Material Handling in Agro Industries Questions and Answers

Answer: C

Correct answer: They handle grain more gently than belt conveyors

This is the false statement, and it inverts the comparison. A screw drags material against a stationary trough, so attrition is far higher than on a belt, where the load rides along undisturbed. The other three are all true, and together they define where a screw belongs: short, enclosed, compact transfers where its penalties stay small.

Answer: D

Correct answer: Reducing the outlet size

Reducing the outlet makes bridging more likely, not less, since the critical arching dimension is exactly what the outlet must exceed. The other three all help: enlarging the outlet directly, steepening the walls to promote mass flow, and polishing them to reduce wall friction so material slides rather than keying against the surface.

Answer: A

Correct answer: The length of the run

Capacity depends on how much material the belt carries per metre and how fast it moves, so belt width, speed and bulk density all enter it while length does not. A long belt and a short one of the same section and speed deliver identical tonnages. Length governs the power instead, because friction accumulates along the run.

Answer: B

Correct answer: Unwise: power and breakage grow with length

A screw drags the material against the trough for the whole of its length, so both power and attrition rise in proportion to the run. Over 70 m the operating cost and product damage would swamp any saving in capital, and a belt would use a fraction of the power with almost no breakage.

Answer: C

Correct answer: Floor pressure approaches a limit with depth

This is the central result of Janssen’s analysis. Because wall friction carries an increasing share of the weight as depth increases, the vertical pressure on the floor approaches an asymptote instead of rising in proportion to depth as it would in a liquid. That is why a tall grain bin does not need a floor designed for the full head of material.

Answer: D

Correct answer: Adding an extra elevator

Every transfer adds breakage, so an extra elevator adds two more transfers and makes matters worse. The other three all reduce damage, and they are the three standard measures: lower drop heights, belts rather than screws, and lifting once to the top before distributing by gravity so that nothing is raised twice.

Answer: A

Correct answer: They prevent an explosion from occurring

Relief panels are a mitigation, not a prevention. They open at a set pressure so that the burning gases escape before the pressure can reach the strength of the casing, and they are oriented so that the blast goes somewhere safe. Prevention is the business of dust extraction and ignition control, and the two are used together.

Answer: B

Correct answer: The colour of the material

Colour has no bearing on how a material should be moved. Fragility decides whether a gentle conveyor is needed, bulk density converts volume into tonnage and hence sets capacity, and the angle of repose governs the surcharge profile on a belt and the slope a chute must have. All three are on the standard selection checklist.

Answer: C

Correct answer: It moves material slowly and damages it less

Dense phase pushes material along as plugs or dunes at low velocity rather than keeping it suspended. Since impact damage at bends grows with the square of velocity, the low speed makes it much the gentler of the two pneumatic methods, and it uses less air. The price is a higher pressure requirement and more complex equipment.

Answer: D

Correct answer: Wall friction carries much of the weight

A liquid transmits pressure hydrostatically, so the floor pressure would grow in proportion to the depth. Grain does not: friction between the grain and the wall carries an increasing share of the weight as depth increases, so the vertical pressure approaches a limit. Janssen’s analysis accounts for that friction, which is the whole difference between the two models.