Q.1
Given below are two statements
Statement (I) : Hydrodynamic lubrication occurs when oil film is thick enough to prevent projections on one surface from
contacting those projections on the mating surface
Statement (II) : All bearings in an engine are in hydrodynamic lubrication when the engine is started from rest or when it is
coasting to a stop
In light of the above statements, choose the most appropriate answer from the options given below.
EXPLANATION
Ocean & Marine Renewable Energy: Ocean Thermal Energy Conversion (OTEC Carnot Limit) & Tidal Basin Power
- Regimes of Journal Bearing Lubrication:
- Statement (I): Hydrodynamic lubrication occurs when oil film is thick enough to prevent projections on one surface from contacting those projections on the mating surface. $\implies$ Correct.
- Hydrodynamic (full-film) lubrication separates mating asperities by creating a self-generating pressurized fluid wedge when the journal rotates at sufficient speed.
- Statement (II): All bearings in an engine are in hydrodynamic lubrication when the engine is started from rest or when it is coasting to a stop. $\implies$ Incorrect.
- At starting from rest and coasting to a stop, shaft rotational velocity is insufficient to develop hydrodynamic lift; bearings operate in the boundary or mixed lubrication regime, where metal-to-metal contact occurs.
- Conclusion: Statement (I) is correct but Statement (II) is incorrect (Option 3).
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