ICAR AICE-JRF/SRF (PhD) — Agricultural Engineering subjects 38–43 · India · National Testing Agency for ICAR
Original practice questions written to the published syllabus · not past papersMoisture, drying, parboiling, milling, cleaning, size reduction and conveying of grains, pulses and oilseeds.
In the exams: GATE AG Section 6 (~14 marks a year 2019–26; psychrometry in all 8 papers, rice milling in 6 of 8); ICAR AIEEA-PG Unit VI; ICAR AICE subject 41; NCEES PE processing; PRC ABE bioprocess; ASRB NET ASPE
ICAR AICE-JRF/SRF (PhD) — Processing and Food Engineering (subject 41)
Units on post-harvest unit operations, process technology and machinery and design of processing machinery ask for PG depth: sorption models (GAB, BET, modified Henderson), thin-layer and diffusion models and effective diffusivity, deep-bed models, dryer design and performance indices, parboiling kinetics and quality, extraction and refining steps, and design relations for conveyors and mills.
How our questions for ICAR AICE-JRF/SRF spread across the units of Post-Harvest Engineering of Cereals, Pulses & Oilseeds. Difficulty: 1 easy, 20 medium, 19 hard.
| Thin-layer drying models | 7 | |
| Equilibrium moisture content and sorption isotherms | 6 | |
| Size reduction: Rittinger, Kick and Bond laws | 5 | |
| Drying theory: constant and falling rate periods | 4 | |
| Oil expression and solvent extraction | 4 | |
| Psychrometry and properties of air | 2 | |
| Cleaning, grading and screening effectiveness | 2 | |
| Conveying: belt, bucket, screw and pneumatic | 2 | |
| Seed processing | 2 | |
| Moisture content: wet and dry basis | 1 | |
| Grain dryers: bin, LSU, recirculating, fluidised-bed and solar | 1 | |
| Parboiling and hydrothermal treatment | 1 | |
| Paddy and rice milling: husking, whitening, polishing and yields | 1 | |
| Wheat milling | 1 | |
| Pulse milling | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
One tonne of maize at 30% moisture (dry basis) is dried to 12% moisture (wet basis). The water removed is closest to
D. 126 kg
Dry matter = 1000/(1 + 0.30) = 769.2 kg. Final mass at 12% wb = 769.2/0.88 = 874.1 kg. Water removed = 1000 − 874.1 = 125.9 kg. 180 kg subtracts percentages on mixed bases; 231 kg is the total water initially present, as if dried to zero moisture. 205 kg treats the initial 30% as wet basis.
Further reading: Chakraverty, Post Harvest Technology of Cereals, Pulses and Oilseeds
A tray holds 50 kg of dry solid on 2 m² and dries at a constant rate R_c = 1.5 kg/m²·h down to the critical moisture X_c = 0.6 (db); the rate then falls linearly to zero at X_e = 0.05. The falling-rate time from 0.6 to 0.15 kg/kg (db) is closest to
A. 15.6 h
t_f = [W_s(X_c − X_e)/(A R_c)] ln[(X_c − X_e)/(X − X_e)] = (50 × 0.55/3) × ln(0.55/0.10) = 9.167 × 1.7047 = 15.63 h. Dropping the log term gives 9.2 h; using total rather than free moisture in the log gives 12.7 h; 25.6 h is the total including the constant-rate period.
Further reading: Earle, Unit Operations in Food Processing
Treating a grain kernel as a sphere of radius 2 mm, the late-period plot of ln MR against time (s) has a slope of −1.2 × 10⁻⁴ s⁻¹. The effective moisture diffusivity is closest to
C. 4.86e-11 m²/s
First term of the sphere solution: ln MR = ln(6/π²) − (π²D/r²)t, so D = |slope|·r²/π² = 1.2 × 10⁻⁴ × (2 × 10⁻³)²/9.8696 = 4.86e-11 m²/s, within the usual 10⁻¹¹–10⁻¹⁰ range for grains. Omitting π² gives 4.80e-10; using the diameter instead of the radius gives a value four times too large.
Further reading: Brooker, Bakker-Arkema and Hall, Drying and Storage of Grains and Oilseeds
Effective diffusivity of paddy is 3.0 × 10⁻¹¹ m²/s at 40 °C and 6.0 × 10⁻¹¹ m²/s at 60 °C. The Arrhenius activation energy is closest to
D. 30.1 kJ/mol
E_a = R ln(D₂/D₁)/(1/T₁ − 1/T₂) = 8.314 × 0.6931/(1/313.15 − 1/333.15) = 8.314 × 0.6931/1.9171e-04 = 30061 J/mol ≈ 30.1 kJ/mol. Using Celsius temperatures gives a nonsense small value; multiplying by 2.303 treats the natural log as a common log. 13.1 kJ/mol uses log₁₀ 2 instead of ln 2; 0.692 kJ/mol is the Celsius result; 69.2 kJ/mol multiplies by 2.303.
Further reading: Brooker, Bakker-Arkema and Hall, Drying and Storage of Grains and Oilseeds
In the Page thin-layer model MR = exp(−k tⁿ), the exponent n
A. is an empirical shape parameter letting the curve depart from a simple exponential
Page added n to Lewis's exponential to improve fit; n = 1 reduces it to the Lewis model. It has no direct physical meaning, unlike k, which follows Arrhenius behaviour.
Further reading: Brooker, Bakker-Arkema and Hall, Drying and Storage of Grains and Oilseeds
Smooth crushing rolls of 500 mm diameter are set with a 10 mm gap and fed 30 mm particles. The minimum coefficient of friction needed for the particles to be nipped is closest to
A. 0.283
cos b = (R + d)/(R + r) = (250 + 5)/(250 + 15) = 0.9623, so the half nip angle b = 15.79°, and μ ≥ tan b = 0.283. Using the full nip angle gives 0.615; using the full gap instead of half the gap gives 0.197. 0.272 is sin b instead of tan b.
Further reading: McCabe, Smith and Harriott, Unit Operations of Chemical Engineering
Ground feed has a fineness modulus of 3.0. Using the Henderson–Perry relation D = 0.104 × 2^FM, the average particle size is closest to
D. 0.83 mm
D = 0.104 × 2³ = 0.832 mm. 0.0041 × 2^FM gives inches (0.0328 in), not millimetres; the other options misapply the exponent. 0.62 mm multiplies 2 by FM instead of raising it (0.104 × 6); 0.94 mm squares FM (0.104 × 3²).
Further reading: Henderson and Perry, Agricultural Process Engineering
A screw conveyor has a 0.30 m flight diameter, 0.06 m shaft, 0.30 m pitch, runs at 60 rpm with a loading factor of 0.30, and handles grain of 750 kg/m³. Its capacity is closest to
A. 16.5 t/h
Q = (π/4)(D² − d²)·p·N·ρ·φ = 0.7854 × (0.09 − 0.0036) × 0.30 × 60 × 750 × 0.30 = 274.8 kg/min = 16.5 t/h. Ignoring the shaft gives 17.2 t/h; ignoring the loading factor gives 55.0 t/h (a full trough). 0.27 t/h is the 274.8 kg/min read as t/min and mislabelled.
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
In horizontal dilute-phase pneumatic conveying of grain, if the air velocity falls below the saltation velocity,
C. particles drop out of suspension and form deposits or dunes in the pipe
Saltation velocity is the minimum horizontal velocity to keep particles suspended; below it they settle and can block the line. The vertical equivalent is the choking velocity.
Further reading: McCabe, Smith and Harriott, Unit Operations of Chemical Engineering
By Harrington's rules of thumb, lowering seed moisture by 2 percentage points and storage temperature by 10 °C would multiply expected storage life by roughly
A. 16
Moisture: 2 × 2 = 4; temperature: each 5 °C fall doubles life, so 10 °C gives 4; combined 4 × 4 = 16. Adding the factors (4 + 4 = 8) is the common slip. 6 adds the moisture factor to a single temperature doubling (4 + 2).
Further reading: Harrington's rules for seed storage
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