A UNIFIED MODEL FOR THE PREDICTION OF BUBBLE DETACHMENT DIAMETERS IN BOILING SYSTEMS .2. FLOW BOILING

An improved model is proposed for the prediction of departure and lift -off diameters in saturated forced convection boiling. The model utili zes a force balance similar to that proposed by Klausner et al. (Int. J. Heal Mass Transfer 36, 651-662 (1993)). One significant improvement is that the inclination angle is determined on a dynamic basis and is not required as an input. Furthermore, it is hypothesized that the su rface tension force is small compared to other forces acting on a vapo r bubble at the points of departure and lift-off, and thus information on the bubble contact diameter and contact angles is not required. A new data set on mean vapor bubble lift-off diameters and probability d ensity functions (pdf's) for flow boiling of refrigerant R 1 13 on a n ichrome heating strip has been obtained using the experimental facilit y described by Klausner et al. (Int. J. Heat Mass Transfer 36, 651-662 (1993)). The wall superheat and mean liquid velocity respectively ran ge from 5.5 to 12.0-degrees-C and 0.35 to 1.0 m s-1. It is demonstrate d that over the limited range of flow boiling conditions considered, t he predicted departure and lift-off diameters agree well with measured values.