CEAGrenoble DSMINACSBT SHF workshop, Grenoble 892008

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PHYSICAL MODELING OF THE BOILING CRISIS THEORY
AND EXPERIMENT V. Nikolayev, D. Chatain, D.
Beysens Team of Supercritical Fluids for
Environment, Materials and Space, ESPCI/PMMH
(Paris), SBT/INAC/CEA (Grenoble), France
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Boiling crisis (DNB) transition from nucleate
to film boiling
Nucleate boiling (separate vapor bubbles)

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Zubers (1958) mechanism of the boiling crisis
instability of the vapor stems
Zuber-Kutateladze formula qCHF H? g (?L -?V
)?V 21/4
H latent heat ? surface tension g
gravitation ?L (?V) liquid (vapor) density
But vapor stems observed rarely while the
boiling crisis is ubiquitous! Boiling crisis
triggering mechanism? (Triggering mechanism ? CHF
value )
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Boling crisis mechanism at which scale?

• System?
• Macroscopic flow structure?
• Multi-bubble coalescence of the bubbles sitting
  at the heater?
• Single bubble growth and departure?
• Triple contact line micro-region?

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BC mechanism recent experimental observations
(pool boiling, low pressures)

• Teophanous et al. (2002)
• Kandlikar et al. (2002)
• Chung et al. (2003)
• Nishio et al. (2004) ?
• Importance of dry spot growth on the heater
• Observations through the transparent heater

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BC mechanism single bubble spreading due to
vapor recoil

• Vapor recoil force (per unit area) Pr? 2 (?V-1
  - ?L-1 )
• evaporation rate (mass per time and area)
  qL/H
• H latent heat qL heat flux consumed by
  evaporation

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Numerical simulation by BEM
Water at 10 MPa ? Tsat311C dmin10-3 R0
R050µm
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Actual and apparent contact angles. Vapor recoil
adhesion.
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CHF determination
1st regime Vapor film nucleation bubble growth
and spreading
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Vapor recoil vs Zubers mechanism
Vapor recoil surface tension
, where
qCHF H? g (?L -?V )?V 21/4
Zuber-Kutateladze

• Equivalent at low pressures (?L ltlt?V )!
• qCHF g1/4

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CHF vs gravity (Water at 10 MPa)
g1/4
The curve is not exactly g1/4 ? simulations are
necessary
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Vapor recoil vs Zubers mechanism at nearly
critical pressure
Vapor recoil mechanism qCHF (pc-p)1.14 Zubers
model qCHF (pc-p)0.72
But surface tension?0, bubbles are inexistent in
Earth gravity ? reduced gravity is necessary
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Experiment in µg with SF6
(Mir space station, 1996-1998)
vapor bubble
Bubble spreading under vapor recoil
influence Actual contact angle is zero!
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Gravity compensation by magnetic forces with H2
(CEA-Grenoble 2006)
Endoscope For observation
Vacuum vessel For the cell
Coil
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Experimental cell
Sapphire Windows
8 mm
Heaters
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CHF observation
heating
observation direction
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Boiling curves

• Each point a stationary state

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CHF at nearly critical pressure
(pc-p)/pc
Vapor recoil mechanism qCHF (pc-p)1.14 Zubers
model qCHF (pc-p)0.72
Nikolayev V. S. et al. Phys. Rev. Lett.
(2006). Publicity Physics Today (2007) APS
News (2007).
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Future space experiments DECLIC
Dispositif pour lEtude de la Croissance et des
LIquides Critiques (Facility for the study of
crystal growth and critical fluids) CNES
(17M)NASA, International Space Station (ISS)
2009
DECLIC on the test banc
Integration of DECLIC into ISS rack
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Future magnetic levitation experiments
OLGA Oxygen Low Gravity Apparatus
Superconductive coil D650mm d330mm H555mm
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Conclusions

• The vapor recoil model can explain
  self-consistently the triggering of the boiling
  crisis
• Existing experiments confirm the model both
  qualitatively and quantitatively, however
  further experiments are needed (e.g. to
  quantify the gravity influence)
• At least two more series of experiments
  (magnetic levitation of O2 and SF6 in DECLIC
  facility at ISS) are foreseen
• Simulations can predict the CHF value for
  different parameters
• - contact angle
• - material parameters and geometry
• - gravity level
• Account of hydrodynamics in simulations is
  necessary
• Joint project ALICE with CEA/SSTH, IMFT, LMS
  (2008-)

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Acknowledgements

• CNES
• Air Liquide

Thank you for your attention!
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