Heat Transfer Behavior of Oxide Nanoparticles in Pool Boiling Experiment

Abstract

The heat transfer characteristics of silica (SiO2), ceria (CeO2), and alumina (Al2O3) nanofluids at 0.5% concentration and particle size of 10nm and 20 nm in pool boiling have been analyzed. The influence of acidity on heat transfer has been studied. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles, their mutual interactions towards the wire. When there is no particle deposition on the wire, the nanofluid with any oxide suspension increases CHF by about 50% within uncertainty limits regardless of the type of the oxide particle and its size. The extent of oxidation on the wire impacts CHF, and is influenced by the chemical composition of nanofluids in buffer solutions. Amorphous oxides (SiO2) are generally more disordered and less closely packed compared to the crystalline oxides such as CeO2 and Al2O3. The arrangement of the atoms within the unit cell and the layer of water molecules at the surface possibly influence the natural convection as well as the CHF. The boiling regime is further extended to higher heat flux when there is agglomeration on the wire. This agglomeration allows high heat transfer through interagglomerate pores, resulting in a nearly 3-fold increase in CHF. This deposition occurs for the charged 10 nm silica particle, and was not seen for other oxide particles. The chemical composition, oxidation and packing of the particles within the deposition on the wire are shown to be the reasons for the extension of the boiling regime and the net enhancement of the Critical Heat Flux.