Outline - PowerPoint PPT Presentation

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

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

Aluminum Oxide Particles in Water

• 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%)

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

Measured thermal conductivity of >20 nanofluids with transient hot wire technique

No abnormal thermal conductivity enhancement observed

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

Water-based nanofluid with ZrO2 particles

DI water (1 MW/m2)

DI water (0.5 MW/m

)

2

Nanofluid (1 MW/m

)

2

Nanofluid (0.5 MW/m2)

Very significant CHF enhancement observed at low nanoparticle concentrations

Why Does CHF Increase?

• Thermophysical properties do not change significantly at low nanoparticle concentration

Al

EDS: 0.01v% Al2O3

SEM Picture of SS316 Wire

After Boiling of 0.01v% Al2O3 Nanofluid

SEM Picture of SS316 Wire

After Boiling of DI Water

• Heater surface does change upon nanofluid boiling!!

Measurements of nanoparticle deposition on heated surface during boiling

Plate Type Heater – SS316

SEM: Clean SS316 Surface

EDS: Clean SS316 Surface

SEM: 0.01v% Al2O3

Al

SEM: 0.01v% SiO2

100 m

EDS: 0.01v% Al2O3

Si

Zr

SEM: 0.01v% ZrO2

100 m

EDS: 0.01v% SiO2

EDS: 0.01v% ZrO2

100 m

Pure water on clean surface

Nanofluid on clean surface

Pure water on nanoparticle fouled surface

Nanofluid on nanoparticle fouled surface

Surface wettability increases dramatically

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

Why Does CHF Increase? (7)

Observed CHF enhancement magnitude is consistent with theory prediction

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

Use of a nanofluid results in a stable +40% heat removal enhancement with the same margin to DNB

Concentrated nanofluid is injected in already flooded reactor cavity, thus creating a dilute nanofluid

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

• 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

Future Work

Flow boiling