A 1000 MW ( W) power plant is located next to a river and uses cooling water from the river to remove its waste heat. What is the resulting increase in river temperature? (The power plant has an overall efficiency of 33%. Assuming that all of the waste heat from the power plant is removed with cooling water and added to the adjacent river. The river flow rate is 100 m/s.
Solution: This problem is very similar to example 2.8, in that we are adding a specified amount of heat to a flow of water, and need to determine the resulting temperature rise. To solve, we first need to determine the amount of energy added. The power plant produces 1000 MW of electricity, but is only 33% efficient, meaning that it uses 3000 MW of fuel energy (). The heat energy added to the river is the amount that is not converted to electricity, or (3000-1000=2000 MW). We can now write our energy balance over the region of the river to which the heat is added. We will use to represent the temperature of the water upstream, and to represent the temperature after heating: