Mechanical Operations Questions

• In comminution theory, which empirical law states that the crushing energy is proportional to the new surface area created during size reduction?
• In industrial bag filters (fabric filters for dust collection), filter media are typically textiles or felts. Which of the following is never used as the filter fabric itself?
• For separating isotopes (extremely small mass differences), which centrifuge design is generally employed in practice?
• For separating abrasive solids suspended in a corrosive liquid stream, which filtration device is generally the most suitable choice (consider material compatibility and wear)?
• Which of the following ultrafine grinders primarily employ attrition (particle–particle and particle–wall friction) as the main mechanism for achieving micron/submicron sizes?
• Which grinding mill uses horizontally arranged rods as the grinding media and is known to deliver a more uniform granular product with minimal fines generation?
• Among the following minerals, which one has the minimum Rittinger’s number (i.e., requires the least energy per unit new surface area created) under comparable conditions?
• Mechanical conveyors that push material along a trough or through a tube are often called “scrapers.” Which of the following equipment types fall under this pushing/scraper category?
• State Rittinger’s crushing law in terms of energy–size reduction: which statement correctly represents its core idea?
• For a revolving (tumbling) mill, how does wet grinding compare with dry grinding in terms of practical operation and downstream handling/classification?
• Grizzlies (stationary bar screens) are used in screening operations primarily to separate which size class of solids before downstream crushing or screening?
• In the beneficiation of sulphide ores (e.g., copper, lead, zinc), which process has virtually no alternative for effective separation under most industrial conditions?
• Based on Mohs hardness, which of the following materials is the hardest: calcite, quartz, corundum, or gypsum?
• Grinding aids (surface-active additives) are primarily employed in which grinding mode to improve flowability, reduce agglomeration, and enhance mill throughput?
• Critical speed Nc (rpm) of a ball mill, in terms of mill radius R1 and ball radius R2 (both in metres), is correctly given by which expression?
• For mixing in the laminar regime (very low Reynolds number), how does the power number Po scale with the Reynolds number Re for a stirred tank (Po = P / (ρ N^3 D^5), Re = ρ N D^2 / μ)?
• In power requirement calculations for mixing in stirred tanks, which dimensionless group(s) are fundamentally important for correlating power number and operating regime?
• Regarding particle shape, what is the typical sphericity value for pulverised coal particles used in combustion systems?
• For a sphere falling where the drag coefficient is essentially constant (Newton’s regime, high Reynolds number), the terminal settling velocity varies with diameter d according to which proportionality?
• Cyclone separator design calculation: For a cyclone with body diameter 0.2 m and a measured tangential gas velocity of 15 m/s at the wall, estimate the dimensionless separation factor (also called the centrifugal acceleration ratio) using the standard relation based on local radius and gravity.