A1260253826hJcFi

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On the Enhancement of the Critical Heat Flux in
Water-Based Nanofluids for Applications in
Nuclear Systems
Presented by Prof. Jacopo Buongiorno Co-authors
Sung Joong Kim, In Cheol Bang, Lin-wen Hu
Nuclear Science and Engineering
Department Massachusetts Institute of Technology
Workshop on Modeling and Measurements of
Two-Phase Flows and Heat Transfer in Nuclear Fuel
Assemblies KTH, Stockholm, October 10-11, 2006
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Outline

• Intro to nanofluids
• MIT program research highlights
• single-phase heat transfer
• boiling heat transfer
• Promising nuclear applications
• Conclusions

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Nanofluids

• Nanofluids are engineered colloids base fluid
  (water, organic liquid) nanoparticles
• Nanoparticle size 1-100 nm
• Nanoparticle materials Al2O3, ZrO2, SiO2, CuO,
  Fe3O4, Au, Cu, C (diamond, PyC, fullerene) etc.
• Previous studies suggest significant enhancement
  of
• Thermal conductivity (40)
• Single-phase convective
• heat transfer (40)
• Critical Heat Flux (100)

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Nanofluid Research Program at MIT

• Objectives
• Measure and understand key transport phenomena in
  nanofluids
• Evaluate nanofluids applicability to nuclear
  systems
• Other applications include processor cooling, air
  conditioning, automotive cooling
• Faculty (2), staff (3), students (8), post-doc
  (1) involved
• Sponsors include INL, AREVA, NRC and NRL
• Collaborations with MIT MechE, MIT ChemE, UFL,
  U-Leeds, POLIMI, Olin College, RPI

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Research Highlights
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Nanofluid Thermal Conductivity
Measured thermal conductivity of gt20 nanofluids
with transient hot wire technique
No abnormal thermal conductivity enhancement
observed
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Nanofluid Convective Heat Transfer
Measured heat transfer coefficient and pressure
drop in flow loop

• Nanofluids seem to follow traditional heat
  transfer behavior
• No heat transfer enhancement detected so far

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Nanofluid Critical Heat Flux
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Why Does CHF Increase?

• Thermophysical properties do not change
  significantly at low nanoparticle concentration

Nanoparticles DI water Al2O3 Al2O3 Al2O3 ZrO2 ZrO2 ZrO2 SiO2 SiO2 SiO2
Concentration (v) 0.0 0.1 0.01 0.001 0.1 0.01 0.001 0.1 0.01 0.001
Particle size (nm) 0.0 132.6 133.6 113.7 136.5 496.1 226.6 21.5 N/A N/A
Boiling point (oC) 1.1oC error 100.6 100.8 100.8 N/A 100.1 100.4 N/A 100.9 101.0 N/A
Surface tension (mN/m) 1 error 72.5 74.8 73.4 73.2 73.7 73.4 73.4 72.4 72.9 73.0
Kinematic viscosity (cSt) 1 error 0.92 0.93 0.93 0.94 0.93 0.93 0.93 0.92 0.93 0.93
Thermal conductivity (W/moK) 1 error 0.59 0.59 0.59 0.58 0.59 0.59 0.59 0.59 0.59 0.59
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Why Does CHF Increase? (2)

• Heater surface does change upon nanofluid
  boiling!!

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Why Does CHF Increase? (3)
Measurements of nanoparticle deposition on heated
surface during boiling
Plate Type Heater SS316
SEM Clean SS316 Surface
EDS Clean SS316 Surface
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Why Does CHF Increase? (4)
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Why Does CHF Increase? (5)
Surface wettability increases dramatically
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Why Does CHF Increase? (6)

• CHF theories
• Hydrodynamic Theory
• Macrolayer Dryout Theory
• Hot/Dry Spot Theory
• Bubble Interaction Theory
• - 1 predicts no effect of wettability on CHF
• - 2, 3 and 4 predict CHF enhancement if
  wettability increases

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Why Does CHF Increase? (7)
Observed CHF enhancement magnitude is consistent
with theory prediction
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Nuclear Applications of Nanofluids

1. PWR main coolant. Coolant chemistry and particle
   deposition are big concerns
2. Safety systems. Requires also post-CHF
   enhancement (not proven yet)
3. In-vessel retention for high-power density
   reactors. Very promising

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In-Vessel Retention
Use of a nanofluid results in a stable 40 heat
removal enhancement with the same margin to DNB
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In-Vessel Retention (2)
Concentrated nanofluid is injected in already
flooded reactor cavity, thus creating a dilute
nanofluid
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In-Vessel Retention (3)
Mean particle diameter in alumina nanofluid, as
measured with DLS
Little agglomeration occurs after
dilution Nanofluid stays stable for at least 24
hours after dilution
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Conclusions

• Nanofluids offer potential for significant
  enhancement of the boiling critical heat flux
• Nuclear applications include PWR primary coolant,
  safety systems, in-vessel retention
• MIT is conducting a multi-disciplinary research
  program to investigate heat transfer enhancement
  in nanofluids

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Future Work
Flow boiling