An experimental investigation on periodic single bubble growth and departure from a small heater submerged in a nanofluid containing moderately hydrophilic nanoparticles

An experimental investigation is carried out on periodic single bubble growth and departure from a small heater in boiling of nanofluids. The nanofluids are made of moderately hydrophilic silica nanoparticles (having a contact angle of 35-37 degrees), dispersing in deionized water at mass concentrations of 0.05%, 0.1% and 0.15%, respectively. It is found that the bubble departure frequency and boiling heat transfer by latent heat are enhanced with increasing concentration of moderately hydrophilic silica nanoparticles. However, the periodic single bubble departure diameter is not affected by the presence of moderately hydrophilic silica nanoparticles significantly. After boiling experiments of these nanofluids are carried out, it is found that a larger amount of moderately hydrophilic silica nanoparticles are deposited on the heater surface at higher wall heat flux, the morphologies of the small deposition layers are varied with increase of heat flux or concentration. The reason for increasing amount of nanoparticles deposited on the heater surface as the wall heat flux is increased is verified by an analysis of vapor recoil force acting on a moderately hydrophilic nanoparticle at the vapor/liquid interface near the wall.