Focusing on the effects of a liquid velocity and subcooling, in this study the foced-convective film-boiling heat transfer was examined experimentally and analytically. Quenching tests of a vertical-long-thick cylindrical pipe were conducted for subcooled R-113 liquid in a range of bulk-liquid velocities from 0.018 to 0.081 m/s at a pressure of 0.1 MPa. The test section made of pure copper was 50, 15 and 110 mm in outer diameter, thickness and height, respectively. The test section was inserted into a transparent Pyrex glass pipe concentrically, and an annular flow passage was formed between the glass pipe and the test section.
Measured heat transfer coefficients were higher than those predicted with the two-phase boundary layer theory even in a low liquid velocity region. The characteristics of the measured heat transfer coefficients were quite similar to those of the pool film boiling. The vapor-film-unit model developed for the natural-convective film boiling was extended and applied to the present conditions. In the model, the Kelvin-Helmholtz instability wave length was used to give the length scale of the unit. The model provided good agreement with the experimental results.