Chapter 16, Problem 44PP

Passage Problems

Power from the sea. Ocean thermal energy conversion is a process that uses the temperature difference between the warm surface water of tropical oceans and the cold deep-ocean water to run a heat engine. Figure 18.20 shows a typical decrease of temperature with depth below the surface in tropical oceans. In the heat engine, the warmer surface water vaporizes a low-boiling-point fluid, such as ammonia. The heat of vaporization of ammonia s 260 calig at 27°C, the surface-water temperature. The vapor is used to turn a turbine and is then condensed back into a liquid by means of cold water brought from deep below the surface through a large intake pipe A power plant producing 10 MW of useful power would require a cold-seawater flow rate of about 30.000 kg’s.

Figure 16.20

44 If the power plan: uses a Carnot cycle and the desired theoretical efficiency is 6 5%, from what depth must cold water be brought?

1. A.    100m
2. B.     400 m
3. C.     800 m
4. D.    Deeper than 1000 m