The quenching characteristics of metallic rodlets and spheres were investigated in pure water and water-based nanofluids with alumina nanoparticles of 0.1% by volume. The experiments were performed at both saturated and subcooled conditions under atmospheric pressure. The results demonstrate that while the initial quenching behavior in nanofluids is identical to that in pure water, both the minimum heat flux point temperature and quench front speed are significantly enhanced in subsequent quenching repetitions due to nanoparticle deposition. The nanoparticle effects on the quenching process were analyzed with focus on the intermittent liquid-solid contacts in the film boiling regime. It appears that the liquid-solid interaction during such short-lived contacts is more vigorous when a nanoparticle layer with improved surface wettability and roughness is present, which leads to the premature disruption of film boiling and quenching acceleration. (C) 2009 Elsevier Ltd. All rights reserved.