Question Bank • QB_FP_043 NAT • 2 Marks

Section 3: Farm Power

Farm Power

Subtopic: I.C. engine systems – fuel, cooling, lubrication, ignition, electrical, intake and exhaust

Question Statement:

A tractor diesel engine rejects $Q = 28.0\text{ kW}$ of heat to its liquid cooling system. Coolant enters the radiator at $T_{\text{in}} = 88^\circ\text{C}$ and exits at $T_{\text{out}} = 80^\circ\text{C}$. The specific heat capacity of the coolant is $c_p = 4.184\text{ kJ/(kg}\cdot\text{K)}$. The required mass circulation rate of coolant through the radiator in $\text{kg/min}$ is ________ (round off to 1 decimal place).

Answer Key:

50.2

Step-by-Step Solution & Explanation

1. Heat transfer rate equation: $Q = \dot{m} c_p \Delta T$ Where: • $Q = 28.0\text{ kW} = 28.0\text{ kJ/s}$ • $c_p = 4.184\text{ kJ/(kg}\cdot\text{K)}$ • $\Delta T = 88 - 80 = 8\text{ K}$ $\dot{m} = \frac{Q}{c_p \Delta T} = \frac{28.0}{4.184 \times 8} = \frac{28.0}{33.472} \approx 0.8365\text{ kg/s}$ 2. Mass flow rate in $\text{kg/min}$: $\dot{m}_{min} = 0.8365 \times 60 \approx 50.19\text{ kg/min} \approx 50.2\text{ kg/min}$
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