Post critical heat transfer to flowing liquid in a vertical tube. Final report. [BWR]

The heat transfer characteristics of a liquid in vertical upflow in a tube in which the critical heat flux has been exceeded is investigated. Using a novel transient experimental technique the entire forced convection boiling curve for liquid nitrogen was obtained for a given mass flux-quality combination from which parametric effects of heater material, surface roughness and oxide scale, and dryout length on the dry wall film boiling region were determined. The results show that both increased roughness and oxide scale increase the post critical heat transfer. Increasing the dryout length decreases the heat transfer at a given mass flux-quality combination due to thermal nonequilibrium effects. No material effects were noted. (GRA)