A water cooled engine produces 1000 W of power.Water enters the engine block at 15 $\circ$ C and exits at 30 $\circ$ C.The rate of water flow is 100 L/hr.What is the engine's thermal efficiency?

Question

Quizplus · Accepted Answer

First, we need to calculate the heat absorbed by the engine, which can be done using the specific heat capacity of water and the change in temperature:

Q = (100 L/hr) x (1 kg/L) x (4.18 J/kg°C) x [(30°C) - (15°C)] 
Q = 15,750 J/hr

Next, we need to calculate the rate of energy input to the engine:

P_in = 1000 W

Finally, we can calculate the engine's thermal efficiency:

η = (P_out / P_in) x 100% 
η = (Q / P_in) x 100% 
η = (15,750 J/hr / 1000 W) x (1 hr/3600 s) x 100% 
η = 0.436 or 43.6%

Therefore, the closest answer choice is B) 36.4%.

A Water Cooled Engine Produces 1000 W of Power ∘\circ∘ C and Exits at 30

A Water Cooled Engine Produces 1000 W of Power $\circ$ C and Exits at 30