Question 39 OSE01 - Chief Engineer - OSV

The Correct Answer is C ### Explanation for Option C (-30°F) The problem requires determining the freezing protection limit based on the concentration of propylene glycol (PG) in a cooling water system, referencing a specific, unprovided illustration (MO-0209) which typically contains a concentration-vs-freezing point chart. Since the chart is missing, we must rely on standard conversion factors and concentration percentages used in such scenarios. **Step 1: Convert all volumes to a consistent unit.** * **System Capacity:** 10 gallons. * **Propylene Glycol Used:** 40 pints. We convert pints to gallons: $$1 \text{ gallon} = 8 \text{ pints}$$ $$\text{PG Volume} = \frac{40 \text{ pints}}{8 \text{ pints/gallon}} = 5 \text{ gallons}$$ **Step 2: Calculate the concentration percentage of propylene glycol (PG).** The concentration (by volume) is the volume of PG divided by the total system capacity: $$\text{PG Concentration} = \frac{\text{PG Volume}}{\text{Total Capacity}} \times 100\%$$ $$\text{PG Concentration} = \frac{5 \text{ gallons}}{10 \text{ gallons}} \times 100\% = 0.50 \times 100\% = 50\%$$ **Step 3: Determine the freezing point based on the 50% concentration.** Standard engineering tables and charts (like the hypothetical Illustration MO-0209) for a 50\% volume concentration of propylene glycol (mixed with water) typically indicate a freezing protection limit of approximately **$-30^\circ\text{F}$** (or $-34^\circ\text{C}$). Therefore, the limit of protection is $-30^\circ\text{F}$. --- ### Explanation of Incorrect Options **A) 10°F:** A freezing point of $10^\circ\text{F}$ corresponds to a very low concentration of antifreeze (typically less than 20% PG). Since the concentration calculated is 50%, this level of protection is too low. **B) -6°F:** A freezing point of $-6^\circ\text{F}$ corresponds to a concentration of approximately 30-35% propylene glycol. Since 50% PG was added, the actual protection is significantly greater than this value. **D) -53°F:** A freezing point of $-53^\circ\text{F}$ corresponds to a concentration of approximately 60% propylene glycol. Since the concentration calculated is exactly 50%, this level of protection is unattainable with the volume of PG used. (Note: $60\%$ concentration often represents the lowest practical freezing point achievable with PG, known as the eutectic point for some blends, but it requires more PG than was added.)