Storage Engineering Questions and Answers

Answer: D

The chemical NOT used as a fumigant is silver sulphate.

A fumigant must be a gas, or release one, that penetrates bulk grain and kills insects. Methyl bromide is such a gas, and aluminium phosphide formulations, sold as Phostoxin, release phosphine gas on contact with moisture.

Silver sulphate is a stable solid salt that releases no toxic vapour, so it has no role in fumigating storage structures.

Answer: A

The equivalent diameter is 4 m.

The hydraulic radius of a bin cross-section is its area divided by its perimeter. For a circle of diameter \(D\):

\[ \begin{aligned} R &= \frac{\pi D^{2}/4}{\pi D} = \frac{D}{4} \\ D &= 4R = 4 \times 1 = 4\ \text{m} \end{aligned} \]

The height, bulk density and friction coefficient are what Janssen's equation needs for wall pressures, but they play no part in this geometric step. 1 m is the hydraulic radius itself, 2 m treats the hydraulic radius as the radius, and 8 m is the height of the bin.

Answer: D

The recommended safe storage moisture is 10-12%.

Stored cereals stay sound only while their moisture is low enough to stop moulds, to keep insect and mite activity low and to keep respiration slow. Indian grain storage guidance recommends drying cereals to about 10 to 12 percent moisture (wet basis) for storage over six to twelve months, and in warm humid tropical conditions a one-year store needs the grain at the lower end of the safe range. FAO guidance on cereals sets the ceiling a little higher, at about 12 to 13 percent, so the keyed range is the cautious end of what is accepted.

13-15% is above the safe level: grain at 14 to 15 percent starts to heat and mould in a warm store. 6-7% and 8-9% are drier than is needed for cereals; they are more typical of oilseeds and pulses held for long periods, and drying cereals that far wastes energy and weight without benefit.

Answer: A

The key gives the range 16 to -2 °C.

Cold storages for perishable produce operate above freezing, or just below it, at temperatures chosen for each commodity: around -1 to 2 degrees for apples, grapes and many leafy vegetables, about 2 to 4 degrees for potatoes, and up to about 10 to 15 degrees for chilling-sensitive produce such as bananas, mangoes and tomatoes. Taken together, perishables are stored between roughly -2 and 16 degrees C.

The ranges 17 to 16 and 20 to 18 degrees are too warm and narrow to cover the commodities stored, and -3 to -5 degrees would freeze and damage fresh fruits and vegetables; that belongs to frozen storage.