Aluminum substrate specimens are irradiated with nitrogen ions at various ion dose and ion energy levels in order to realize dropwise condensation on the specimen surfaces. Dropwise steam condensation initially occurs on these specimens, but the condensation mode changes into filmwise condensation. When the condensation mode changes to filmwise condensation, the heat transfer coefficient is measured to be approximately 40% lower than that predicted using the Nusselt theory; in addition, the color of the surface changes from yellow-brown to silver-white. This surface color change is the result of the hydrolysis reaction between the condensate and the nitrogen ion-implanted aluminum surface. Non-condensable gas is generated by the hydrolysis reaction, and this non-condensable gas diminishes the heat transfer coefficient. In addition, the material composition of the specimen’s surface changes and causes the transition of the condensation mode.

In order to achieve the dropwise condensation, aluminum substrates are irradiated with chromium ions and the steam condensation heat transfer performance on these surfaces was examined. Filmwise condensation was induced on the surface of aluminum specimens irradiated with chromium ion dose of less than 1016 ions/cm2 while dropwise condensation occurs on the specimens irradiated with chromium ion dose of 5×1016 ions/cm2 in the range of ion energy from 70 to 100 keV. The heat transfer coefficient of the surfaces on which dropwise condensation occurs appeared to be approximately twice as much as the prediction by Nusselt’s film theory. In a durability test, dropwise condensation lasts over six months and the heat transfer coefficient is also maintained.

Materials that can be manufactured with heat exchanger were selected to investigate chromium ions, and steam condensation was conducted using these materials. In experiments, as ion dose increased, dropwise condensation was implemented, but ion energies that could induce condensation tended to increase as the hardness of the material increased. The implemented liquid condensing heat transfer performance was 3.2 times higher for copper, 2 times for aluminum, 1.5 times for nickel, and more than 1.3 times for SUS304. These results show that the technique of dropwise condensation with chromium ion can be widely applied, although different materials can be applied depending on the type of working fluid and the operating environment.

However, condensation experiment was performed at approximately atmospheric pressure; thus, the phenomena needs examination at different pressure levels because numerous engineering systems are operated at different pressures, e.g. one twenty-fifth of atmospheric pressure for power plants.