Material Handling in Agro Industries Questions and Answers

Answer: A

Correct answer: Air velocity has fallen below saltation

Saltation velocity is the minimum at which particles stay suspended. Below it they settle on the bottom of the pipe, the effective area falls, the velocity drops further, and the line blocks - a runaway once it starts. The remedy is to restore the velocity, which usually means checking for a leak, a worn blower or an increase in solids loading.

Answer: B

Correct answer: It limited the pressure rise and directed the blast

Relief panels do not prevent an explosion; they open at a set pressure so that the burning gases vent to a safe direction before the pressure inside can reach the strength of the casing. The structure survives and the blast goes where it does least harm. Prevention is a separate line of defence, chiefly dust extraction and ignition control.

Answer: C

Correct answer: The belt, for lower power and less damage

Over 90 m a screw drags the grain against a stationary trough for the whole distance, which costs both power and breakage, and both grow with length. A belt carries the grain rather than dragging it, so the power is a fraction and the damage almost nil. A screw earns its place on short enclosed transfers, not on long runs.

Answer: D

Correct answer: bridging

Bridging, or arching, is the formation of a stable arch of material across the hopper outlet, held up by the cohesion between particles and by friction at the walls. Flow stops even though the outlet is open. It is a property of cohesive materials - damp grain, flour, meal - and it is cured chiefly by enlarging the outlet beyond the critical arching dimension.

Answer: A

Correct answer: ratholing

A rathole is a stable vertical channel that empties above the outlet while the material around it stands still, held up by its own cohesion. It is a funnel flow phenomenon: the stagnant material stays in place indefinitely, which matters where the product can spoil or where the bin’s working capacity has effectively been lost.

Answer: B

Correct answer: mass

In mass flow every particle is in motion whenever anything is withdrawn, so there are no stagnant regions and the bin discharges first-in first-out. It requires steep smooth walls and an adequate outlet. The alternative, funnel flow, moves only a central core and leaves the rest in place - the condition in which ratholing occurs.

Answer: C

Correct answer: boot

The boot is the bottom section, where the buckets pass through the accumulated material and scoop it up. Its design governs how gently the grain is picked up and how completely; too little material and the buckets fill poorly, too much and they dig, which costs power and breaks grain. The head is the top section, where the buckets discharge.

Answer: D

Correct answer: saltation

Saltation velocity is the minimum gas velocity at which particles remain entrained in a horizontal line. Below it they fall out and settle along the bottom of the pipe, which reduces the flow area and can lead to a complete blockage. Dilute phase conveying must therefore run above it with a margin, which is why it is a high-velocity and high-power method.

Answer: A

Correct answer: Drag conveyor

Enclosure rules out the belt, which is the only one of the four that is open. Among the three enclosed options the drag conveyor has both the lowest power at 11 kW and much the lowest breakage at 0.15 per cent, against 0.60 for the screw and 0.90 for pneumatic. It is the obvious choice once enclosure is a requirement.

Answer: B

Correct answer: Bucket elevator

The geometry decides it. Raising 15 m within a 4 m footprint needs an inclination of about 75 degrees, and only the bucket elevator, which works vertically, can do it. A screw at 45 degrees would need 15 m of horizontal run, a cleated belt at 35 degrees over 21 m, and a plain belt at 20 degrees over 41 m - all far beyond the space available.