This experiment shows that heated water expands a working medium (the air inside the bottle) and makes it do “work” (blow up the balloon slightly). Cold water restores the medium to its original volume so that it can work again when reheated.

     The experiment also demonstrates the principle of opera- tion of a real ocean thermal energy conversion system: The heated liquid turns into an expanding gas, which “works” by turning the turbine. When cooled, the gas condenses back into a liquid, shrinking in volume.