Question Statement:
Ice cream at a temperature of −18 °C is being transported through a refrigerated truck having outside dimensions of 6 m length, 3 m width and 2 m height. The truck is traveling at a speed of 90 km h⁻¹ on a highway where the air temperature is 45 °C. The truck is insulated in a way such that the outside surface temperature of the truck is maintained at 15 °C. Assume that there is no heat transfer from the front and back of the truck. Properties of air at 30 °C are: ρ = 1.1514 kg m⁻³, μ = 1.86 × 10⁻⁵ Pa s, C_p = 1.007 kJ kg⁻¹ K⁻¹, k = 0.0265 W m⁻¹ K⁻¹. Use the relation: Nu = 0.036 Re^0.8 Pr^0.33. The rate of heat transfer at the four surfaces is
Options:
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(A) 47.8 kW
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(B) 86.1 kW
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(C) 95.7 kW
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(D) 114.7 kW
Step-by-Step Solution & Explanation
Four heat-transfer surfaces (two sides + top + bottom, front/back excluded per the problem statement): Side area (each) = L×H = 6×2 = 12 m² (×2 sides = 24 m²); top/bottom area (each) = L×W = 6×3 = 18 m² (×2 = 36 m²). Total A = 24+36 = 60 m². ΔT = T_air − T_surface = 45−15 = 30 K. Q = h·A·ΔT = 53.18×60×30 = 95,724 W = ≈95.7 kW.
Appendix A — Consolidated Answer Table
(*No official answer key was supplied with this task — the "Computed Ans." column is this document’s independently derived and cross-checked answer, not an official key. Topic column is truncated for table width; see the full syllabus-quoted topic line in each question’s entry in the main body above.)
Appendix B — Section-wise Weightage & Preparation Observations
Preparation Observations
Soil and Water Conservation Engineering (Section 4) carries the single largest share of marks (22.0%) in this paper, spanning fluid mechanics, soil mechanics, hydrology and surveying — candidates should prioritise fluency across all four of these sub-areas rather than any one alone.
Dairy and Food Engineering (Section 7) is the second-largest block (20.7%), dominated by heat/mass transfer numericals (conduction, convection, fin/insulation problems) and microbial death-kinetics (D/z-value) calculations — both are highly formula-driven and reward careful unit tracking.
Farm Power (Section 3) and Farm Machinery (Section 2) together account for over 31% of the paper, with a strong emphasis on numerical problems (engine cycles, tractor traction mechanics, machine-element design) rather than descriptive recall.
Engineering Mathematics (Section 1) is comparatively lightly weighted here (5.3%) but the questions drawn (Laplace transforms, Euler’s method, Simpson’s rule, probability) are representative of the kind of direct, single-concept numericals typically seen — quick, error-free computation is the key skill, not derivation.
A recurring pattern across sections is unit-consistency errors as the most common distractor mechanism (e.g., mixing kPa/Pa, l/s vs m³/s, mm vs m) — options are frequently constructed to match a plausible but unit-inconsistent calculation, so deliberate unit-checking before selecting an answer is high-value exam technique.
Several questions (Q54, Q73, Q82) required judgement calls where more than one standard convention could apply (turbulent vs laminar flow assumption, cone-index vs fixed-coefficient rolling resistance, and rounding in the z–activation-energy relation respectively); these are flagged explicitly in this document rather than silently resolved, since no official key was available to adjudicate.