Unit conversions in heat transfer rate: identify the incorrect equivalence among Watt, kcal/hr, BTU/ft^2·hr, and kcal/m^2·hr.

Difficulty: Easy

Correct Answer: 1 Watt = 1.163 kcal/hr

Explanation:


Introduction / Context:
Thermal calculations often require converting among SI and FPS engineering units. A frequent source of error is inverting ratios or mixing area conversions. This question checks consistency across common heat-flow units.



Given Data / Assumptions:

  • 1 kcal = 4184 J.
  • 1 hour = 3600 s.
  • 1 BTU = 1055.06 J; 1 ft^2 = 0.092903 m^2.



Concept / Approach:
Convert one base pair precisely and propagate. Since 1 kcal/hr = 4184/3600 W ≈ 1.163 W, the inverse is 1 W ≈ 0.860 kcal/hr, not 1.163 kcal/hr. For surface rates, convert energy and area consistently, confirming the tabulated factors.



Step-by-Step Solution:
Compute: 1 kcal/hr = 4184/3600 ≈ 1.163 W → correct.Invert: 1 W = 3600/4184 ≈ 0.860 kcal/hr → option (b) is wrong.Check: 1 BTU/ft^2·hr to kcal/m^2·hr: multiply by 10.7639 m^2/ft^2 and 0.252164 kcal/BTU → ≈ 2.712 → correct.Check: 1 kcal/m^2·hr to BTU/ft^2·hr: 3.9683/10.7639 ≈ 0.3687; and to W/m^2: 1.163 → correct.



Verification / Alternative check:
Cross-validate with standard tables; the only inconsistent statement remains option (b).



Why Other Options Are Wrong:
(a), (c), (d) match precise conversions; thus they are not “wrong.”



Common Pitfalls:
Forgetting to invert factors; mixing per-area conversions; rounding beyond significant figures.



Final Answer:
1 Watt = 1.163 kcal/hr


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