Enhancement of pool boiling heat transfer in water by means of the introduction of free particles on the heated surface is investigated. The layer of loose particles on the heated surface is free to move and deform under the action of bulk liquid convection and vapor nucleation. High-speed visualizations show that bubble nucleation preferentially occurs at the narrow corner cavities formed between the free particles and the heated surface. The effects of the number and size of the free particles are experimentally explored using copper particles over a wide size range from tens of nanometers to 13 mm. Experimental results show that a mixture of free particle diameters of 3 mm and 6 mm provides the greatest improvement in boiling heat transfer, resulting in an average increase in heat transfer coefficient of 115% relative to a baseline polished surface without particles. A numerical heat transfer simulation and an analytical force balance model are developed to predict nucleation incipience and explain the parametric trends in boiling performance observed in the presence of the free particles.
Phase change, free particles, pool boiling enhancements, nucleation, water
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