Condensation heat transfer characteristics of moist air outside a three-dimensional finned tube

The condensation heat transfer of moist air is a common phenomenon in industry processes, and improving the efficiency of condensation heat transfer is a common focus of research. Many studies have shown that extending the surface of the heat exchanger can effectively enhance the condensation heat transfer efficiency. Therefore, this study focused on a three-dimensional (3-D) finned tube heat exchange element with an extra-large extended surface, and experiments were conducted to study the condensation heat transfer characteristics of moist air outside the 3-D finned tube. The effects of different steam mole fractions, moist air velocities, cooling water inlet temperatures, and moist air temperatures on the condensation heat transfer characteristics of the moist air outside the 3-D finned tube were studied under atmospheric pressure. A smooth tube was also tested under the same conditions for comparison. The experimental results showed that the 3-D finned tube can achieve a higher heat transfer coefficient compared with the smooth tube under all tested conditions. Moreover, for both the 3-D finned tube and the smooth tube, the heat transfer coefficient increased with an increase in the steam mole fraction and moist air velocity, and decreased with an increase of moist air temperature or cooling water inlet temperature. Furthermore, in a single-phase convective heat transfer case, the 3-D finned tube could achieve 3.1 times the heat transfer coefficient of the smooth tube. In a moist air condensation heat transfer case, the 3-D finned tube could achieve 1.7 times the heat transfer coefficient of the smooth tube when the steam mole fraction was 0.05. Although the 3-D finned tube had a more serious condensate retention phenomenon compared with that of the smooth tube, the 3-D fins could still increase the heat transfer area and effectively break the flowing boundary layer outside the tube wall. In addition, the 3-D finned tube had a higher heat transfer coefficient compared with the smooth tube.