Evaporation heat transfer and pressure drop of R-410A in flattened smooth tubes having different aspect ratios

In this study, evaporation heat transfer coefficients and pressure drops of R-410A were obtained in flat tubes. Flat tubes were made by progressively deforming 5.0 mm I.D. round tube. The test range covered mass flux 200–400 kg m−2 s−1, heat flux from 5 to 15 kW m−2 and saturation temperature from 10 to 15 °C. Results show that both evaporation heat transfer coefficients and pressure drops increased as aspect ratio increased, and were reasonably predicted by appropriate round tube correlations. It is shown that usage of equivalent diameter than hydraulic diameter yields better prediction of heat transfer coefficient. For pressure drop, however, the success is dependent on the correlation.