Steam generation rate comparison: For a given size, the rate of flow of steam (steam-raising capacity per unit time) is generally __________ in fire-tube boilers compared with water-tube boilers.

Introduction / Context:
Boilers are broadly classified as fire-tube (hot gases in tubes, water outside) and water-tube (water/steam in tubes, hot gases outside). Their steam-raising rates differ due to heat-transfer area, water content, and permissible furnace rates.

Given Data / Assumptions:

• Like-for-like overall size comparison.
• Similar fuel and firing conditions.
• Standard design practices for safe operation.

Concept / Approach:
Water-tube boilers have many small-diameter water-filled tubes exposed to hot gases, yielding high heat-transfer area, rapid heat absorption, and lower water inventory. They can safely operate at higher pressures and respond quickly to load changes, giving higher steam-generation rates for a given size. Fire-tube boilers, with larger water content and fewer, larger gas tubes, raise steam more slowly and are suited to moderate rates.

Step-by-Step Solution:
Compare heat-transfer surfaces per unit volume: water-tube > fire-tube.Consider water inventory and response time: water-tube is quicker and supports higher steaming rates.Therefore, for the same size, steam flow rate of fire-tube boilers is less.Select “less” as the correct descriptor.

Verification / Alternative check:
Industry practice uses water-tube units for high-capacity, high-pressure power generation; fire-tube units serve smaller plants with lower steaming rates.

Why Other Options Are Wrong:
“More/the same/independent/unpredictable” ignore the fundamental geometry and heat-transfer differences that favor water-tube designs for higher rates.

Common Pitfalls:
Equating pressure capability with steaming rate without considering surface area-to-volume ratios and circulation characteristics.

Final Answer:
less