The characteristics of an Ocean Thermal Energy Conversion! (OTEC) System using nonazeotropic binary mixtures HCFC22 + CFC114 and HCFC22 + HFC134a have been studied with numerical simulation. The calculation conditions are following: generated power 1OOMW, warm seawater temperature 28°C, cold seawater temperature 7°C, length of cold seawater pipe 800m. Although the thermal efficiency of the OTEC cycle is improved by using binary mixtures, the heat transfer area per net power output is not decreased because the heat transfer coefficient of binary mixtures is lower than that of pure working fluids, therefore, the heat transfer area becomes larger for the binary working fluids than for the pure working fluids.
Nonazeotropic binary mixtures have gained extensive interest as a working fluid of the power cycle operated with small temperature differences, and a heat pump and refrigeration cycle. An advantage of the binary mixtures is the possibility of improving the thermal "efficiency of the cycles by using the sliding temperature during condensation and evaporation processes in counterflow type heat exchanges. Marston(1990) carried out a parametric analysis of the Kalina cycle (KaIina,1984) which utilizes a mixture of ammonia and water as the working fluid, and the potential for combined cycle power plant efficiencies was shown to be good or better than advanced energy conversion technologies. Although the characteristics of the power cycle using the binary mixture have been little studied, those of the heat pump cycle have been studied experimentally and numerically by many researchers, Arora(1967), Jakobs and Kruse(1979), Stoecker and Walukas(1981), Fujii et aI.(1987), McLinden and Radermacher(1987), Miyara et aI.(in printing). Miyara et aI.(1992) pointed out that the conditions of the heat sink/source fluid and the performance of the heat exchangers must be considered to estimate the heat pump cycle performance.