Boiling heat transfer and flow characteristic of R32 inside a horizontal small-diameter microfin tube

This study experimentally investigated the flow boiling heat transfer and pressure drop characteristics of R32 inside a horizontal small-diameter microfin tube with an equivalent diameter of 3.48 mm. The boiling heat transfer coefficient and pressure drop were measured in a mass velocity range of 50-400 kgm(-2) s(-1), heat flux range of 5-20 kWm(-2), and saturation temperature of 15 degrees C. The flow pattern at the outlet of the test microfin tube was observed and classified as wavy-slug flow and annular flow regime. The effects of quality, mass velocity, heat flux, and flow pattern on the flow boiling characteristics were clarified. The heat transfer mechanism was characterized by forced convection, nucleate boiling, and evaporation heat transfer through the thin liquid film inside the grooves. No difference in the frictional pressure drop on adiabatic and boiling flows was observed. The measured heat transfer and frictional pressure drop were compared with those in previous correlations. (C) 2018 Elsevier Ltd and IIR. All rights reserved.