Steam condensate behavior and heat transfer performance on chromium-ion-implanted metal surfaces

Abstract

Aluminum, copper, nickel, and stainless steel 304 (SUS304) are widely used to construct heat exchangers. In this work, test specimens made of these metallic materials were irradiated with chromium ions. The static and dynamic contact angles of water droplets on the test specimens were measured to examine changes in the surface characteristics. Condensate behavior was visually observed and condensation heat transfer performance was experimentally measured. Filmwise condensation occurred on the surfaces of all the specimens that had no ion implantation. After these specimens were irradiated with chromium ions, filmwise condensation or dropwise condensation was induced depending on the ion irradiation conditions. When the substrates were irradiated with chromium ions at an ion energy level of 100 keV and an ion dose of 3 × 1016 ions/cm2, dropwise condensation occurred regardless of material. When the specimens were irradiated at an ion energy level of 70 keV, dropwise condensation, filmwise condensation, or both occurred depending on the substrate material. The condensation heat transfer coefficient of the surface where dropwise condensation occurred appeared to be more than 3.2 times larger than the theoretical value according to Nusselt’s film theory in the subcooling region below 9.5 K.