Development of a correlation for pressure drop of two-phase flow inside horizontal small diameter smooth and microfin tubes

This study investigated the pressure drop of adiabatic vapor-liquid two-phase flow inside horizontal smooth and microfin tubes with 2.5 mm outside diameter. R134a and R1234yf were used as working fluid and the experiments were carried out at saturation temperatures of 20 and 30 degrees C, mass velocities ranging from 50 to 200 kg m(-2) s(-1) and vapor qualities ranging from 0.1 to 0.9. The effects of mass velocity, vapor quality, refrigerant properties and tube diameter on the pressure drop were analyzed. Some typical previous pressure drop correlations were used to predict the experimental data. A new two-phase pressure drop correlation for small diameter tubes was proposed based on the experimental data. The new correlation agrees with the available other researchers' data and it can be broadly applied to the small diameter smooth and microfin tubes, wide range of mass velocity and many kinds of refrigerants. (C) 2020 Elsevier Ltd and IIR. All rights reserved.