Boiler Classification by Water/Fire Path Which one of the following is a water-tube boiler (water inside tubes, hot gases outside)?

Introduction / Context:
Boilers are broadly classified as water-tube and fire-tube types. In water-tube boilers, water flows through tubes heated externally by hot gases; in fire-tube boilers, hot gases pass through tubes surrounded by water. Correct identification is essential for understanding pressure capability, response, and typical applications.

Given Data / Assumptions:

• Standard textbook boiler designs.
• No special hybrid arrangements assumed.

Concept / Approach:
The Babcock and Wilcox is a classic water-tube boiler featuring inclined water tubes connected to headers and a drum, with hot gases flowing around the tubes. Lancashire, Locomotive, and Cochran boilers are fire-tube types where flue gases pass through large tubes within a water shell.

Step-by-Step Solution:
Identify flow path for each option.Babcock and Wilcox → water in tubes; gases outside → water-tube.Others listed → fire-tube designs.

Verification / Alternative check:
Operating pressure capability and quick steaming behavior match water-tube characteristics of Babcock and Wilcox units.

Why Other Options Are Wrong:
Lancashire / Locomotive / Cochran: all are fire-tube; water surrounds the tubes while gases pass through them.

Common Pitfalls:
Equating shell shape (horizontal/vertical) with tube arrangement; the classification is based on where water flows.

Final Answer:
Babcock and Wilcox boiler