GATE 2025 Chemical Engineering, Q17 · Heat Transfer
The correct answer is B, (i) thin-walled, (ii) high.
Question
In industrial heat exchanger design, the overall heat transfer coefficient U is estimated from the equation 1/U 1/hₒ, where and hₒ are the convective heat transfer coefficients on the inner and outer side of the tube, respectively. This is valid for (i) ___ tube of (ii) ___ thermal conductivity. Which one of the following is the CORRECT option to fill in the gaps (i) and (ii)?
Official answer: (i) thin-walled, (ii) high
Why
GATE 2025 official key: (B). Neglecting wall conduction resistance (as this simplified equation does) is only valid for a thin-walled tube made of a high thermal conductivity material, where the wall resistance is negligible.
Explanation cross-checked for consistency. Final answer matches the official IIT answer key.