Department of Mechanical Engineering, IIT Bombay, Mumbai-400076, India
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai
Influence of varying concentration of nanofluid on bubble growth dynamics and associated microscopic bubble base evaporation mechanisms has been investigated on hydrophobic surface. Single bubble-based nucleate pool boiling experiments with water and two volumetric concentrations (0.0025% and 0.005%) of SiO2-water nanofluids have been conducted under saturated bulk and constant applied heat flux conditions. The bubble growth dynamics and the associated wall heat transfer mechanisms have been mapped simultaneously by coupling two non-intrusive measurement techniques, namely high speed videography and IR thermography. The recorded videographic and IR images revealed that the growth dynamics and the bubble base evaporation mechanism associated with the single vapor bubble gets changed dramatically in the case of the nanofluids as compared to that observed for water experiments. The heat transfer partitioning analysis performed at micro/macroscopic levels showed that the overall heat transfer decreases with increasing concentration of nanofluids. However, the microlayer evaporation was found to result in higher heat transfer coefficient than that obtained with pure contact line evaporation-driven mechanism. The observed changes in the bubble growth dynamics and the bubble base evaporation mechanism for nanofluids compared to water have been attributed to the modification of the substrate surface properties caused due to deposition of a thin porous layer of nanoparticles underneath the vapor bubble.