The closed-cycle OTEC power plant was the first OTEC cycle proposed by D’Arsonval in 1881. This cycle uses a working fluid with a low-boiling point, usually propane or ammonia, in a closed flow path (Takahashi and Trenka, 1996). The working fluid is pumped into the evaporator where it is vaporized and in turn moves a turbine. Closed-cycle plants operate on a Rankine cycle. The first stage of this cycle is referred to as isentropic expansion, which occurs in the steam turbine. Isobaric heat rejection in the condenser follows. This stage the water vapor becomes a liquid and therefore the entropy is decreased. The next stage is the isentropic compression in the pump (Takahashi and Trenka, 1996). During this step, the temperature increases due to the higher pressure. The boiler then supplies isobaric heat causing the working fluid to vaporize. In an OTEC system the warm sea water would be pumped into the evaporator where the liquid ammonia would be pressurized. This pressure causes the ammonia to boil or become vapor. This works due to the ideal gas law that states that the temperature is directly proportional to the pressure; therefore if the pressure increases in a system, the temperature does too. The vapor ammonia then expands by traveling through a turbine. This turns the turbine making electricity. The ammonia vapor pressure at the outlet of the turbine is 7oC higher than the cold seawater temperature. The cold seawater is therefore brought up from the depths where heat exchange occurs and ammonia vapor is changed back into a liquid. The liquid ammonia is then pressurized by a pump started the cycle once more. Rankine cycles, in theory, are able to produce non-zero net power due to the fact that less energy is required to increase the pressure of a liquid then is able to be recovered when the same fluid expands as a vapor. It is for this reason that phase changes are essential when producing energy this way. The advantages of using a closed-cycle system are that it is more compact then an open-cycle system and can be designed to produce the same amount of power. The closed-cycle can also be designed using already existing turbo machinery and heat exchanger designs. [8] The operation of a closed-cycle OTEC plant, using anhydrous ammonia as the working fluid, is modeled with the saturated Rankine cycle. Fig. 4 shows a simplified flow diagram of the CC-OTEC cycle. The analysis of the cycle is straightforward.