ABSTRACT
A simple model is presented for estimating the maximum and minimum cavity radius required for ebullition in two-phase flow with heat transfer. It is demonstrated that the nucleation site density in flow boiling is correlated with the ratio of the maximum to minimum cavity radius, rmax/rmin, and the maximum cavity radius has a controlling influence. As the convective heat transfer associated with bulk turbulence in two-phase flow is enhanced, rmax/rmin→1, and the probability of finding surface cavities whose radii lie between rmax and rmin is reduced. Thus, active nucleation sites become deactivated. The value of rmax/rmin at which complete suppression of nucleation sites occurs, to a certain extent, depends on the surface/fluid combination and heat flux. For the available data, it is observed that complete suppression of nucleation sites occurs for rmax/rmin between 50 and 150. Various flow boiling heat transfer data sets have been examined, and it is found that many heat transfer data are not likely in the nucleate boiling regime.
