Experimental investigation of condensation heat transfer on hybrid wettability finned tube with large amount of noncondensable gas

Condensation heat transfer outside horizontal plain and finned tubes with different surface wettability is experimentally studied. The methods of self-assembled monolayer coatings of n-octadecyl mercaptan with oxidation and etching treatments are employed to create the hydrophobic surfaces or superhydrophobic surfaces with nanostructures. The hydrophilic-hydrophobic (HH) hybrid and the hydrophilic-superhydrophobic (HS) hybrid surfaces based on the finned tubes are fabricated as well. The experimental results show that the HS hybrid finned tube achieves the highest condensation heat transfer performance in the presence of a large amount of noncondensable gas while it does not exhibit superior performance for the pure vapor condensation. The fraction of water vapor in the nitrogen-vapor mixture has significant influence on the condensation heat transfer coefficient. The dropwise condensation transforms gradually to the film condensation on both the superhydrophobic and the HS hybrid finned tubes with the increase of water vapor fraction. (C) 2015 Elsevier Ltd. All rights reserved.