An experimental investigation into the effect of Cu2O particle size on antifouling roughness and hydrodynamic characteristics by using a turbulent flow channel

Copper and copper compounds are commonly used as biocides against biofouling on surfaces exposed to seawater. Copper oxide, one of the most commonly used forms of copper biocide, can provide an efficient mechanism for fouling-free surfaces, resulting in substantial fuel savings and reduction of Greenhouse Gases (GHG) emissions. However, copper oxide is commercially formulated with different particle sizes, which can consequently lead to surfaces with different roughness conditions. The roughness effect of various sizes of copper oxide particles on the drag performance of antifouling coatings, and hence on the ship hull drag, has not been systematically studied in the past. Therefore, to investigate the effect of particle sizes on antifouling roughness and hydrodynamic characteristics, a number of different sized cuprous oxide pigments (with median size ranging from 2  μm to 250 μm) were applied on Newcastle University's (UNEW) standard acrylic flat test panels. Roughness characteristics were analysed by using an optical surface profilometer. Moreover, the microstructure observations of all test specimens were carried out using Scanning Electron Microscopy (SEM). Subsequently, a laboratory experiment of streamwise pressure drop measurements was conducted on all coated plates and compared to uncoated acrylic control panels. The Reynolds number for the experiment, based on bulk mean velocity and channel height, ranged from 3×104 to 1.6×105. Analysis indicated that for the panels coated with particle sizes ≥12μm, the roughness characteristics and frictional drag increased as particle size increased. Interestingly, due to particle agglomeration and surface finish condition, those panels coated with particle sizes <12μm were found not to follow this trend and had higher roughness and drag characteristics than expected.