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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

ATTEMPTS TO REALIZE LONG-LASTING DROP-WISE CONDENSATION OF STEAM ON METALLIC SURFACES

Get access (open in a dialog) DOI: 10.1615/IHTC16.kn.000006
pages 139-148

Abstract

Numerous thermal-energy systems incorporate condensers to reject heat. The condensation can be classified into three modes depending on the condensate flow behavior: film condensation (FWC), dropwise condensation (DWC), and conventional condensation. The condensation heat transfer performance of the DWC is superior to the other modes because the condensate does not wet the surface so that thermal resistance is minimized. That is why the DWC has been of interest to heat transfer researchers. Previous experiments demonstrated that a hydrophobic textured surface may be changed into a hydrophilic surface when water vapor condenses on the surface. The condensate nucleated to the bottom and the pillar side walls appeared to be sticky and would not climb up the pillar to form a spherical droplet. In order to avoid this pinning effect, ions implantation for flat metallic substrates was examined. Argon, Nitrogen, and Chromium ions are accelerated and irradiated onto metallic substrates. This method allows surface modification without fabrication of micro/nano-size texture and polymer coatings. Physical and chemical interaction is expected to occur in thin layer near the substrate surface when the high energy ions are irradiated. The effects of ion-irradiation on aluminum and copper substrates were experimentally observed in terms of a change in contact angle, surface morphology, and steam condensation heat transfer coefficient. The results show that the DWC occurs on a Cr-ion implanted aluminum and the DWC lasts for more than six months. Condensation heat transfer coefficient appeared to be two-fold larger than that predicted by Nusselt theory.