An Experimental Study of Surface Tension-Dependent Pool Boiling Characteristics of Carbon Nanotubes-Nanofluids

This paper reports an experimental investigation of the pool boiling heat transfer characteristics of single-walled carbon nanotubes (SWCNTs)-nanofluids. Two main characteristics were studied to identify their influence on boiling heat transfer: one is the surface tension through the addition of surfactant and the other is the chemical treatment of nanotubes sidewalls (i.e. oxidized and untreated sidewalls). A Transmission Electron Microscope was used to study the morphology of the functionalized nanotubes and their deposition on heater wire. The maximum enhancement of both the critical and burnout heat fluxes of this nanofluid over those of the pure deionized water are found to be 492% and 265%, respectively at a surfactant to carbon nanotubes concentration ratio of 1:5. This indicates that high enhancement of heat flux is possible and would depend on the concentration of the surfactants. Present results also demonstrate that CNT-nanofluids in a pool boiling environment can extend the saturated boiling regime and the burnout of the heated surface. The burnout heat flux is found to be a strong function of the relaxation of nanofluid surface tension with the base fluid. Based on the best fit of experimental data, an empirical correlation between the burnout heat flux of nanofluid and its relaxation of surface tension is introduced.