Determination of Pool Boiling Critical Heat Flux Enhancement in Nanofluids

Nanofluids are engineered colloids composed of nano-size particles dispersed in common fluids such as water or refrigerants. Using an electrically controlled wire heater, pool boiling Critical Heat Flux (CHF) of Alumina and Silica water-based nanofluids of concentration less than or equal to 0.1 percent by volume were measured. Silica nanofluids showed CHF enhancement up to 68% and there seems to be a monotonic relationship between nanoparticle concentration and magnitude of enhancement. Alumina nanofluids had CHF enhancement up to 56% but the peak occurred at the intermediate concentration. The boiling curves in nanofluid were found to shift to the left of that of water and correspond to higher nucleate boiling heat transfer coefficients in the two-phase flow regime. SEM images show a porous coating layer of nanoparticles on wires subjected to nanofluid CHF tests. These coating layers change the morphology of the heater's surface, and are responsible for the CHF enhancement. The thickness of the coating was estimated using SEM and was found ranging from 3.0 to 6.0 micrometers for Alumina, and 3.0 to 15.0 micrometers for Silica. Inductively Coupled Plasma Spectroscopy (ICP-OES) analyses were also attempted to quantify the mass of the particle deposition but the results were inconsistent with the estimates from the SEM measurement. Thesis Supervisor: Jacopo Buongiorno Title: Assistant Professor of Nuclear Science and Engineering Thesis Supervisor: Lin-Wen Hu Title: Associate Director of the MIT Nuclear Reactor Laboratory ACKNOWLEDGMENTS: First, I would like to thank Professor Jacopo Buongiorno and Dr. Lin-wen Hu, my thesis advisors, for their support and guidance. Their advices, questions and inputs were useful and important for this project. In addition, I want thank Dr. Thomas McKrell who helped me with the experiments all this time. His suggestions, especially for the post CHF experiment analyses, were always valuable. Also, I want to thank graduate student Sung Joong Kim, with whom I had many insightful discussions. Thank you to Eric Forrest, my undergraduate fellow, who helped me with the particle's size measurement. Finally, I want to thank my family, and all my friends, especially Jennifer Choy, who have always been there and have supported me for the last four years.