Simple vertical boiler detail In a simple vertical boiler, the water tubes (cross tubes) are generally arranged as:

Introduction / Context:
The simple vertical boiler is a small, compact, fire-tube boiler. Many versions include one or more cross tubes through the furnace zone to increase heating surface and promote circulation. Understanding the orientation of these tubes helps visualize internal flow and heat transfer.

Given Data / Assumptions:

• Simple vertical (or vertical cross-tube) boiler configuration.
• Goal is improvement of natural circulation and heating surface without complex headers.
• Small-capacity, low-to-medium pressure application.

Concept / Approach:
Cross tubes are often placed with a slight inclination rather than perfectly horizontal. The incline encourages upward flow of hot water on the higher side and return of cooler water on the lower side, setting up natural circulation cells. The orientation also assists in draining and reduces sludge deposition compared with dead-level horizontal tubes.

Step-by-Step Solution:
Recognize the boiler type: fire-tube shell with a furnace and cross tubes.Assess circulation needs: inclined tubes enhance thermosyphon action.Conclude that “inclined” best describes the usual arrangement for cross tubes.

Verification / Alternative check:
Textbook schematics of vertical cross-tube boilers show one or two tubes pitched at an angle through the furnace and water space to encourage flow.

Why Other Options Are Wrong:
Perfectly horizontal tubes are less favorable for circulation and drainage; vertical tubes would convert the design toward a water-tube arrangement; “absent” is incorrect for cross-tube variants; spiral/helical is not typical for the simple vertical boiler.

Common Pitfalls:
Confusing the “simple vertical” with other vertical boilers that may not include cross tubes; assuming orientation has no effect on circulation.

Final Answer:
inclined