K. Sze and R. Raffray, “Thermo-physical properties and equilibrium vapor-composition of lithium fluoride-beryllium fluoride (LiF/BeF2) molten salt,” Tue.

afternoon poster session, 1.38

• L. El-Guebaly, P. Wilson, D. Henderson, L. Waganer, R. Raffray and the ARIES Team, “Radiological issues for thin liquid walls of ARIES-IFE study, Tue. afternoon poster session,

1.51

• J. P. Sharpe, B. J. Merrill and D. A. Petti, “Aerosol production in IFE chamber systems,” Thu. Morning oral session

• L. El-Guebaly, P. Wilson, D. Henderson, A. Varuttamaseni and the ARIES Team, “Feasibility of target material recycling as waste management alternative, “ Thu. Morning

oral session

• M. Zaghloul, “Ionization equilibrium and thermodynamic properties of high-temperature FLiBe vapor in wide range of densities,” Wed. afternoon poster session, 2.36

november 20, 2002 a. r. raffray, et al., thin liquid wall behavior under ife cyclic operation 1 thin...

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