Question 45 AEL01 - Assistant Engineer - Limited

The Correct Answer is C. ### Explanation for Option C (-30 deg F) The problem asks for the freeze protection limit when 40 pints of propylene glycol (PG) are added to a 10-gallon cooling water system. To solve this, we must first determine the concentration (percentage) of PG in the mixture by volume, and then use the referenced illustration (MO-0209, which is a standard marine cooling system freeze protection chart for PG/water mixtures) to find the corresponding freeze point. 1. **Convert the volume of PG from pints to gallons:** * There are 8 pints in 1 US gallon. * Volume of PG in gallons = $40 \text{ pints} / 8 \text{ pints/gallon} = 5 \text{ gallons}$. 2. **Calculate the total volume of the system:** * Total volume (water + PG) = $10 \text{ gallons}$. 3. **Calculate the percentage concentration of PG by volume:** * Concentration $(\%) = (\text{Volume of PG} / \text{Total System Volume}) \times 100$ * Concentration $(\%) = (5 \text{ gallons} / 10 \text{ gallons}) \times 100$ * Concentration $(\%) = 0.5 \times 100 = 50\%$. 4. **Determine the freeze point using the chart (Illustration MO-0209):** * Standard charts for propylene glycol/water mixtures (such as MO-0209) show that a $\mathbf{50\%}$ concentration of propylene glycol provides protection down to approximately $\mathbf{-30^\circ\text{F}}$ (or $-34^\circ\text{C}$). Therefore, the limit of protection is $-30^\circ\text{F}$. ### Explanation of Why Other Options Are Incorrect **A) 10 deg F:** This temperature corresponds to a much lower PG concentration (usually around 15\% to 20\%). This level of protection would be insufficient for most operational areas requiring freeze protection. **B) -6 deg F:** This temperature corresponds to a PG concentration of approximately 35\% by volume. This is significantly less than the calculated 50\% concentration. **D) -53 deg F:** This level of protection requires a concentration significantly higher than 50\%, typically around 60\% to 70\% PG. Using a 50\% mixture provides protection to $-30^\circ\text{F}$, not $-53^\circ\text{F}$.