Forced-Circulation Steam Boilers — Purpose of the Applied Force In a forced circulation steam boiler, for what purpose is external mechanical force (via pump) applied to the working fluid?

Introduction / Context:
Boilers can operate with natural circulation (density difference driven) or forced circulation (pump driven). Understanding the purpose of the pump in a forced-circulation arrangement is fundamental to appreciating modern high-pressure boiler design, heat flux control, and reliability.

Given Data / Assumptions:

• High-pressure steam generator with a circulation pump.
• Water/steam mixture flows through furnace walls, risers, and downcomers.
• Goal is to maintain adequate mass flow past heat-absorbing surfaces.

Concept / Approach:
In forced circulation, a pump imposes a specified flow rate through the evaporator circuit. This stabilises heat transfer, prevents local film boiling, improves temperature uniformity, and enables higher heat fluxes and pressures than those sustainable by natural circulation alone. The pump is not primarily for “drawing” or “draining” water; its function is to circulate water (and wet steam) through the heating surfaces continuously and reliably.

Step-by-Step Solution:
Identify main objective: maintain adequate coolant flow across high heat-flux regions.Map role of pump: create and control circuit circulation independent of buoyancy.Conclude that the applied force is for circulation.

Verification / Alternative check:
Design guidelines specify minimum circulation ratios to avoid tube overheating; pumps are selected to meet these targets.

Why Other Options Are Wrong:
to draw water: vague and not the principal purpose.to drain off the water: draining is a maintenance operation, not continuous boiler operation.all of these: incorrect because only circulation is correct in normal service.

Common Pitfalls:
Assuming natural circulation suffices at very high pressures; buoyancy reduces as density difference shrinks.

Final Answer:
to circulate water