6. A water brake copupled to an engine on test absorbs 70 kW of power. Find the heat generated at the brake per minute and the mass flow of fresh water through the brake, in kg/min if the temperature increase of the water is 100 C. Assume all the heat generated is carried away by the cooling water

4200 kJ

10 kg/min

Explanation:

70 kW means 70 kJ per second. So in a minute, the amount of heat generated at the brake is:

70 kJ/s * 60 s/min = 4200 kJ

Heat = mass * specific heat capacity * increase in temperature

4200 kJ = m * 4.184 kJ/kg/C * 100 C

m = 10 kg

So every minute, 10 kg of water is heated. So the mass flow is 10 kg/min.