Pressure drop during condensation and vaporisation of refrigerants inside enhanced tubes.

The most interesting enhanced tubes for inside condensation and vaporisation are low-fin and micro-fin tubes because they present a marked improvement in heat transfer with small penalty in pressure losses: the aim of this work is to investigate pressure drops inside horizontal finned tubes. Two traditional models for adiabatic pressure losses inside smooth tubes (Friedel and Sardesai et al.) were modified for condensation and vaporisation inside enhanced tubes by a specific correction which accounts for the effects of micro-fins. These modified models were compared against the available experimental data which includes condensation and boiling of traditional refrigerants (R12, R22, R32, R502), new refrigerants (R134a) and also zeotropic and nearly-azeotropic refrigerant mixtures (R407A, R407C, R404A, R410A) in a wide range of tube geometries and operative conditions.