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- Total number of questions : 20
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Agricultural Process Engineering [ Question No: 1 To 20 ] :
Which one of the following chemicals is NOT used for fumigation in either horizontal or vertical storage structures to kill insects?
Which of these is LEAST useful in assessing a project's viability?
Assertion (A): A pilot plant is built before committing to full scale.
Reason (R): Scale-up rarely behaves exactly as calculation predicts.
Select the correct answer from the options below.
An investment of \( 30 \) million returns a net cash inflow of \( 6.5 \) million a year. The simple payback period is
Fixed costs are \( 8.0 \) million a year, the selling price is \( 4200 \) per tonne and the variable cost is \( 2900 \) per tonne. The breakeven output is
Which of the following best explains why cleaning grain before storage is worthwhile?
Respiration of stored grain produces
A hopper outlet of \( 0.25 \) m diameter bridges with a damp material. Doubling the outlet diameter increases the outlet area by a factor of
Fuel of calorific value \( 42 \) MJ/kg is burnt at \( 14 \) kg per hour in a dryer evaporating \( 190 \) kg of water per hour. The specific energy consumption is
Air enters a dryer at a humidity ratio of \( 0.010 \) and leaves at \( 0.022 \) kg per kg dry air. To evaporate \( 60 \) kg of water the dry air required is
A drum dryer dries a liquid or slurry by
The wet bulb temperature of moist air is
A maize meal develops a rancid taste within a few weeks of milling.
Which processing step has most likely been omitted or done poorly?
Whitening in a rice mill removes
Assertion (A): A rasp-bar cylinder reduces the load on the cleaning shoe.
Reason (R): It breaks less straw into short pieces than a spike-tooth cylinder does.
Select the correct answer from the options below.
Grain carried out of the machine by the cleaning fan is known as _____ loss.
Which of these could NOT be removed by an air screen cleaner?
Statement I: A specific gravity separator works without any air flow.
Statement II: The deck oscillates to walk the separated fractions to their outlets.
In the light of the above statements, choose the correct answer.
Consider the following statements about viscoelastic behaviour in produce:
1. Stress relaxation is measured at constant strain.
2. Creep is measured at constant stress.
3. Bruising depends only on the magnitude of the load, not its duration.
Which of the statements given above is or are correct?
A grain bed of porosity \( 0.40 \) occupies \( 2.5 \) m\(^3\). The volume of air within it is
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20
Agricultural Process Engineering [ Question No: 1 To 20 ] :
Which one of the following chemicals is NOT used for fumigation in either horizontal or vertical storage structures to kill insects?
Your Answer : (Not Answered)
Correct 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.
Which of these is LEAST useful in assessing a project's viability?
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: The number of employees
Headcount says nothing about whether a project is worth doing - it is an input, and a large one may be a cost rather than a merit. Viability is judged by net present value, which discounts the whole cash flow, and supported by breakeven and payback, which measure the margin of safety and the exposure.
Assertion (A): A pilot plant is built before committing to full scale.
Reason (R): Scale-up rarely behaves exactly as calculation predicts.
Select the correct answer from the options below.
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: Both A and R are true, and R is the correct explanation of A
Because scale-up rarely behaves as calculated - heat transfer, mixing, handling and fouling all change with size - an intermediate step is worth its cost. The pilot plant is where those surprises are found cheaply, which is precisely why it is built.
An investment of \( 30 \) million returns a net cash inflow of \( 6.5 \) million a year. The simple payback period is
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: 4.6 years
\[ \text{Payback} = \frac{30}{6.5} = 4.6\ \text{years} \]Simple payback ignores what happens after that point and the time value of money, so it is a screening measure rather than a decision rule.
Fixed costs are \( 8.0 \) million a year, the selling price is \( 4200 \) per tonne and the variable cost is \( 2900 \) per tonne. The breakeven output is
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: 6154 tonnes
The contribution per tonne is \(4200 - 2900 = 1300\):
\[ Q_{BE} = \frac{8{,}000{,}000}{1300} = 6154\ \text{tonnes} \]Below this output the fixed costs are not covered; above it, every tonne adds 1300 to profit.
Which of the following best explains why cleaning grain before storage is worthwhile?
Your Answer : (Not Answered)
Correct Answer : D
Correct answer: Fines spoil first and impede airflow
Fines, dust, weed seeds and broken kernels are the most vulnerable material in the store: damaged and metabolically active, they carry a disproportionate share of the moisture, mould spores and insect eggs, and they spoil first, seeding trouble in the sound grain around them. They also pack into the spaces between whole kernels, raising the resistance to airflow and creating pockets aeration cannot reach.
Cleaning does not itself lower the moisture content of the sound grain, nor does it kill insects, and any change in bulk density is incidental.
Respiration of stored grain produces
Your Answer : (Not Answered)
Correct Answer : B
Living grain and the organisms in it burn dry matter, and all three products make matters worse: the heat and the water accelerate further respiration. A hot spot in a store is essentially this process running away with itself.
A hopper outlet of \( 0.25 \) m diameter bridges with a damp material. Doubling the outlet diameter increases the outlet area by a factor of
Your Answer : (Not Answered)
Correct Answer : D
Area goes as the square of diameter, so doubling gives four times the area. Enlarging the outlet is the most reliable cure for bridging, and it is why arching criteria are written in terms of a critical outlet dimension.
Fuel of calorific value \( 42 \) MJ/kg is burnt at \( 14 \) kg per hour in a dryer evaporating \( 190 \) kg of water per hour. The specific energy consumption is
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: 3.09 MJ per kg of water
The heat supplied per hour is the fuel rate times its calorific value, and the specific energy consumption divides that by the water evaporated:
\[ Q = 42 \times 14 = 588\ \mathrm{MJ/h} \]
\[ SEC = \frac{588}{190} = 3.09\ \mathrm{MJ\ per\ kg\ of\ water} \]
Against the latent heat of \( 2.3 \) MJ/kg this corresponds to an efficiency of about 74 per cent, which is good for a direct-fired dryer. The distractor \( 2.30 \) is the latent heat itself - the theoretical floor, not the actual consumption.
Air enters a dryer at a humidity ratio of \( 0.010 \) and leaves at \( 0.022 \) kg per kg dry air. To evaporate \( 60 \) kg of water the dry air required is
Your Answer : (Not Answered)
Correct Answer : D
Correct answer: 5000 kg
Each kilogram of dry air picks up the difference between the outlet and inlet humidity ratios:
\[ \Delta W = 0.022 - 0.010 = 0.012\ \mathrm{kg\ water\ per\ kg\ dry\ air} \]
\[ m_{air} = \frac{60}{0.012} = 5000\ \mathrm{kg\ dry\ air} \]
The distractor \( 2727 \) divides by the outlet humidity alone, ignoring the moisture the air already carried in. The calculation shows how large the air flow must be: five tonnes of air to remove sixty kilograms of water, which is why fan power is a significant part of a dryer's energy budget.
A drum dryer dries a liquid or slurry by
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: Spreading a film on a heated drum
A drum dryer applies a thin film of liquid or slurry to the surface of an internally steam-heated rotating drum. The film dries by conduction as the drum turns, and a doctor blade scrapes off the dried sheet, which is then broken into flakes or powder.
It suits pastes and slurries too viscous to atomise, and it is thermally efficient because heat passes directly into the film. Atomising into hot air describes a spray dryer, freezing and subliming describes a freeze dryer, and blowing air through a bed describes a fluidised or deep bed dryer.
The wet bulb temperature of moist air is
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: The steady temperature of a wetted thermometer
The wet bulb temperature is the steady reading of a thermometer whose bulb is covered by a wet wick with air moving over it. Evaporation from the wick removes latent heat until the cooling exactly balances the sensible heat arriving by convection, and the temperature settles at that equilibrium.
Because the evaporation rate depends on how far the air is from saturation, the wet bulb reading together with the dry bulb fixes the air's humidity - which is the whole basis of psychrometry. The dew point is a different temperature, reached by cooling rather than by evaporation.
A maize meal develops a rancid taste within a few weeks of milling.
Which processing step has most likely been omitted or done poorly?
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: Degermination before grinding
The maize germ is large, about ten to fourteen per cent of the kernel, and rich in oil that oxidises quickly once the kernel is broken open. If it is ground in with the endosperm the meal goes rancid within weeks. Degermination removes it before grinding, extending shelf life and yielding a valuable oil-bearing by-product at the same time.
Whitening in a rice mill removes
Your Answer : (Not Answered)
Correct Answer : D
Abrasive or friction whiteners scour the outer layers away, and the degree of whitening is expressed as the degree of milling. Over-milling costs both yield and nutrition while under-milling leaves a product that keeps badly.
Assertion (A): A rasp-bar cylinder reduces the load on the cleaning shoe.
Reason (R): It breaks less straw into short pieces than a spike-tooth cylinder does.
Select the correct answer from the options below.
Your Answer : (Not Answered)
Correct Answer : C
Correct answer: Both A and R are true, and R is the correct explanation of A
Both statements are true and the second explains the first. A rasp-bar works by rubbing the mat against the concave, whereas a spike-tooth strikes it; impact shatters straw and rubbing does not.
Short straw fragments pass through the concave with the grain and arrive at the cleaning shoe, where they must be sieved and blown out. Less broken straw therefore means a lighter load on the shoe and a cleaner sample for the same fan setting - a benefit realised two stations downstream of the cause.
Grain carried out of the machine by the cleaning fan is known as _____ loss.
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: blown
Blown loss is grain carried out of the machine by the cleaning fan along with the chaff. It is controlled by fan speed and by the sieve settings.
The adjustment pulls directly against sample cleanliness: a stronger blast removes more light material and gives a cleaner sample, but takes more grain with it. Setting the shoe means finding the balance between blown loss and purity, and measuring both rather than judging by eye.
Which of these could NOT be removed by an air screen cleaner?
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: Stones the same size as the grain
An air screen cleaner separates on size and on terminal velocity, and a grain-sized stone matches the grain in the first and exceeds it in the second, so neither the screens nor the aspiration will take it out. It needs a destoner, which works on density. The other three all differ from sound grain in size or in aerodynamic behaviour.
Statement I: A specific gravity separator works without any air flow.
Statement II: The deck oscillates to walk the separated fractions to their outlets.
In the light of the above statements, choose the correct answer.
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: Statement I is incorrect but Statement II is correct
Statement I is incorrect. A specific gravity separator depends absolutely on air flow: air is blown upward through the perforated deck to fluidise the bed, so that dense particles sink to the deck surface and light ones float above.
Statement II is correct and describes the other half of the mechanism. The deck oscillates to walk the settled heavy fraction uphill to its outlet while the fluidised light fraction flows downhill to another. Both actions are needed - air alone would stratify the bed without conveying it anywhere.
Consider the following statements about viscoelastic behaviour in produce:
1. Stress relaxation is measured at constant strain.
2. Creep is measured at constant stress.
3. Bruising depends only on the magnitude of the load, not its duration.
Which of the statements given above is or are correct?
Your Answer : (Not Answered)
Correct Answer : A
The first two are the standard definitions. Because part of the deformation is time-dependent, how long a load is held matters as much as how large it is, which is why stacking height and transit time both cause bruising.
A grain bed of porosity \( 0.40 \) occupies \( 2.5 \) m\(^3\). The volume of air within it is
Your Answer : (Not Answered)
Correct Answer : B
Porosity is the void fraction, so the air volume is \( 0.40 \times 2.5 = 1.0 \) m\(^3\). That air is both the path along which drying air travels and the reason a grain bed conducts heat so poorly that hot spots persist.
Marks
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20