Effects of thickness of boiling-induced nanoparticle deposition on the saturation of critical heat flux enhancement

Pool boiling tests were conducted to determine the effects of nanoparticle coating thickness on critical heat flux in 0.01 vol.% alumina nanofluid under atmospheric pressure using Ni-Cr wire heaters. The thickness of nanoparticles coating layer was controlled by varying the boiling time for pre-coating in the nanofluid. The CHF enhancement curve was acquired with respect to time of pre-coating process. As the result, the CHF enhancement is remained or saturated regardless of boiling time over certain or critical pre-coating time while the CHF sharply increased in relatively shorter pre-coating time. The CHF is gradually decreased after the critical time region. The wetting characteristics and the Taylor wavelengths on the coating surfaces were investigated to explain the trend of CHF regarding the effects of coating thickness. The physical deposition characteristics such as the coating thickness and the porosity were studied to analyze the CHF trend. The porosity is a key parameter to determine the CHF saturated under conditions over a critical coating thickness. (C) 2014 Elsevier Ltd. All rights reserved.