ICAR AIEEA-PG — Agricultural Engineering & Technology (Major Subject Group 10) · India · National Testing Agency for ICAR
Original practice questions written to the published syllabus · not past papersEnergy, work, heat and the cycles behind engines, refrigerators and dryers.
In the exams: GATE AG Section 3 (thermodynamic principles of IC engines); ICAR AIEEA-PG Unit III; NCEES FE thermodynamics and heat transfer 9–14 questions
ICAR AIEEA-PG — Agricultural Engineering & Technology
Unit III sets single-answer MCQs across the whole subject: definitions (intensive/extensive, quasi-static, path functions), statements of the zeroth, first and second laws, Carnot efficiency and COP, polytropic-process relations, steam-table terms (dryness fraction, critical point, Mollier chart), air-standard efficiency formulas and comparisons, VCR components and the tonne of refrigeration, and psychrometric definitions. Negative marking rewards exact definitions and quick one-step calculations.
How our questions for ICAR AIEEA-PG spread across the units of Engineering Thermodynamics. Difficulty: 34 easy, 41 medium, 21 hard.
| Second law, entropy and the Carnot cycle | 13 | |
| First law of thermodynamics | 11 | |
| Properties of steam, steam tables and the Mollier chart | 11 | |
| Air-standard cycles: Otto, Diesel, dual and Brayton | 11 | |
| Vapour-compression cycle basics | 11 | |
| Introduction to psychrometry | 11 | |
| Systems, properties and the zeroth law | 10 | |
| Ideal gas processes | 10 | |
| Steady-flow energy equation | 8 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Which description fits a closed system (control mass)?
A. Energy may cross its boundary as heat or work, but no mass crosses it
A closed system has a fixed mass; heat and work can still cross its boundary. Allowing neither mass nor energy describes an isolated system, and mass flowing across the boundary (as in a pump) makes it an open system or control volume.
Further reading: P.K. Nag — Engineering Thermodynamics
The zeroth law of thermodynamics provides the basis for
B. measuring temperature with a thermometer
The zeroth law says two bodies each in thermal equilibrium with a third are in equilibrium with each other; the thermometer is that third body, so the law makes temperature measurement meaningful. Energy conservation is the first law, the direction of heat flow is the second law, and the entropy reference is the third law.
Further reading: P.K. Nag — Engineering Thermodynamics
Enthalpy is defined as
D. H = U + PV
Enthalpy is H = U + PV, the combination that appears in constant-pressure and flow processes. U − PV has no standard meaning, Q − W is the change in U from the first law, and U + TS is not a standard function (the Helmholtz function is U − TS).
Further reading: Çengel, Boles and Kanoğlu — Thermodynamics: An Engineering Approach
Steam enters an adiabatic nozzle at negligible velocity and its enthalpy falls by 200 kJ/kg. The exit velocity is about
C. 632 m/s
V2 = √(2Δh) with Δh in J/kg: √(2 × 200 000) = 632 m/s. 447 m/s drops the factor 2, 20.0 m/s forgets to convert kJ to J, and 14.1 m/s makes both mistakes.
Further reading: Çengel, Boles and Kanoğlu — Thermodynamics: An Engineering Approach
For a reversible process, the area under the process curve on a T–s diagram represents
D. the heat transferred during the process
For a reversible process δQ = T ds, so ∫T ds is the heat. Work is the area under a P–v curve; enthalpy and internal energy changes are not, in general, areas under a T–s line.
Further reading: Çengel, Boles and Kanoğlu — Thermodynamics: An Engineering Approach
A heat-pump dryer delivers heat at 60 °C while drawing heat from air at 10 °C and has a measured COP of 3.5. Its second-law (exergetic) efficiency relative to a Carnot heat pump between the same temperatures is about
B. 53 %
COP_HP,Carnot = TH/(TH − TL) = 333.15/50 = 6.66; η_II = 3.5/6.66 = 53 %. 62 % uses the refrigerator Carnot COP TL/(TH − TL), 292 % uses Celsius temperatures (60/50), and 15 % is the Carnot engine efficiency between the two temperatures, not a heat-pump comparison.
Further reading: Çengel, Boles and Kanoğlu — Thermodynamics: An Engineering Approach
On a Mollier (h–s) chart, constant-pressure lines inside the wet region are straight because
C. their slope ∂h/∂s at constant pressure equals the saturation temperature, which is constant there
From T ds = dh − v dP, at constant pressure dh/ds = T; in the wet region T = Tsat is constant, so the lines are straight. Enthalpy and entropy both change with quality during boiling, and the Mollier chart uses linear axes.
Further reading: IAPWS-IF97 steam properties; any standard steam table
In the Diesel cycle the cut-off ratio is defined as
D. the volume at the end of heat addition divided by the volume at its start
Cut-off ratio rc = V3/V2, the expansion during constant-pressure heat addition. Total volume over clearance volume is the compression ratio, the pressure ratio describes the constant-volume part of a dual cycle, and the last ratio has no standard name.
Further reading: Çengel, Boles and Kanoğlu — Thermodynamics: An Engineering Approach
If the evaporator temperature of a cold store is lowered while the condensing temperature stays the same, the COP of the plant
B. decreases, because compressor work per kg rises and refrigerating effect falls
A lower evaporator pressure means a larger pressure ratio (more work per kg) and, usually, a smaller refrigerating effect, so COP falls — as the Carnot COP TL/(TH − TL) also shows. Suction vapour density actually falls, reducing capacity.
Further reading: Stoecker and Jones — Refrigeration and Air Conditioning
Air at 30 °C has a vapour pressure of 2.0 kPa. The saturation pressure of water at 30 °C is 4.247 kPa. The relative humidity is about
C. 47.1 %
φ = pv/psat = 2.0/4.247 = 47.1 %. 2.0 % divides by barometric pressure, 212 % inverts the ratio, and 46.0 % is the degree of saturation W/Ws, which is close to but not the same as relative humidity.
Further reading: ASHRAE Handbook — Fundamentals, Psychrometrics
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