Condensation heat transfer and pressure drop in flattened smooth tubes having different aspect ratios

In this study, condensation heat transfer coefficients of R-410A are obtained in flattened stainless tubes made from 5.0 mm inner diameter round tubes. The test range covers saturation temperature 45°C, heat flux 10 kW/m2, mass flux 100∼400 kg/m2s and quality 0.2∼0.8. Results showed that the effect of aspect ratio on condensation heat transfer coefficient appears to be dependent on the flow pattern. For annular flow, the heat transfer coefficient increases as the aspect ratio increases. For stratified flow, however, reverse is true. The pressure drop always increases as aspect ratio increases. Round tube heat transfer correlations were not successful in predicting the flat tube heat transfer data. Modified Shah correlation is proposed, which predicts the data with 18% RMS error. The pressure drop is reasonably predicted by Muller-Steinhagen and Heck or Friedel correlation (22% and 27% RMS error respectively).

► Condensation heat transfer and pressure drop data obtained in progressively flattened tubes using R410A.
► Test range covers mass flux 100∼400 kg/m2s, and saturation temperature 45°C.
► Effect of aspect ratio on condensation heat transfer coefficient depends on flow pattern.
► Existing round tube correlations do not adequately predict the heat transfer coefficients and a new correlation is provided.
► Pressure drops are properly predicted with existing round tube correlation.