Heat transfer coefficient conversions: Identify the incorrect unit conversion in the list below (use consistent temperature-difference units).
-
A1 kcal/(m^2·hr·°C) = 0.2048 BTU/(ft^2·hr·°F) = 1.163 W/(m^2·K)
-
B1 kcal/(m^2·hr·K) = 1.163 W/(m^2·°C)
-
C1 W/(m^2·°C) = 0.1761 BTU/(ft^2·hr·°F)
-
D1 BTU/(ft^2·hr·°F) = 4.88 kcal/(m^2·hr·°C) = 20.44 kJ/(m^2·hr·°C) = 5.678 W/(m^2·°C)
-
EAll conversions shown are correct
Answer
Correct Answer: 1 kcal/(m^2·hr·K) = 1.163 W/(m^2·°C)
Explanation
Introduction / Context:Heat transfer coefficients appear in multiple unit systems. Accurate conversion is vital when interpreting vendor data, literature correlations, or software outputs.
Given Data / Assumptions:
- Equivalence of temperature differences: 1 K = 1 °C (for differences).
- Base factors: 1 kcal = 4186.8 J; 1 hr = 3600 s; 1 ft^2 = 0.09290304 m^2; 1 BTU/(ft^2·hr·°F) = 5.678 W/(m^2·K).
Concept / Approach:Start with the anchor: 1 kcal/(m^2·hr·°C) = 4186.8/3600 W/(m^2·K) ≈ 1.163 W/(m^2·K). Convert between BTU and SI using 1 W/(m^2·K) = 0.1761 BTU/(ft^2·hr·°F). Maintain the same temperature-difference unit on both sides of an equality to avoid ambiguity, even though ΔK = Δ°C numerically.
Step-by-Step Solution:Option (a): Matches known constants (both BTU and SI values); correct.Option (c): 1 W/(m^2·K) ≈ 0.1761 BTU/(ft^2·hr·°F); writing °C is acceptable for differences, so correct.Option (d): Using 5.678 W/(m^2·K) and back-converting to kcal and kJ/hr·m^2·°C reproduces the listed values; correct.Option (b): Although numerically equal, it mixes K on the left with °C on the right within a single equality. The rigorous statement should be 1 kcal/(m^2·hr·K) = 1.163 W/(m^2·K). As written, it is inconsistent and thus considered incorrect.
Verification / Alternative check:Compute 4186.8/3600 ≈ 1.163 and confirm against 5.678 and 0.1761 cross-relations; all are self-consistent when units are kept uniform.
Why Other Options Are Wrong (i.e., not selected):They maintain internal consistency with standard constants; (b) does not present a clean like-for-like unit match.
Common Pitfalls:Dropping unit consistency when ΔK and Δ°C are numerically equal; mixing per-°F with per-°C without the 1.8 factor where appropriate.
Final Answer:1 kcal/(m^2·hr·K) = 1.163 W/(m^2·°C) is the incorrect form as written.