Investigations on the pool boiling heat transfer and critical heat flux of ZnO-ethylene glycol nanofluids

Surfactant free and fairly stable ZnO-ethylene glycol (EG) nanofluids are prepared using prolonged sonication (>60 h). Extended period of sonication results in superior fragmentation and dispersion of ZnO nanoparticles, as is evident from the DLS data. Thermal conductivity of the prepared nanofluid displays a maximum enhancement of 40% for 3.75% volume fractions of ZnO loading in EG at 30 °C. The nucleate pool boiling heat transfer characteristics of ZnO-EG nanofluids with various loading of ZnO nanoparticles are measured at atmospheric pressure employing a cylindrical polished copper heater surface. The boiling heat transfer coefficient enhances with ZnO concentration and attains a maximum of 22% compared to that of base fluid for ZnO volume fraction of 1.6%. However, further loading of ZnO nanoparticles in EG decreases the heat transfer coefficient. Critical heat flux measurements are performed with a thin Constantan wire. CHF value appreciably increases with increasing ZnO loading and displays a maximum enhancement of ∼117% for nanofluid containing 2.6% volume fractions of ZnO.