Local heat transfer coefficients are predicted for turbulent water subcooled flow boiling through uniformly heated circular tubes. Correlations by Petukhov and by Shah are modified slightly. However, the correlation suggested by Kandlikar is improved significantly by requiring that it approach more accurate limits near the onset of fully developed boiling and the onset of nucleate boiling for subcooled flow. Excellent agreement is obtained with data corresponding to conditions of high inlet subcooling (183°C), high mass velocity (4.4 to 31.5 Mg/m2·s), and a large ratio of the axial coordinate to the diameter (95.5). The exit subcooling varies from 53.0 to 81.5°C. For smaller ratios (<50.0), the accuracy decreases. In all cases, the local film temperature is the characteristic temperature. When the associated critical heat flux (CHF) data are examined in a Stanton number-Peclet number space, St < 0.0065 and Pe > 105 in all cases. Comparisons with the Saha-Zuber criterion for bubble detachment show that moderately subcooled and high-velocity flows are characterized by a multiboundary layer phenomenon that includes an attached bubble layer. These results show that the bubble layer's existence can now be documented for a wide variety of fluids and conditions without flow visualizations. Unlike the hydrodynamic liquid separation initiated CHF suggested by Tong and Kutateladze, the present sparse evidence seems to point to a localized liquid dry out due to bubble crowding. In this case, the locus of the CHF (a) is very near the boundary for the onset of fully developed flow boiling and (b) follows similar trends of the boundaries for the onset of nucleate and fully developed flow boiling.