Storage Engineering Questions and Answers

Answer: C

Correct answer: The three continuous loads

Once the produce is at temperature the product pull-down load ceases entirely - it is a transient, present only while the produce is being cooled. What remains is respiration at \( 1.8 \) kW, transmission at \( 1.4 \) kW and infiltration at \( 2.6 \) kW, a continuous total of about \( 5.8 \) kW.

The table therefore describes two quite different duties: a peak of \( 42.8 \) kW during pull-down and a holding load of \( 5.8 \) kW thereafter. Sizing on the holding load alone would leave the plant unable to pull down; sizing on the peak alone leaves it cycling inefficiently for most of its life.

Answer: D

Correct answer: Hold the bulk below about 15 degrees

The table shows development ceasing entirely at 15 degrees, while at 20 degrees the generation time is still 60 days and at 27 it has fallen to 28. Only the 15 degree line stops the population from growing at all, so that is the aeration target.

Twenty degrees would slow the insects but not stop them - over a six-month storage season that is still three generations. This is why aeration is run whenever ambient air is cool enough to advance the front, typically at night or through the cooler months.

Answer: A

Moving from four to one and a half per cent loss saves twenty-five kilograms a tonne, which comfortably repays the aeration plant. The further step to controlled atmosphere costs far more than the one per cent it saves on a commodity.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Oil holds essentially no water, so in an oilseed the moisture is confined to the smaller non-oil fraction. Since moisture content is quoted on the whole-seed basis, the seed reaches any given equilibrium relative humidity at a much lower stated moisture than a cereal would.

Because mould growth is governed by that equilibrium relative humidity - above about 70 per cent - the safe moisture for groundnut is around 7 per cent against 13 to 14 for cereals. The threshold is the same; only the moisture content corresponding to it differs.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Storage insects breed rapidly between about 25 and 33 degrees and their development effectively stops below about 15, so bringing the bulk below that temperature arrests the population.

Aeration is therefore an insect control measure in its own right, not merely a way of managing moisture gradients - and an attractive one, since it leaves no residue, cannot select for resistance, and simultaneously slows mould growth and respiration. Its limitation is that it depends on ambient air being cool enough to be useful.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Carbon dioxide from a developing spoilage focus diffuses through the interstitial air and reaches sampling points anywhere in the bulk, whereas the heat generated alongside it stays local, because grain conducts heat poorly and the air moves slowly.

A temperature probe therefore responds only if it happens to lie within or very near the spot, while the gas reading responds wherever the sample is drawn. This is why a steadily rising carbon dioxide level with normal probe readings should be taken seriously rather than dismissed.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. In hermetic storage nothing is added: the grain, insects and moulds respire, depleting the oxygen and raising the carbon dioxide until the atmosphere itself becomes lethal to the infestation.

Since the protection comes entirely from the atmosphere the biology creates, no chemical is applied and none can remain - which matters where residue limits are tight, where organic certification is sought, or where phosphine resistance has already developed. The requirement is simply that the seal holds.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Moisture migration is driven by temperature gradients within the bulk, which set up slow convection currents in the interstitial air. Concrete's thermal mass damps the daily and seasonal swings, so those gradients are smaller and the circulation weaker.

A thin steel wall, by contrast, follows the ambient temperature closely, so the grain near the wall swings while the core lags - the largest gradients, and the strongest driving force. Metal silos are cheap and quick to erect, which is why they remain common despite needing more careful aeration.

Answer: C

Correct answer: A is false but R is true

The assertion is false. Fumigation is no substitute for hygiene and sealing - it is a corrective treatment that depends on both.

The reason is true and explains why: a lethal gas concentration must be maintained throughout the exposure period, which for phosphine means several days, and only a well-sealed structure can hold it. A leaky store gives a sublethal exposure that kills the susceptible insects and selects for the resistant ones. Residues in cracks and spillage reinfest the grain as soon as the gas clears, so hygiene determines how soon fumigation is needed again.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both statements are true and the reason explains the assertion. Because respiration roughly doubles for every ten degree rise, produce at 30 degrees is metabolising perhaps four times as fast as it will at 10 - consuming its reserves, losing water and ripening at that accelerated rate from the moment it is picked.

The first hours therefore account for a disproportionate share of the storage life used up, and none of it can be recovered by cooling later. This is why cooling capacity is placed at the packhouse rather than only at the store.