Nanofluid pool boiling heat transfer phenomenon

The purpose of this paper is to explain how concentration of nanofluid, roughness and range of heat flux affect the boiling heat transfer coefficient. The boiling heat transfer coefficient was measured on rough and smooth heated substrates inside water and alumina nanofluid with different concentrations. The heated substrate was observed to be covered by a tiny porous layer of deposited nanoparticles and modified the size of cavities and boiling heat transfer coefficient. In case of smooth heated surface, the roughness, nucleation site density and consequently boiling heat transfer coefficient were enhanced because the size of deposited nanoparticles was bigger than surface roughness. The difference between heat transfer coefficient of alumina nanofluid and water was observed to decrease with heat flux, since big cavities were active to create nucleation in low heat fluxes and the smaller cavities were active only in high heat fluxes. The size of deposited nanoparticles was also observed to increase with concentration of nanofluid and play a significant role on variation of size of cavities in rough surfaces. The roughness of the heated substrate was observed to increase while the size of deposited nanoparticles was bigger than size of cavities. In addition, the effects of suspended nanoparticles on behavior of triple line were investigated, using bubble formation method. The suspended and deposited nanoparticles were observed to have a significant role to modify the dynamics of triple line and bubble growth. (C) 2015 Elsevier B.V. All rights reserved.