Question 5 QMED01 - Junior Engineer

The Correct Answer is B **Why option B ("high temperature and a low viscosity") is correct:** Oil cleaning and filtration (whether by centrifuge or simple filtration) rely on separating suspended contaminants (solids, water, etc.) from the base oil. The ease and effectiveness of this separation process are primarily determined by the oil's viscosity. 1. **High Temperature:** Increasing the temperature of the oil significantly lowers its viscosity. Lowering the viscosity allows contaminants to move more freely within the oil, reducing resistance to flow through filters or allowing denser particles (like solids) and water droplets to settle out much faster under gravity or centrifugal force (Stokes' Law). 2. **Low Viscosity:** A lower viscosity means the oil is thinner, enabling faster filtration rates and higher separation efficiency in centrifuges. The contaminants are less likely to be trapped or held in suspension by the viscous forces of the oil, leading to the most effective cleaning. **Why the other options are incorrect:** * **A) high temperature and a high viscosity:** This option is contradictory. High temperatures drastically reduce the viscosity of typical lubricating oils. If an oil somehow maintained a high viscosity at a high temperature, the effectiveness of filtration/centrifugation would be severely hindered due to the high resistance to flow and separation forces. * **C) low temperature and a high viscosity:** Low temperatures naturally result in high viscosity. High viscosity makes the oil thick, significantly slowing down the filtration process and severely impeding the settling velocity of contaminants in a centrifuge, making cleaning highly inefficient and potentially damaging filters. * **D) low temperature and a low viscosity:** Low temperatures inherently lead to high viscosity in most oils. If a very low-viscosity oil were used, cooling it down would still increase its viscosity, slowing down the process compared to heating it up (Option B). Therefore, low temperature is counterproductive to achieving the *most* effective cleaning.