Subtopic: I.C. engine systems – fuel, cooling, lubrication, ignition, electrical, intake and exhaust
Question Statement:
In a pressurized liquid cooling system of a modern farm tractor, the radiator pressure cap maintains a positive gauge pressure of approximately $0.5\text{--}1.0\text{ bar}$. The primary thermodynamic purpose of this pressurization is to:
Options:
(A) Lower the freezing point of the cooling water below $-10^\circ\text{C}$
(B) Raise the boiling point of the coolant to $110\text{--}120^\circ\text{C}$, preventing boiling and cavitation under heavy draft loads
(C) Increase water pump rotational speed
(D) Facilitate rapid chemical breakdown of rust deposits
Answer Key:
B
Step-by-Step Solution & Explanation
- According to the Clausius-Clapeyron relation, saturation temperature increases with saturation pressure.
- Pressurizing the cooling system to $\approx 0.7\text{--}1.0\text{ bar}$ raises the boiling point of water from $100^\circ\text{C}$ to $\approx 115\text{--}120^\circ\text{C}$.
- This permits higher operating temperatures (improving engine thermal efficiency) and prevents boiling over during intense field plowing on hot summer days.