Question 31 UFIV01 - Chief Engineer - UFIV

The Correct Answer is B **Explanation for Option B (Correct Answer):** The rate of heat transfer ($Q$) is governed by the formula $Q = U \cdot A \cdot \Delta T$, where $U$ is the overall heat transfer coefficient, $A$ is the heat transfer area, and $\Delta T$ is the temperature difference. Installing fins on the firesides (the side exposed to hot combustion gases) of the water-tubes significantly increases the **effective heat transfer area ($A$)**. Since the fireside (gas side) heat transfer coefficient is usually much lower than the waterside coefficient, the fireside surface area is the limiting factor for heat absorption. By increasing the fireside area using fins, the overall rate of heat transfer from the hot gases to the water is substantially increased. **Explanation of Incorrect Options:** * **A) operating the boiler at less than normal water level:** Operating a boiler below the normal water level exposes tubes and surfaces meant to be cooled by water to overheating, potentially causing thermal damage and failure. While the remaining submerged area might experience a higher heat flux locally, the overall safe heat transfer rate is diminished, and boiler safety is compromised. * **C) increasing the amount of excess air to the burners:** Excess air dilutes the combustion gases, lowering the average flame and flue gas temperatures ($\Delta T$). Lower gas temperatures reduce the driving potential for heat transfer, thus decreasing, not increasing, the overall heat transfer rate and boiler efficiency. * **D) treating the boiler water with chemical oxygen scavengers:** Oxygen scavengers are used to remove dissolved oxygen from the boiler feedwater, preventing corrosion (pitting) of the internal surfaces. While essential for boiler longevity and safety, this chemical treatment does not directly or significantly increase the **rate** of heat transfer. The rate is determined by surface area, temperature differential, and cleanliness (lack of scale), not the presence of scavengers.