This study explores critical heat flux in flow boiling of de-ionized water at high mass fluxes in similar to 249 gm and similar to 494 mu m inner diameter tubes, which are heated along short heated lengths (2-10 mm). Ultra high heat flux cooling (>10,000 W/cm(2)) is achieved in microscale at high mass fluxes (>10,000 kg/m(2)s). Input heating powers were measured and processed to obtain critical heat fluxes (CHF). It was shown that high heat removal rates more than 30,000 W/cm(2) were attained with a reasonable combination of working conditions (short heated length-high mass flux-small hydraulic diameter), which can be proposed as a promising solution method for possible new emerging applications such as nano-scale plasmonic applications, near field radiative energy exchange between objects, and nano thermophotovoltaics. Experimental results were compared with the existing CHF prediction methods recommended for low quality flow boiling, and new correlations for predicting CHF were proposed. (C) 2012 Elsevier Masson SAS. All rights reserved.