Nucleate and convective boiling in plate fin heat exchangers

The results of laboratory experiments with CFC114 flowing in an electrically heated, serrated-fin or perforated fin test section to measure local boiling coefficients over a wide range of vapour quality, with mass fluxes up to 45 kg/m2 s, heat fluxes up to 3500 W/m2 and pressure of 3 bar are reported. These low mass and heat fluxes reflect the industrial process application of these heat exchangers where small temperature differences may exist between streams. An analysis of the measured heat transfer coefficients from tests with CFC114 in both serrated fin and perforated fin geometries shows the separate effects of quality, mass flux and heat flux. Two kinds of mechanism were found: a nucleate boiling regime and a convective boiling regime. The data were predicted using an asymptotic model, the nucleate boiling component was obtained from pool boiling data and the forced convective component of the two-phase heat transfer coefficient was found to be well represented by the F and Martinelli parameters used by Chen [I&EC Process Design and Development 5(3) (1966)].