The effect of micro/nanoporous inside surface coated vertical tubes on CHF was determined during water flow boiling at atmospheric pressure. CHF was measured for smooth and three different coated tubes, at mass fluxes (100-300 kg/m(2) s) and two inlet subcooling temperatures (50 degrees C and 75 degrees C). Greater CHF enhancement was found with microporous coatings than with nanoporous coatings. Al2O3 microporous coatings with particle size < 10 mu m and coatings thickness of 50 mu m showed the best CHF enhancement. Maximum increase in CHF was about 25% for microporous Al2O3. A wettability test was performed to study an increase of CHF with microporous coated surfaces. (c) 2006 Elsevier Ltd. All rights reserved.