Question Statement:
One side of a solid food block of 10 cm thickness is subjected to a heating medium having a film heat transfer coefficient of 70 W·(m²·°C)⁻¹. The other side of the food block is being cooled by a medium having a film heat transfer coefficient of 100 W·(m²·°C)⁻¹. The food block is having a thermal conductivity of 0.2 W·(m·°C)⁻¹ and the contact area of the block available for heat transfer is 1 m². Heat transfer rate in the block at steady state is 100 J·s⁻¹. The temperature difference between the two sides of the block in °C is ______. [round off to 2 decimal places]
Step-by-Step Solution & Explanation
"Temperature difference between the two sides" refers to the overall driving force between the two bulk heating/cooling media, spanning both convective films and the solid block (all three resistances in series). Total thermal resistance (per unit area) R_total = 1/h₁ + L/k + 1/h₂ = 1/70 + 0.10/0.2 + 1/100 = 0.01429 + 0.5 + 0.01 = 0.5243 °C·m²/W. ΔT_total = q×R_total/A = 100×0.5243/1 = 52.43 °C.
Appendix A — Consolidated Answer Table
All 65 questions (10 General Aptitude + 55 Agricultural Engineering), listed in original paper Q. No. order.
Appendix B — Section-wise Weightage & Preparation Observations
Preparation Observations
Section 4 (Soil and Water Conservation Engineering) carries the single highest weightage (21%, 13 questions) — it spans Fluid Mechanics, Soil Mechanics, Hydrology, Surveying and Soil/Water Erosion, so it rewards broad, even coverage rather than depth in one sub-area alone.
Section 6 (Agricultural Process Engineering) is the second-highest weightage area (16%, 10 questions), concentrated in Size Reduction/Material Handling and Storage Systems — Bond's Law, mass-transfer/membrane problems, and Janssen's bin-pressure equation recur as core numerical themes.
General Aptitude (15%) and Engineering Mathematics (10%) together make up a quarter of the paper and are largely formula-recall or short-computation questions — high-value, low-time-cost marks if fundamentals (limits, matrices, probability, ODEs) are solid.
Farm Machinery and Farm Power together contribute 22% and are numerically heavy (drafts, gear/pump torque, engine ratios, traction) — practicing unit conversions (kN↔N, cm↔m, rpm↔rev/s) is essential since most errors in this paper stem from unit-handling rather than concept gaps.
Irrigation & Drainage and Dairy & Food Engineering are comparatively lower-weightage (8% each) but still each carry 5-6 questions — Darcy's Law/Thiem equation problems and General-Method sterilization-lethality calculations are recurring numerical patterns worth mastering, as they reappear across multiple GATE AG years.
Several NAT answers in this paper (Q.20, Q.24, Q.32, Q.48, Q.54) showed a small but non-trivial gap between the independently re-derived value using standard textbook formulae and the officially published range — a useful reminder to double-check assumption choices (e.g., which of several near-equivalent formula variants an examiner used) when self-practicing against old keys.