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 papersRefrigeration cycles, equipment and cold-store design, from COP to the heat load of a room full of potatoes.
In the exams: GATE AG Section 7 (refrigeration COP/TR in 4 of 8 papers 2019–26; composite cold-store walls recur); ICAR AIEEA-PG Unit VI; ICAR AICE subject 38 Unit 6
ASRB NET — Agricultural Structures & Process Engineering
Conceptual MCQs across the whole subject with an emphasis on cold-storage design, insulation materials, controlled atmosphere and pre-cooling, and standard numerical relations.
How our questions for ASRB NET spread across the units of Refrigeration, Air-Conditioning & Cold-Chain Engineering. Difficulty: 20 easy, 33 medium, 10 hard.
| Refrigerated transport and cold-chain logistics | 8 | |
| Refrigerants: ODP and GWP | 7 | |
| Vapour-absorption refrigeration | 5 | |
| Compressors | 5 | |
| Expansion devices | 5 | |
| Insulation and vapour barriers | 5 | |
| Ice-bank systems | 5 | |
| Condensers and evaporators | 4 | |
| Psychrometric air-conditioning processes | 4 | |
| Cold-store heat load: transmission, product and respiration | 4 | |
| Cold-store heat load: infiltration, occupancy and equipment | 4 | |
| Vapour-compression refrigeration cycle | 3 | |
| Pressure-enthalpy charts | 3 | |
| COP and tonnes of refrigeration | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Subcooling the liquid refrigerant leaving the condenser, with evaporating and condensing pressures unchanged, will
B. Increase the refrigerating effect per kg without increasing compressor work per kg
Subcooling lowers h3, and since h4 = h3 the refrigerating effect h1 − h4 grows. Suction state 1 is unchanged, so the work h2 − h1 is unchanged and COP rises. Throttling being isenthalpic is exactly why the lower h3 carries through to h4.
Further reading: Arora, Refrigeration and Air Conditioning
In the three-fluid (diffusion) absorption refrigerator, hydrogen is used to
B. Equalise total pressure throughout the circuit so that no solution pump is needed
Hydrogen fills the evaporator and absorber so that ammonia evaporates at a low partial pressure while total pressure is uniform; circulation is by a heat-driven bubble pump and gravity. Water, not hydrogen, is the absorbent, and ammonia is the refrigerant.
Further reading: Arora, Refrigeration and Air Conditioning
By the standard numbering rule for halocarbons, chlorodifluoromethane (CHClF2) is designated
D. R-22
R-XYZ: X = C − 1 = 0 (dropped), Y = H + 1 = 2, Z = F = 2, giving R-22. R-12 is CCl2F2 (no hydrogen). R-21 would have only one fluorine. R-122 forgets to subtract 1 from the carbon count (X = C = 1).
Further reading: ASHRAE Standard 34 / ISO 817
Ozone depletion potential (ODP) is expressed relative to
A. R-11, taken as 1.0
ODP compares ozone destruction with that of trichlorofluoromethane, R-11. Carbon dioxide is the reference for global warming potential, not ODP; R-134a and ammonia have ODP zero.
Further reading: ASHRAE Standard 34 / ISO 817
As the evaporating temperature of a reciprocating compressor falls with condensing temperature fixed, its volumetric efficiency
B. Falls, as a higher pressure ratio makes clearance gas re-expand over more stroke
η_v = 1 + C − C(p_d/p_s)^(1/n) falls as p_d/p_s rises. Suction gas actually becomes less dense at lower evaporating temperature, which also reduces mass flow.
Further reading: Arora, Refrigeration and Air Conditioning
When the load on an evaporator fed by an automatic (constant-pressure) expansion valve increases, the valve tends to
A. Close, starving the evaporator just when more refrigerant is needed
Higher load tends to raise evaporator pressure; the valve acts to hold pressure constant, so it throttles down. That inverse response is why it is used only for small, steady loads.
Further reading: Arora, Refrigeration and Air Conditioning
A practical advantage of the capillary tube is that it allows a low-starting-torque compressor motor because
A. High- and low-side pressures equalise through it while the compressor is off
With no valve to close, pressures balance during the off cycle, so the compressor starts against no pressure difference. It has no reserve, no adjustment, and flash gas still forms.
Further reading: Arora, Refrigeration and Air Conditioning
During sensible heating of moist air, which property remains constant?
D. Humidity ratio
No moisture is added or removed, so ω stays constant and the process is horizontal on the chart. Relative humidity falls because the saturation pressure rises; wet-bulb and enthalpy rise.
Further reading: ASABE D271
A room has a sensible heat gain of 30 kW and a latent heat gain of 10 kW. The room sensible heat factor is
A. 0.75
SHF = sensible/(sensible + latent) = 30/40 = 0.75. 3 is the sensible-to-latent ratio, not the SHF. 0.33 is latent/sensible (10/30), and 0.25 is latent/total (10/40).
Further reading: Arora, Refrigeration and Air Conditioning
In the cold chain, the step that removes field heat from produce immediately after harvest is called
A. Pre-cooling
Pre-cooling (forced-air, hydro, vacuum, room or ice cooling) brings produce quickly toward storage temperature. Curing heals wounds at warm temperatures; blanching is a heat treatment before freezing vegetables.
Further reading: ASHRAE Handbook — Refrigeration
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