CHF enhancement of Al2O3, TiO2 and Ag nanofluids and effect of nucleate pool boiling time

Abstract

Nanofluids are nanometer sized suspended particles in water or other base fluids. They are used for their increased nucleate boiling critical heat flux (CHF) values far beyond compared to pure water or base fluid. Therefore pool boiling heat transfer tests are performed to understand increase in CHF. The pool boiling characteristics and critical heat flux enhancement using nanofluids of dilute dispersions of alumina, titania and silver are studied. High heat transfer rates with high critical heat flux achieved with modest nanoparticle concentrations (<;0.1% by volume). Heater wire used in CHF tests were only on 50μm in diameter. Change in surface structure of heater wire causes increase in CHF. Surface of the heater is covered with porous layer of nanoparticles during nucleate boiling. It is determined to investigate the effects of nucleate boiling time (coating time) during which the heater wire is exposed to deposition of nanoparticles. Results of this study presented that there is a non-linear relationship between the coating time and CHF for short periods of coating times, up to 30 seconds; however this effect loses its impact if the coating duration is elongated. It was also showed that longer periods of coating time increased the CHF but not drastically and the relationship between coating time and CHF is no longer non-linear and can be approximated by a linear line. This study represents an important step in understanding the relationship between CHF and the optimum amount of nanoparticle deposition or amount of porous layer of nanoparticles formed on heater surface with respect to nucleate boiling (coating)/time dependency.