Boiler classification by gas and water paths: In a fire-tube boiler, which flow arrangement correctly describes the relative paths of hot gases and water?

Introduction / Context:
Boilers are broadly divided into fire-tube and water-tube types. The distinction rests on whether hot gases or water/steam occupy the tubes. This affects heat transfer area, response time, and allowable pressure.

Given Data / Assumptions:

• Fire-tube: gas-in-tube, water-outside configuration.
• Water-tube: water-in-tube, gas-outside configuration.
• Typical fire-tube examples: Lancashire, Cornish, Locomotive, Scotch marine.

Concept / Approach:
In fire-tube boilers, combustion products pass through multiple small tubes immersed in the boiler shell water. Heat transfers from the hot gas inside the tubes to the surrounding water, generating steam. This configuration yields large water content and stable but slower response compared to water-tube designs.

Step-by-Step Solution:
Identify class: “fire-tube” means fire/gas in the tubes.Describe path: flames and hot gases inside tubes; water surrounds tubes in shell.Eliminate alternatives: water-in-tube describes water-tube boilers; forced circulation is not inherent to fire-tube design.Select the matching statement.

Verification / Alternative check:
Standard diagrams of locomotive and Scotch marine boilers show banks of gas-carrying tubes through a water-filled shell.

Why Other Options Are Wrong:
Option (b) is the water-tube arrangement; (c) confuses circulation methods; (d) and (e) do not match standard classifications.

Common Pitfalls:
Mixing up the two major classes or assuming forced circulation applies to fire-tube boilers.

Final Answer:
the flames and hot gases pass through the tubes which are surrounded by water