A general nonlinear equation for estimating the frictional pressure drop during condensation of fluids in different mini/micro and macro channels was obtained using the genetic programming (GP). The developed model is similar to that of the Lockhart and Martinelli [1] model. For developing the new correlation, 7328 data points were collected from 35 sources, which cover a wide range of fluids, channel geometries, diameters, mass fluxes, and saturation temperatures for single-port and multi-port channels. The newly developed correlation for the two-phase flow predicted a wide range of conditions with an average absolute relative deviation (AARD) of 22.92%. The same database was used for the evaluation of the available empirical correlations. Their deviations were significantly higher than that of the new correlation.
