Condensation heat transfer characteristics were studied experimentally using R410A for a mass flow range of 250∼450 kg m-2 s-1 and saturation temperature of 45°C in order to determine the performance of smooth and enhanced heat transfer tubes. Visual flow patterns under condensation conditions were observed in horizontal tubes. Smooth tube condensation flow patterns are consistent with the predicted flow patterns from previous investigations and heat transfer performance in enhanced tubes were compared with the performance found in smooth tubes. The condensation heat transfer enhancement ratio for the enhanced tubes are: 1.15∼2.05 (Vipertex model 1EHT tube), and 1.18∼1.69 for a Helix tube (HX) tube. In addition, the material thermal conductivity of a smooth tube has a small influence on its heat transfer performance; greater enhancement was found in the enhanced tubes. Stratified wavy flow (SW), intermittent flow (I), semi-annular flow (SA) and annular flow (A) were observed in the range evaluated.
The heat transfer coefficient increases with an increase of mass velocity. When the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner. This reduces the thermal resistance and enhances heat transfer; heat transfer performance for low mass velocities rise slowly. The performance improvement at high mass flux rates is greater than that at low mass flux rates. Better heat transfer performance is shown for tube wall materials with high thermal conductivity and/or tubes with smaller diameters.