Drag reduction in ultrahydrophobic channels with micro-nano structured surfaces

A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces. However, in previous experiments, the ultrahydrophobic surfaces were fabricated with micro-structures or nano-structures and the channels were on the microscale. For the drag reduction in macro-scale channels few reports are available. Here a new method was developed to fabricate ultrahydrophobic surfaces with micro-nano hierarchical structures made from carbon nanotubes. The drag reductions up to 36.3% were observed in the macro-channels with ultrahydrophobic surfaces. The micro-PIV was used to measure the flow velocity in channels. Compared with the traditional no-slip theory at walls, a significant slip velocity was observed on the ultrahydrophobic surfaces.