Question 53 3AE01 - Third Assistant Engineer

The Correct Answer is B **Explanation for Option B (high temperature and a low viscosity):** Oil cleaning and filtration (whether using a filter medium or centrifugation) rely on efficiently separating contaminants (like dirt, metal particles, or water) from the base oil. The primary factor governing the speed and effectiveness of this separation is the oil's viscosity. * **Viscosity and Flow:** A lower viscosity means the oil flows more easily and quickly through filters, allowing for smaller micron ratings to be used without excessively slowing down the process. * **Viscosity and Separation (Centrifuge):** In a centrifuge, low viscosity allows suspended solid contaminants and denser liquids (like water) to migrate more quickly to the outer wall under centrifugal force, leading to highly efficient separation. * **Temperature and Viscosity Relationship:** For lubricating oils, viscosity is inversely proportional to temperature. Heating the oil significantly lowers its viscosity. Therefore, operating the filtration or cleaning system at a **high temperature** ensures the **lowest possible viscosity** (within safe operating limits), maximizing the efficiency and speed of the cleaning process. **Why the other options are incorrect:** * **A) high temperature and a high viscosity:** This option is physically contradictory for standard lubricating oils. High temperatures inherently reduce viscosity, not increase it. If an oil *did* maintain high viscosity at high temperatures, cleaning effectiveness would suffer due to poor flow and poor separation. * **C) low temperature and a high viscosity:** Low temperatures cause the oil to become thick (high viscosity). High viscosity drastically impedes both standard filtration (clogging filters quickly, slowing flow) and centrifugation (preventing contaminants from settling efficiently), resulting in the least effective cleaning scenario. * **D) low temperature and a low viscosity:** Similar to Option A, this is contradictory for most oils. Low temperatures typically result in high viscosity. Even if an oil retained a low viscosity at low temperatures, the main goal of heating is to *reduce* viscosity further and often to aid in removing dissolved water (which is easier at high temperatures). Low temperature does not optimize the cleaning process.