Experimental investigation of convective condensation heat transfer on tube bundles with different surface wettability at large amount of noncondensable gas

• Air–vapor condensation on tube bundles with various wettability is studied experimentally.
• The discrete droplet flow of the condensate among bundles is observed.
• Average condensation heat transfer improves as the tube-row number increases.
• Condensation enhancement of bundle effect reduces with increase of water vapor fraction.

Surface modification technology provides the potential to further enhance condensation heat and mass transfer. The water vapor convective condensation heat transfer of condensing heat exchanger assembled by plain, 2D-finned and 3D-finned tubes with different surface wettability was investigated experimentally, when the volume fraction of noncondensable gas was more than 75%. The condensation behaviors and flow patterns of the condensate among bundles were also recorded visually. It was found that the discrete droplet flow of condensate formed among tube bundles in the presence of large amount of noncondensable gas. Typical factors including the cooling water flow rate, air–vapor mixture flow rate, and the volume fraction of water vapor on convective condensation heat transfer coefficient were discussed in detail. The experimental results showed that the average condensation heat transfer coefficient of superhydrophobic plain tubes with 9 rows was 1.53 times of one single row for the water vapor volume fraction of 11% while it reduced to 1.34 times of one single row when the vapor volume fraction reached 23%.