ASRB NET — Farm Machinery & Power / Land & Water Management Engineering / Agricultural Structures & Process Engineering · India · Agricultural Scientists Recruitment Board (ICAR)
Original practice questions written to the published syllabus · not past papersThe physical, frictional, aerodynamic, thermal, rheological and electrical properties of grains, fruits and foods that every machine and process is designed around.
In the exams: GATE AG Section 6 (first syllabus line; rheology in 4 of 8 papers 2019–26); ICAR AICE subject 41 Unit 1; NCEES PE properties of biological materials
ASRB NET — Agricultural Structures & Process Engineering
Conceptual MCQs on property definitions and measurement methods (platform scale, toluene displacement, air-comparison pycnometer, tilting table, vertical wind tunnel, DSC), and on how properties are used in design of cleaners, bins, dryers and conveyors.
How our questions for ASRB NET spread across the units of Engineering Properties of Agricultural Produce. Difficulty: 33 easy, 39 medium, 8 hard.
| Viscoelastic models | 10 | |
| Electrical and optical properties | 10 | |
| Volume and density: bulk and true | 9 | |
| Water activity | 9 | |
| Size and shape: sphericity and roundness | 8 | |
| Thermal properties: specific heat, conductivity and diffusivity | 8 | |
| Frictional properties: angle of repose and coefficient of friction | 7 | |
| Aerodynamic properties: terminal velocity | 7 | |
| Porosity | 6 | |
| Rheology: Newtonian and non-Newtonian flow | 6 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Curray's roundness of a fruit resting in its natural position is calculated as
D. projected area of the fruit divided by the area of the smallest circle circumscribing the projection
Curray's roundness = A_p / A_c. The geometric mean over major diameter is Mohsenin's sphericity, not roundness. Wadell's roundness divides the summed corner radii by N R, rather than multiplying. Surface-to-volume ratio is a different shape index used in heat and mass transfer.
Further reading: Mohsenin, Physical Properties of Plant and Animal Materials
Why do bin design standards apply an overpressure factor to the static Janssen lateral pressure?
C. Because flow of grain during emptying produces wall pressures above the static values
Flow during discharge changes the stress state and produces lateral pressures higher than the static fill values, so codes multiply by an overpressure factor whose value differs between standards. The factor increases, not reduces, design pressure; bulk density rises with compaction rather than falling; and the vertical-to-lateral conversion uses k, not an overpressure factor.
Further reading: ASABE S433.1
A kernel is treated as a sphere of diameter 5 mm and density 1300 kg/m³ falling in air of density 1.2 kg/m³ with a constant drag coefficient of 0.44 (Newton regime). Its terminal velocity, V_t = [4 g d (ρ_p − ρ_f)/(3 C_d ρ_f)]^(1/2), is
D. 12.7 m/s
V_t² = 4 × 9.81 × 0.005 × 1298.8 / (3 × 0.44 × 1.2) = 160.9; V_t = 12.7 m/s. 9.0 m/s comes from using 2 instead of 4 in the numerator; 983 m/s applies Stokes' law (air viscosity 1.8 × 10⁻⁵ Pa·s) far outside its Reynolds-number range; 0.39 m/s puts particle density in the denominator instead of air density.
Further reading: Mohsenin, Physical Properties of Plant and Animal Materials
Pneumatic conveying of grain in dilute phase requires that the conveying air velocity be
D. greater than the terminal velocity of the grain, with a design margin to prevent settling
Kernels stay in suspension only if the air moves faster than their terminal velocity; designers add a margin because bends and particle interactions cause settling. Half the terminal velocity would drop the grain; air slower than the chaff's terminal velocity lifts nothing; pressure without adequate velocity does not keep particles suspended.
Further reading: Mohsenin, Physical Properties of Plant and Animal Materials
A dough has a relaxation time of 100 s. During 1-second mixing strokes it behaves elastically, but over a 1-hour proof it flows. This is explained by
B. the Deborah number λ/t_obs, far above 1 during mixing and far below 1 during proofing
De = 100/1 = 100 during mixing (solid-like) and 100/3600 ≈ 0.03 over the proof (liquid-like). The Reynolds number concerns inertia against viscosity in flow, the Biot number concerns heat-transfer resistances, and a change in n is not what makes dough flow on resting.
Further reading: Steffe, Rheological Methods in Food Process Engineering
On the force-deformation curve of an apple compressed between plates, the bioyield point is where
D. deformation increases with no increase or a decrease in force, marking the start of cell rupture
Bioyield is the point of internal failure of cells, reached before the macroscopic rupture point, and it is the practical handling limit. Visible splitting is the rupture point; first contact is the start of the test; the steepest initial slope is used for modulus, not bioyield.
Further reading: Mohsenin, Physical Properties of Plant and Animal Materials
A food has a dielectric constant ε' = 52 and a dielectric loss factor ε'' = 15 at 2450 MHz. Its loss tangent is
D. 0.288
tan δ = ε''/ε' = 15/52 = 0.288. 3.467 inverts the ratio; 0.224 divides by the sum; 0.780 multiplies the two, which has no meaning.
Further reading: Rao, Rizvi, Datta and Ahmed (eds.), Engineering Properties of Foods
Two batches of dried mango differ by ΔL* = −3, Δa* = 4 and Δb* = −12. The total colour difference ΔE = √(ΔL*² + Δa*² + Δb*²) is
C. 13.0
ΔE = √(9 + 16 + 144) = √169 = 13.0. 19.0 adds the absolute differences; −11.0 adds the signed differences; 169.0 forgets the square root.
Further reading: Sahin and Sumnu, Physical Properties of Foods
A shelf-stable snack bar has a water activity of 0.83. Using the general minimum water activities for growth given in food microbiology texts, which group is the main spoilage risk?
A. Moulds, many growing down to about 0.80
Most spoilage bacteria need about 0.90–0.91, yeasts about 0.88, and most moulds about 0.80, so at 0.83 moulds are the chief threat. Bacteria do not grow at 0.70; xerophilic moulds and osmophilic yeasts can grow down to about 0.6, so 'no microbes below 0.90' is wrong; moulds tolerate lower a_w than yeasts, not higher. Limits shift with pH, temperature and preservatives.
Further reading: Fennema's Food Chemistry; Beuchat, minimum water activity for microbial growth
Which saturated salt solution at 25 °C holds the relative humidity closest to 75% in a desiccator used for isotherm work?
D. Sodium chloride
Saturated NaCl gives about 75% RH at 25 °C. Lithium chloride gives about 11%, magnesium chloride about 33% and potassium sulfate about 97%; the values change slightly with temperature.
Further reading: Greenspan, Humidity fixed points of binary saturated aqueous solutions
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