Microchannel (D-h <= 100 mu m) water flow boiling under low mass flux (G <= 138.9 kg/(m(2) s)) is presented to investigate the local phenomena of flow regime development and nucleating bubble growth rate. During horizontal flow, onset of nucleation, flow regime, and isolated single bubble growth and detachment from a single artificial cavity were observed and analyzed by microscopic high-speed visualization under various flow rates and wall superheat conditions. Results showed that while the predictions pertaining to inception by bubble nucleation theory match well, bubble growth rate, detachment and expansion in a microchannel differs dramatically from a macrochannel. (C) 2011 Elsevier Ltd. All rights reserved.