Question Statement:
In a continuous belt freezer, fish fillet at a feed rate of 1000 kg h⁻¹ is frozen. The unfrozen fish having moisture content of 85% (wet basis) enters the freezer at 25°C and complete frozen fish exits at –20°C. Properties of fish are: latent heat of crystallization = 330 kJ kg⁻¹, fixed freezing point = − 2.5°C, density = 1100 kg m⁻³, specific heat capacity above freezing point=3.60 kJ kg⁻¹ K⁻¹ and specific heat capacity below freezing point = 1.97 kJ kg⁻¹ K⁻¹. Neglecting other heat losses in the freezer, the power requirement of the compressor (in kW) having a coefficient of performance of 2.50 is,
Options:
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(A) 43.8
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(B) 46.0
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(C) 51.5
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(D) 61.7
Step-by-Step Solution & Explanation
Heat to be removed per kg of fish, in three stages:
1) Sensible cooling, 25°C → −2.5°C (above-freezing region): q₁ = 3.60×(25−(−2.5)) = 3.60×27.5 = 99.0 kJ/kg
2) Latent heat of freezing: q₂ = 330 kJ/kg
3) Sensible cooling, −2.5°C → −20°C (below-freezing region): q₃ = 1.97×((−2.5)−(−20)) = 1.97×17.5 = 34.475 kJ/kg
Total, q = 99.0+330+34.475 = 463.475 kJ/kg.
Refrigeration load = 1000 kg/h × 463.475 kJ/kg = 463,475 kJ/h = 128.74 kW.
Compressor power = Refrigeration load / COP = 128.74/2.50 = 51.5 kW. Answer: (C).
Appendix A — Consolidated Answer & Topic Table
Appendix B — Section-wise Weightage & Preparation Observations
Preparation Observations
GA carries a fixed 15% weight (10 questions / 15 marks) every year; treat it as a high-ROI, low-syllabus-depth block — quick daily practice on verbal reasoning, data interpretation and simple quantitative aptitude yields disproportionate score gains relative to preparation time.
Section 4 (Soil & Water Conservation Engineering) and Section 5 (Irrigation & Drainage Engineering) together dominate the subject paper in this set, spanning fluid mechanics, surveying, hydrology, erosion control and irrigation/drainage/groundwater design — these should receive the largest sustained study block, with particular attention to numerical (NAT) design-formula problems (Thiem equation, Manning's equation, rational-method runoff, drip/sprinkler system sizing), which recur almost every year.
Section 3 (Farm Power) and Section 2 (Farm Machinery) questions in this set were dominated by applied numericals (Morse test, volumetric efficiency, field efficiency, gear ratios, clutch torque) rather than pure theory — mastering the standard formula set and unit-conversion discipline (rpm↔rad/s, L/min↔m³/s, kPa↔Pa) is more valuable than memorising definitions alone.
Section 6 and Section 7 (Process/Dairy/Food Engineering) questions leaned heavily on mass-and-energy balance style numericals (moisture-content balances, refrigeration load, lumped-capacitance heating, separator effectiveness) — practice setting up basis-1-hour/1-kg mass balances quickly, as most marks are lost to balance-equation setup errors rather than arithmetic.
Section 1 (Engineering Mathematics) questions were computationally short but appeared across every sub-topic (linear algebra, vector calculus, PDE classification, probability, definite integrals) — since these are typically quick, high-certainty marks, they should be attempted first in the exam to bank early confidence and time.
NAT (numerical answer type) questions carry no negative marking, unlike MCQs (−⅓ mark for a 1-mark MCQ, −⅔ for a 2-mark MCQ) — for borderline/uncertain questions, prioritise attempting NAT items even under time pressure, and apply elimination-based guessing only for MCQs where at least two options can be confidently ruled out.
A small number of this set's questions rely on specialised design-handbook formulae not derivable from first principles alone (e.g. bench-terrace earthwork with battered risers, nozzle application-rate scaling, grain-recycle load in a two-product separator) — these are worth flagging in study notes as 'formula-recall' items to memorise directly from a standard reference (e.g. Ram Babu et al. for soil conservation engineering) rather than re-derived under exam time pressure.