Critical heat fluxes for curved and straight surfaces during subcooled flow boiling

A total of 274 experiments were conducted at five mean velocities and four subcoolings. The analytical study and the experimental data indicate that for equal velocity and subcooling, concave surfaces sustain larger critical heat fluxes than straight surfaces which, in turn, sustain larger critical heat fluxes than convex surfaces. An idealized vapor bubble cycle was defined and is used as the basis for a critical heat flux model. In the model, vapor bubbles are assumed to depart from the heated surface when they have grown to the edge of the hydrodynamic sublayer. The frequency of the idealized vapor bubble cycle was derived and combined with expressions for the energy associated with each vapor bubble cycle and the number of active sites present to produce a critical heat flux expression. The resulting expression contains only one empirical constant.