Question 52 OSE01 - Chief Engineer - OSV

The Correct Answer is B **Explanation for Option B (Correct Answer):** Water-jacketed exhaust manifolds are designed to cool the exhaust gases and, crucially, the surrounding manifold walls by circulating cooling water through the jacket. Scale deposits (mineral buildup from the cooling water) act as thermal insulators. 1. **Impact on Heat Transfer:** Scale is a poor conductor of heat. Therefore, excessive scale deposits significantly **decrease heat transfer** from the hot manifold wall (where the exhaust gases are) to the cooling water in the jacket. 2. **Impact on Temperature:** Since the heat cannot be effectively transferred away by the cooling water, the heat generated by the exhaust gases builds up in the manifold material. Consequently, the temperature of the inside wall (the side exposed to the exhaust) of the exhaust manifold will **raise** significantly. This overheating can lead to material fatigue, cracking, and premature failure of the manifold. **Explanation of Incorrect Options:** * **A) Excessive scale deposits would increase heat transfer and raise the temperature of the inside wall of the exhaust manifold.** This is incorrect because scale acts as an insulator, thus **decreasing** heat transfer, not increasing it. * **C) Excessive scale deposits would decrease heat transfer and lower the temperature of the inside wall of the exhaust manifold.** This is incorrect. While scale does decrease heat transfer, the resulting thermal resistance causes heat to build up, leading to a **raise** in temperature, not a lowering. * **D) Excessive scale deposits would increase heat transfer and lower the temperature of the inside wall of the exhaust manifold.** This is incorrect on both counts. Scale decreases heat transfer and raises the wall temperature.