Babcock and Wilcox (water-tube) boiler — orientation of water tubes: In a standard Babcock and Wilcox boiler, how are the water tubes arranged relative to the horizontal?

Introduction:
Recognizing the geometric arrangement of tubes helps identify boiler type and predict circulation behavior. The Babcock and Wilcox boiler is a classic water-tube design whose tube inclination promotes natural circulation and effective heat transfer.

Given Data / Assumptions:

• Conventional Babcock and Wilcox layout with drums, headers, and tube banks.
• Natural circulation under steady firing.

Concept / Approach:
In this boiler, the straight tubes are set at a small inclination (often about 15° to the horizontal). Hot gases flow externally across the tube bank, while water/steam mixture rises through the inclined tubes toward the steam drum, aiding separation and circulation.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer drawings show the characteristic inclined tube bank feeding the upper steam drum, confirming the orientation.

Why Other Options Are Wrong:

• Vertical/horizontal: do not represent the standard Babcock and Wilcox geometry.
• Spirally wound/random risers: describe other boiler types or coil designs, not this one.

Common Pitfalls:
Confusing with fire-tube boilers (gas inside tubes); assuming all water-tube boilers have vertical membrane walls only.

Final Answer: