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 papersStoring grain and produce safely, the loads it puts on bins and silos, and the conveyors and packages that move and protect it.
In the exams: GATE AG Section 6 (bin/silo pressure in 6 of 8 papers 2019–26); ICAR AICE subject 41 Units 6–7; NCEES PE (ANSI/ASAE S433 supplied); ASRB NET ASPE
ICAR AICE-JRF/SRF (PhD) — Processing and Food Engineering (subject 41)
Unit 6 (material handling, packaging and transport) and Unit 7 (storage engineering) at PG depth: derivation and assumptions of Janssen's equation, Airy's wedge analysis, flow patterns and Jenike design, moisture migration, airflow resistance and fan selection, fumigation CT and resistance, CA/MA equilibrium, permeation theory, shelf-life models and packaging machinery.
How our questions for ICAR AICE-JRF/SRF spread across the units of Storage Engineering, Material Handling & Packaging. Difficulty: 2 easy, 40 medium, 27 hard.
| Janssen's and Airy's theories of bin pressure | 9 | |
| Aeration of stored grain | 8 | |
| Fumigation | 8 | |
| Controlled and modified atmosphere storage | 8 | |
| Barrier properties of packages | 8 | |
| Causes of storage losses | 6 | |
| Packaging materials: paper, plastics and laminates | 6 | |
| Bins and silos | 5 | |
| Packaging machines | 5 | |
| Design of conveyors and elevators | 5 | |
| Bag and bulk storage | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In a 6 m diameter bin (μ′ = 0.4, k = 0.4), at roughly what depth does the Janssen pressure reach 95% of its limiting value?
C. 28.1 m
1 − e^−x = 0.95 when x = 3 (e^−3 = 0.050). So μ′kh/R = 3 → h = 3R/(μ′k) = 3 × 1.5/(0.4 × 0.4) = 28.1 m. At h = R/(μ′k) = 9.4 m the pressure is only 63% of the limit; using the bin radius (3 m) instead of the hydraulic radius R = D/4 = 1.5 m gives 56.2 m. 11.2 m omits k (3 × 1.5/0.4).
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
A square bin of 5 m side holds grain of specific weight 7.6 kN/m³. With k = 0.45 and μ′ = 0.35, what is the Janssen vertical pressure at 12 m depth?
D. 47.0 kPa
R for a square = side/4 = 1.25 m. μ′kh/R = 0.35 × 0.45 × 12/1.25 = 1.5120. V = (γR/μ′k)(1 − e^−x) = (60.317)(1 − 0.2205) = 47.0 kPa. γh = 91.2 kPa ignores wall friction; using R = side/2 gives 64.0 kPa; kV = 21.2 kPa is the lateral pressure.
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
Why do grain-bin design standards apply overpressure factors to static Janssen pressures?
B. Pressures during discharge, eccentric flow and thermal or moisture effects can exceed static fill pressures
Measured wall pressures during emptying (and with eccentric flow, swelling or wall contraction in cold weather) can exceed the static Janssen values, so standards multiply them by factors. The factors increase, not reduce, design loads.
A 3 g tablet contains 56% aluminium phosphide (AlP, 57.95 g/mol). How much phosphine (PH3, 34.00 g/mol) can it release?
C. 0.99 g
AlP = 3 × 0.56 = 1.68 g = 0.0290 mol; 1 mol AlP gives 1 mol PH3, so PH3 = 0.0290 × 34.00 = 0.99 g (about 1 g). 1.68 g is the mass of AlP, not PH3; 1.76 g ignores the 56% content; inverting the molar mass ratio gives 2.86 g.
Further reading: FAO Manual of fumigation for insect control
A fumigation label concentration is given as 1 g/m³ of phosphine. What is this in ppm (v/v) at 25 °C?
B. 719 ppm
ppm = (mg/m³) × Vm/M = 1000 × 24.45/34.0 = 719 ppm. Using 22.41 L/mol gives 659; treating mg/m³ as ppm gives 1,000; inverting gives 1,391.
Further reading: FAO Manual of fumigation for insect control
A 1 kg pack of produce respires 10 mL O2 kg⁻¹ h⁻¹ at storage temperature. The film has an oxygen transmission rate of 5000 cm³ m⁻² day⁻¹ atm⁻¹. What film area gives a steady-state internal O2 of 5% (outside 21%, total pressure 1 atm)?
D. 0.300 m²
O2 consumed = 10 × 1 × 24 = 240 mL/day. At steady state this equals OTR × A × ΔpO2 = 5000 × A × (0.21 − 0.05) = 800A. A = 240/800 = 0.300 m². Ignoring the partial-pressure difference gives 0.048; using the hourly rate with a daily OTR gives 0.0125; using 0.21 as the driving force (0.229) assumes zero O2 inside.
Further reading: Kader (ed.), Postharvest Technology of Horticultural Crops
A condition common to CA, MA and hermetic storage is that
A. It must be gas-tight
Without a seal, air leaks in and the modified atmosphere reverts to air. None requires raised O2, high temperature or prior fumigation.
A horizontal screw conveyor has a 200 mm flight, a 50 mm shaft, 200 mm pitch and runs at 120 rpm with a loading efficiency of 0.4. It conveys wheat of bulk density 750 kg/m³. Capacity?
A. 12.72 t/h
Swept volume per revolution = (π/4)(D² − d²)p = (π/4)(0.2² − 0.05²)(0.2) = 0.005890 m³. × 120 rpm × 0.4 = 0.28274 m³/min. Mass = 0.28274 × 750 × 60 = 12,723 kg/h = 12.72 t/h. Ignoring the shaft gives 13.57; ignoring loading efficiency gives 31.81; treating rpm as rev/s gives 763.4.
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
How does inclining a screw conveyor affect its capacity at constant speed?
D. Capacity falls
As the angle increases, material falls back over the flight and the loading efficiency drops, so capacity falls.
Further reading: Sahay and Singh, Unit Operations of Agricultural Processing
En-masse (chain) conveyors move grain
C. As a continuous mass in an enclosed casing, gently and at moderate capacity
In an en-masse conveyor, flights on a chain drag the material, which moves as a solid mass in the casing, with little damage. The other options describe pneumatic, thrower and vibratory systems.
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