Liquid water enters an adiabatic piping system at 15°C at a rate of 8kg/s. If the water temperature rises by 0.2°C during flow due to friction, the rate of entropy generation in the pipe is?

23 W/K

Explanation:

Entropy of water at 15°C is 224.5 J/kg/K.

Entropy of water at 15.2°C is approximately 227.4 J/kg/K (interpolated).

The increase in entropy is therefore:

227.4 J/kg/K - 224.5 J/kg/K = 2.9 J/kg/K.

So the rate of entropy generation is:

2.9 J/kg/K * 8 kg/s = 23.2 W/K

Rounded to two significant figures, the rate is 23 W/K.