Sustaining dropwise condensation on nickel-plated copper surfaces with As-grown graphene coatings

Abstract

• Dropwise condensation on as-grown graphene on electroplated Ni has been achieved. • Dropwise condensation has been successfully promoted on Cu using Ni-Gr coatings. • Condensation rate has been enhanced up to 2.9 times higher than filmwise mode. • The electroplated Ni-Gr coatings on Cu are more robust than the Ni-Gr surface. Dropwise condensation (DWC) has been extensively investigated owing to its substantially higher efficiency compared with filmwise condensation (FWC). However, performing the highly efficient DWC has been hindered by the durability of existing hydrophobic surface coatings. Graphene grown on Nickel (Ni-Gr composite) has been demonstrated in our previous study to sustain the DWC in an aggressive condition for more than 36 months. Compared with traditional heat exchangers made of copper (Cu) and stainless steel, the high purity requirement of Ni substrate for graphene growth and high material cost greatly limit its practical applications. In this study, the cost-effective nickel-plating technique has been explored to apply the robust Ni-Gr coating on prevail metals such as Cu in industry. DWC can be sustained for more than 180 days without noticeable degradation in a steam/air mixture environment. After 180 days, the Ni-Gr coating electroplated on the copper surface (Cu-Ni-Gr) can still facilitate DWC with approximately 2.9 times higher condensation heat transfer rate than that of conventional metal surfaces. The consistently superior anticorrosion properties of Cu-Ni-Gr surfaces is further revealed by Tafel tests. An additional 46% lower corrosion rate than the Ni-Gr surface has been characterized. This study manifests a feasibility to implement the sustainable and highly efficient DWC on other popular heat exchanging metals using super-durable Ni-Gr coatings.