Finally, the experimental frictional pressure gradient was compared against the values predicted by semi-empirical correlations. Fig. 14a shows AMD 3465 comparison between the experimental frictional pressure gradient and the values predicted by the correlation proposed by Han and Lee . This correlation was developed from measurements of the frictional pressure drops during condensation inside microfin tubes. The model was applied following the integral method as suggested by Mauro et al. . The correlation underestimates the frictional pressure drops with mean, absolute, and standard deviations of −20.9%, 24.0%, and 24.7%, respectively. Fig. 14b reports a comparison between the experimental pressure gradients and the values estimated by a correlation recently proposed by the present authors . The model is carpels valid for G > 190 kg m−2 s−1. The comparison is also extended to R134a data, taken from Mancin et al. . The model well predicts the frictional pressure drop, with a relative, an absolute, and a standard deviations of −6.0%, 8.8%, and 8.9%, respectively, for R1234yf, and of −0.2%, 8.5%, and 12.8%, respectively, for R134a.