Nanoscale modification of key surface parameters to augment pool boiling heat transfer and critical heat flux in water and dielectric fluids

Abstract

Surface effects on pool boiling heat transfer and the critical heat flux are well documented but poorly understood. This study investigates the pool boiling characteristics of various fluids, and demonstrates that surface effects can drastically alter the nucleate boiling heat transfer coefficient as well as the critical heat flux. Changes in surface morphology and surface chemistry are suspected to be the primary factors influencing pool boiling heat transfer. The relative impact of surface properties is shown to depend strongly upon the working fluid. To evaluate the effects of chemical constituency and surface texture on the pool boiling of water, nanoparticle thin-film coatings are applied to nickel and stainless steel substrates using the layer-by-layer assembly method. This study shows that such coatings, with thicknesses on the order of one micron or less, are capable of enhancing the critical heat flux of water up to 100%, and enhancing the nucleate boiling heat transfer coefficient over 100%. Through the use of thin-film coatings, the importance of nanoscale surface texture, porosity, and chemical constituency on boiling mechanisms is revealed. Low surface tension dielectric fluids, including a recently developed fluorinated ketone with a low global warming potential, are tested to determine their pool boiling heat transfer capabilities. The potential for nanoparticle-based pool boiling enhancement in well-wetting dielectric fluids is investigated. The role of surface wettability and adhesion tension on the incipience of boiling, nucleate boiling, and critical heat flux are considered.

(cont.) Results indicate that the low global warming potential fluorinated ketone may be a viable alternative in the cooling of electronic devices. Additionally, results demonstrate that enhancement of boiling heat transfer is possible for well-wetting dielectric fluids, with 40% enhancement in the critical heat flux using dilute suspensions of aluminum or silica nanoparticles in the fluorinated ketone.