Performance analysis is performed for optimum design point of a closed-cycle Ocean. Thermal Energy Conversion (OTEC) system. Calculations are made for an OTEC model plant with a gross power of 100 MW, which was designed by the optimization method proposed by Uehara and Ikegami for the design conditions of 21° C ∼ 29° C warm sea water temperature and 4° C cold sea water temperature. Ammonia is used as working fluid. Plate type evaporator and condenser are used as heat exchangers. The length of the cold sea water pipe is 1000m. This model plant is a floating-type OTEC plant. The objective function of optimum design point is defined as the total heat transfer area of heat exchangers per the annual net power.
Ocean thermal energy conversion (OTEC) system of converting thermal energy is a into electricity by using the temperature difference between the warm sea water at the ocean's surface and the cold sea water of the depths. In the OTEC plant, the available temperature difference (15∼ 25° C) is small, and the thermal cycle efficiency is very small (2∼3%). which means that the heat transfer area of the heat exchanger per net power should be large in comparison with the one used in conventional thermal power plants or nuclear power plants (Uehara 1982). For the past few decades, a lot of research has been carried out on OTEC plant (Uehara et al. 1983, 1984, 1988, 1990) Small demonstration OTEC plants were constructed in America (Mini OTEC plant : 50kW) and in Japan (Tokunoshima plant : 50kW, Nauru plant : 100kW, Saga University plant: 75kW, Toyama plant : 3.5kW). Uehara and Ikegami (1990) developed the optimum design method of OTEC plant under given conditions of warm sea water temperature and cold sea water temperature. Using this method, the OTEC plant with maximum net power at minimum total heat exchanger area can be designed.
