Biomimetic sealing system with hydrated materials for ocean current or tidal power generation

An all-new sealing system for a rotating shaft, which specializes in excellent separation between water and air, has been developed for installation in an ocean current or tidal power generator. Two seal lips made of a polyvinyl formal (PVF) were attached to a rotating shaft, and an aqueous solution of 3.0 wt% polyethylene glycol (PEG), a non-Newtonian fluid with a molecular weight of 2.0 million, was supplied between two lips for lubrication. Expected lubrication modes between the dynamic seal surfaces were hydration lubrication, soft-elastohydrodynamic lubrication, and weeping lubrication, similar to that observed in a natural synovial joint. Using PVF with a small porous diameter of 8 μm and continuously porous structure promoted hydration lubrication between seal surfaces at the molecular level, and low leakage of water, less than 0.05 ml/h, throughout the experiment. Mean frictional torque was lower than that found in the mechanical and oil seals that are generally used for industrial components. Frictional torque had been stable; the friction was independent of the shaft rotational speed, and the stick-slip friction that might lead to leakage of water was moderated in comparison with the conventional sealing systems.