Chapter 4.1, Problem 3P

A power plant produces 1 GW of electricity, at an efficiency of 40% (typical of today’s coal-fired plants).

(a) At what rate does this plant expel waste heat into its environment?

(b) Assume first that the cold reservoir for this plant is a river whose flow rate is $\text{1}00{\text{ m}}^{\text{3}}/\text{s}$. By how much will the temperature of the river increase?

(c) To avoid this “thermal pollution” of the river, the plant could instead be cooled by evaporation of river water. (This is more expensive but in some areas it is environmentally preferable.) At what rate must the water evaporate? What fraction of the river must be evaporated?