ICAR AIEEA-PG / PGS — Code 18 Food Science Technology · India · ICAR through the National Testing Agency
Original practice questions written to the published syllabus · not past papersThe mechanical operations that clean, sort, reduce, mix, homogenise and separate food materials, including filtration, centrifugation and membrane processes, with the design equations used to size them.
In the exams: GATE XE-G Section 4 (mechanical operations); ICAR AIEEA-PG Code 18 Unit II (cleaning, sorting, size reduction, mixing, separation, filtration, membranes)
ICAR AIEEA-PG / PGS — Code 18 Food Science Technology
Unit II lists cleaning, de-husking, sorting and grading, peeling, size reduction, mixing and forming, separation, filtration and membrane processes, expression, extraction and leaching, crystallisation and distillation. MCQs test principles, equipment types and applications (hammer vs roller mills, disc-stack vs decanter, MF/UF/NF/RO, filter aids, flash-steam vs lye peeling) and short calculations.
How our questions for ICAR AIEEA-PG / PGS spread across the units of Mechanical Unit Operations: Size Reduction, Mixing & Separation. Difficulty: 17 easy, 51 medium, 2 hard.
| Membrane processes: microfiltration, ultrafiltration, nanofiltration and reverse osmosis | 7 | |
| Mixing of solids, pastes and liquids; agitation and power number | 6 | |
| Cleaning, sorting and grading of raw materials | 5 | |
| Size reduction: energy laws of Rittinger, Kick and Bond | 5 | |
| Size-reduction equipment for dry and wet foods | 5 | |
| Centrifugation and centrifugal separators | 5 | |
| Expression and solid-liquid extraction | 5 | |
| Crystallisation | 5 | |
| Peeling methods | 4 | |
| High-pressure homogenisation | 4 | |
| Settling and sedimentation | 4 | |
| Filtration: cake filtration theory and filter aids | 4 | |
| Distillation and supercritical fluid extraction | 4 | |
| Material handling: conveyors and elevators for foods | 4 | |
| Sieving and particle-size analysis | 3 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Aspiration (winnowing) separates chaff and dust from grain mainly by differences in
A. terminal velocity in an air stream
Light chaff has a lower terminal velocity and is carried away by air while grain falls. Colour sorters and magnets use other properties.
Further reading: Fellows, Food Processing Technology
Sorting differs from grading in that sorting
D. separates by one measurable property
Sorting uses a single property such as size, weight or colour; grading assesses several quality attributes together against standards.
Further reading: Fellows, Food Processing Technology
Wheat flour milling relies mainly on
B. roller mills combining compression and shear
Pairs of fluted break rolls and smooth reduction rolls, running at different speeds, separate endosperm from bran gradually.
Further reading: Fellows, Food Processing Technology
In the turbulent regime in a baffled tank, doubling impeller speed increases power by a factor of
D. 8
P ∝ N³ when Np is constant; 32 is the factor for doubling diameter (D⁵).
Further reading: McCabe, Smith and Harriott, Unit Operations of Chemical Engineering
Segregation in dry-mix blending is most likely when ingredients differ greatly in
B. particle size and density
Small or dense particles percolate downward during handling; matching sizes and adding a little liquid reduce segregation.
Further reading: Fellows, Food Processing Technology
By Stokes' law, the settling velocity of a small particle is proportional to
B. the square of its diameter
v = d²Δρg/18μ, so velocity varies with the square of diameter; doubling d gives four times the settling velocity.
Further reading: Geankoplis, Transport Processes and Separation Process Principles
In constant-pressure filtration with negligible medium resistance, collecting 1 m³ of filtrate takes 10 min. Collecting 2 m³ takes
A. 40 min
t ∝ V², so t = 10 × 2² = 40 min. 20 min assumes t ∝ V; 14 min uses √2; 80 min uses V³.
Further reading: Geankoplis, Transport Processes and Separation Process Principles
Concentration polarisation in membrane filtration is reduced mainly by
C. high cross-flow velocity over the membrane
Cross-flow sweeps the boundary layer of retained solutes from the surface; dead-end operation builds a cake.
Further reading: Cheryan, Ultrafiltration and Microfiltration Handbook
The critical point of carbon dioxide used in supercritical extraction is about
A. 31 °C and 7.4 MPa
CO₂ critical point is about 31.1 °C and 7.38 MPa; 374 °C and 22 MPa is water's; −78.5 °C is the CO₂ sublimation point at atmospheric pressure.
Further reading: McCabe, Smith and Harriott, Unit Operations of Chemical Engineering
Continuous-discharge bucket elevators are preferred to centrifugal-discharge types for
B. fragile or dusty materials
They run slower, and material slides off onto the preceding bucket, reducing damage and dust.
Further reading: Fellows, Food Processing Technology
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