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
Outline • Intro to nanofluids • MIT program research highlights • single-phase heat transfer • boiling heat transfer • Promising nuclear applications • Conclusions
Aluminum Oxide Particles in Water 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%)
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
Research Highlights
Nanofluid Thermal Conductivity Measured thermal conductivity of >20 nanofluids with transient hot wire technique No abnormal thermal conductivity enhancement observed
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
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 Nanofluid Critical Heat Flux
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 Why Does CHF Increase? (2) • Heater surface does change upon nanofluid boiling!!
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
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 Why Does CHF Increase? (4)
Pure water on clean surface Nanofluid on clean surface Pure water on nanoparticle fouled surface Nanofluid on nanoparticle fouled surface Why Does CHF Increase? (5) 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
Nuclear Applications of Nanofluids • 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
In-Vessel Retention Use of a nanofluid results in a stable +40% heat removal enhancement with the same margin to DNB
In-Vessel Retention (2) Concentrated nanofluid is injected in already flooded reactor cavity, thus creating a dilute nanofluid
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
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
Future Work Flow boiling
Download
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
