Transient critical heat fluxes in subcooled pool boiling of FC-72

Critical heat fluxes (CHFs) in a pool of Fluorinert FC-72 were measured for period from transient heat inputs up to steady-state ones. Measurements were made using 1.0 mm diameter of platinum and gold horizontal cylinders in wide ranges of liquid subcoolings and pressures. The steady-state CHF for saturated condition almost agree with the hydrodynamic instability (HI) model. However, in higher subcoolings, the increasing rate of steady-state CHFs is lower than HI model and it was suggested due to the heterogeneous spontaneous nucleation (HSN). The CHFs for period are clearly categorized into the first, second, and third groups for long, short, and intermediate periods, respectively. Transient CHFs on semi-direct and direct transitions from non-boiling heat conduction to film boiling, exist predominantly during short periods. Those transient processes were assumed due to the explosive-like HSN in originally flooded cavities on cylinder surface. Each of the steady-state and transient CHFs that were obtained from both heaters in various liquid subcoolings and pressures, generally well agree each other. (author)