Optimum fin geometries on condensation heat transfer and pressure drop of R1234ze(E) in 4-mm outside diameter horizontal microfin tubes

This study experimentally investigated the condensation heat transfer and pressure drop characteristics of R1234ze(E) inside horizontal small-diameter (4.0-mm) microfin tubes with three different types of fin geometries. The three fin geometries were as follows: 40 fins with a fin height of 0.18 mm and a helix angle of 18 degrees, 50 fins with a fin height of 0.15 mm and a helix angle of 12 degrees, and 50 fins with a fin height of 0.12 mm and a helix angle of 25 degrees. The experiments were carried out for a range of mass velocities from 50 to 400 kg m(-2) s(-1) and at a saturation temperature of 35 degrees C. The heat transfer coefficient of the microfin tubes was compared to those of smooth tubes and was evaluated in terms of the heat transfer enhancement factor. The effects of different fin geometry parameters, such as the number of fins, fin height, and helix angle, on the heat transfer and pressure drop were investigated. The heat transfer coefficient increased at 50 kg m(-2) s(-1) as the number of fins increased. Fin height exerted the greatest influence on heat transfer enhancement at 200 kg m(-2) s(-1). The measured heat transfer coefficient and pressure drop were compared with previous correlations, and the practical effectiveness of the results was verified in terms of the previous our correlations for small-diameter microfin tubes.