Cochran (vertical multi-tubular) boiler: typical count of fire tubes Select the commonly cited number of small-diameter fire tubes used in the standard textbook Cochran boiler description.

Introduction / Context:
The Cochran boiler is a classic vertical, multi-tubular, fire-tube design widely discussed in boiler courses. Remembering its typical dimensions and tube counts is helpful for quick identification and for estimating heating surface area and gas-side pressure drop in conceptual problems.

Given Data / Assumptions:

• Standard textbook representation of a Cochran boiler (hemispherical crown, multi-tubular fire-tube bank).
• Small-diameter smoke tubes carrying hot gases through a water-filled shell.
• We refer to the typical “exam schematic” configuration rather than proprietary variants.

Concept / Approach:
While practical designs may vary with manufacturer and rating, widely used teaching diagrams list a fire-tube bank numbering around the mid-hundreds. The commonly quoted figure in many exam problems and solved examples is approximately 165 tubes for a representative size, balancing heat transfer area and draft resistance.

Step-by-Step Solution:
Identify that this is a recall item from standard boiler descriptions.Recognize Cochran = vertical shell + multiple small smoke tubes.Recall the typical tube count cited: about 165 tubes.Select 165 as the most standard textbook value among the options provided.

Verification / Alternative check:
Many classroom notes and question banks align around 165 for the common schematic. Real units can have different counts depending on duty and shell size, but exam convention typically expects 165 here.

Why Other Options Are Wrong:
Values 75, 95, and 115 are below typical counts for the standard teaching example; 225 is on the higher side of certain larger variants and is not the commonly cited number for the canonical diagram.

Common Pitfalls:
Assuming a single “true” number across all Cochran boilers; neglecting that exam problems often use a representative standard count for consistency.

Final Answer:
165