Nucleate and convective boiling in plate fin heat exchangers

The results of laboratory experiments with CFC114 flowing in an electricall y heated, serrated-fin or perforated fin test section to measure local boil ing coefficients over a wide range of vapour quality, with mass fluxes up t o 45 kg/ m(2) s, heat fluxes up to 3500 W/m(2) and pressure of 3 bar are re ported. These low mass and heat fluxes reflect the industrial process appli cation of these heat exchangers where small temperature differences may exi st between streams. An analysis of the measured heat transfer coefficients from tests with CFC1 14 in both serrated fin and perforated fin geometries shows the separate ef fects of quality, mass flux and heat flux. Two kinds of mechanism were found: a nucleate boiling regime and a convecti ve boiling regime. The data were predicted using an asymptotic model, the n ucleate boiling component was obtained from pool boiling data and the force d 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)]. (C) 2000 Elsevier Science L td. All rights reserved.