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A biomimic surface was coated onto a poly(tetrafluoroethylene) (PTFE) substrate. The coated PTFE surface was found to have nanoscale roughness and high hydrophobicity. In the first preparation step, the PTFE surface was modified by plasma etching. A self-assembled monolayer (SAM) of octadecyltrichlorosilane (ODTS) was then deposited onto the modified surface with a thickness of a 2–3 nm. This surface was found to have self-cleaning features similar to those of a lotus leaf. The self-cleaning features were confirmed by comparing the contact and sliding angles of the original PTFE surface, a PTFE surface plasma treated, and a PTFE surface plasma treated and SAM coated. The PTFE surface treated with plasma and SAM coated had an increased contact angle and a decreased sliding angle compared with the other surfaces. It also exhibited increased stability and slow aging. The quantity of oxygen-containing groups that can be greatly influenced by plasma treatment, SAM coating, and aging, seems to play an important role in surface modification.

The three-dimensional flow structure inside an exhaust hood model of a low-pressure steam turbine was investigated using a particle image velocimetry (PIV) velocity field measurement technique. The PIV measurements were carried out in several selected planes under design operation conditions with simulated total pressure distribution and axial velocity profile. The mean flow fields revealed a complicated vortical flow structure and the major sources of energy loss. Vortices with different scales were observed inside the exhaust hood: a strong separation vortex (SV) behind the tip of the guide vane, a longitudinal vortex (LV) at the exhaust hood top, a large-scale passage vortex (PV) evolving throughout the flow path, and an end-wall vortex (EWV) in the region adjacent to the front end-wall. Both the SV and the large-scale PV seemed to consume large amounts of kinetic energy and reduce the pressure recovery ability. The results indicate that the steam guide vane and the bearing cone should be carefully designed so as to control the vortical flow structure inside the exhaust hood.

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