SUPPRESSION OF FLOW BOILING NUCLEATION

A simple model is presented for estimating the ratio of the maximum to minimum cavity radius required for ebullition in two-phase flow with heat transfer. The resulting dimensionless parameter, r(max)/r(min), i s demonstrated to correlate flow boiling nucleation site density. As t he convective heat transfer associated with bulk turbulence in two-pha se flow is enhanced, r(max) --> r(min), and the probability of finding surface cavities whose radii lie between r(max) and r(min) is reduced . Thus, active nucleation sites become deactivated. A vertical flow bo iling facility was fabricated in which the nucleation suppression poin t can be measured. Experiments conducted for mass flux ranging from 18 3-315 kg/m(2)-s and inlet quality ranging from 0-0.151, along with dat a available from the literature, suggest that r(max)/r(min) is the lea ding order dimensionless parameter on which the complete suppression o f nucleation sites depends. Although the suppression of nucleation sit es also depends, to a certain extent, on the surface/fluid combination and heatflux, it is found that complete suppression occurs for r(max) / r(min) ranging from 40 to 120. This is proposed as a criterion to di scriminate the purely, convective regime from the nucleate boiling reg ime.