10.1063/5.0070494.1

Abstract

The present study investigates the underlying mechanisms of nanoparticle deposition during nucleate pool boiling on plain hydrophobic surfaces. Single bubble pool boiling experiments with water and two concentrations of SiO2-water nanofluids have been conducted under saturated conditions. Indium tin oxide-coated sapphire has been employed as the substrate surface. Infrared (IR) thermography has been used to map the temperature and heat flux distributions underneath the vapor bubble to identify the mechanisms responsible for imparting an orderly pattern to nanoparticle deposition. Optical characterization of nanoparticle-deposited substrates showed a distinct circular porous structure of the deposited nanoparticles at the nucleation site and almost negligible deposition away from it for both the nanofluid concentrations. Temperature and heat flux contour plots indicated toward the ceasing of microlayers for water-based experiments and existence of microlayers for nanofluids. The observed nature of the nanoparticle deposited layer has been attributed to the prevalent bubble base evaporation mechanism. Interdependence between the bubble base evaporation mechanism and nanoparticle deposition has been discussed. An intriguing feature of the nanoparticle deposited structure in the form of a thin peripheral ring was identified, wherein larger micrometer-sized particles were found to be deposited along the ring while the smaller-sized nanoparticles were found in the inner core region. Plausible explanation(s) for the mechanisms associated with the observed size distribution of nanoparticles over the deposited structure have been provided. The IR thermography-based temperature data have been used for heat transfer partitioning. The analysis showed that the overall heat transfer coefficient decreases with nanofluids as compared to water as the working fluid.