Impact of Surface Roughness and Coning on Hydrodynamic Face Seals During an Idling Process of Main Coolant Pump in Mixed Lubrication Regime

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Abstract The hydrodynamic face seal of the main coolant pump (MCP) of a nuclear power plant operates under hydrodynamic lubrication. At low idle speed, the seal faces may touch, transitioning the lubrication regime from hydrodynamic to mixed. A new equation for the film thickness on the coning face with a wavy-tilt-dam (WTD) is developed, applying the average Reynolds equation with the Jacobson–Floberg–Olsson (JFO) boundary and using a statistical asperity contact model. Surface roughness and coning influence the minimum film thickness, load-carrying capacity, and friction coefficient, determining the shift from mixed to hydrodynamic lubrication. Under ΔP = 0.8 MPa and 20 r/min, the no-coning WTD face seal remains noncontact at σ = 0.1 μm, while it makes contact at σ = 0.56, 0.35, and 0.28 μm. The WTD face seals with fconing = 1.0 μm at all σ are in contact. Smoother surfaces reduce the summit contact probability, promoting the seal face to lift off. Coning decreases the hydrodynamic effect, leading to lower hmin and a higher chance of rough summit contact. A test rig is built, and the idling process is simulated 50 times, revealing a contact wear pattern at σ = 0.1 μm with fconing = 1.0 μm, while no wear pattern is observed with low coning. The 0–0.3 μm coning value and σ = 0.1 μm are appropriate for WTD face seals under mixed lubrication. This research provides a basis for the stable operation of hydrodynamic WTD face seals in MCP.

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