Question 38 OSE02 - Assistant Engineer - OSV

The Correct Answer is D **Explanation of why option D is correct:** 1. **Scale Deposits as Insulation:** Scale deposits (usually mineral deposits from the cooling water) act as thermal insulation. They form a layer between the hot exhaust gases (on the inside wall of the manifold) and the cooling water (in the jacket). 2. **Impact on Heat Transfer:** Because scale is an insulating material, its presence significantly increases the thermal resistance between the metal wall and the cooling medium. This reduction in conductivity leads to a **decrease in the overall heat transfer** rate from the exhaust gases to the cooling water. 3. **Impact on Wall Temperature:** If less heat is being effectively transferred away by the cooling water, the heat from the extremely hot exhaust gases builds up in the metal structure. Consequently, the temperature of the metal components, including the **inside wall of the exhaust manifold, will substantially rise**. This excessive temperature can lead to thermal stress, cracking, warping, and potential catastrophic failure of the manifold. **Explanation of why the other options are incorrect:** * **A) Excessive scale deposits would decrease heat transfer and lower the temperature of the inside wall of the exhaust manifold.** * This is incorrect because decreasing heat transfer means the heat is trapped, causing the wall temperature to rise, not lower. * **B) 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, which decreases (not increases) heat transfer. * **C) Excessive scale deposits would increase heat transfer and lower the temperature of the inside wall of the exhaust manifold.** * This is incorrect because scale decreases (not increases) heat transfer, and the temperature would rise (not lower).