Cochran Boiler — Fire-Tube Diameter In a vertical Cochran fire-tube boiler, the usual outside diameter of the individual fire tubes is approximately:

Introduction / Context:
The Cochran boiler is a compact, vertical fire-tube boiler. Recognizing typical tube sizes is useful for heat-transfer surface estimation, gas-side pressure drop, and maintenance considerations like soot blowing and tube cleaning.

Given Data / Assumptions:

• Standard Cochran boiler proportions.
• Fire (smoke) tubes carry hot gases; water surrounds the tubes.

Concept / Approach:
Typical Cochran designs employ tube diameters of the order of a few centimeters to balance heating surface with gas velocity and allowable pressure drop. A widely quoted nominal size is about 62.5 mm (approximately 2.5 inches), offering a practical compromise between cleaning access and heat transfer rate.

Step-by-Step Solution:
Recall standard tube size from design handbooks: ~62.5 mm.Compare with alternatives: 6.25 mm is far too small; 72.5 or 92.5 mm are larger than typical for compact vertical units.Select 62.5 mm as the representative size.

Verification / Alternative check:
Historic specifications of Cochran boilers list tube outside diameters around 2–3 inches, aligning with 62.5 mm.

Why Other Options Are Wrong:
6.25 mm: impractically small for gas passages and cleaning.72.5 mm or 92.5 mm: unusually large for the standard compact Cochran configuration.

Common Pitfalls:
Confusing fire-tube size with water-drum or furnace dimensions.

Final Answer:
62.5 mm