It has been found that chlorofluorocarbon (CFCs) and hydrochlorofluorocarbon (HCFCs), which have been used since 1930, cause ozone layer depletion owing to their strong thermodynamics characteristics. Series of CFC and HCFC refrigerants have been regulated by the Montreal Protocol. Therefore, there is an urgent need to develop an alternative refrigerant to mitigate the problem of ozone layer depletion. This can be achieved in two ways: development of a new refrigerant and development of mixed refrigerants.
This study investigated the performance characteristics of ocean thermal energy conversion (OTEC) cycles when using existing mixed refrigerants for OTEC. Among the various available mixed refrigerants for industrial heat pumps, R32/R152a is used even in OTEC systems. For our simulations, R32/R152a was used in the existing closed cycle, regeneration cycle, and Kalina cycle, in which only ammonia and water are used as the mixed refrigerant.
The temperature of the warm heat source was kept at 26°C, and that of the cold heat source was kept at 5°C. The cycles were analyzed for R32/R152a at composition ratios of 100:0, 67:33, 50:50, 33:67, and 0:100.
Simulation results showed that the gross power of the closed cycle with just R32 was 22 kW, and efficiency of the cycle was 2.02%. When the mixed refrigerant R32/R152a was used in the ratio of 67:33, the gross power of the closed cycle was 23.24 kW, and cycle efficiency was 2.26%. Therefore, it can be seen that the gross power and cycle efficiency of R32/R152a increased by 5.6% and 11% from those of the existing single refrigerant. The same simulations were also conducted for a regeneration cycle and Kalina cycle with the same composition ratios of the mixed refrigerant. Therefore, the performance characteristics of OTEC cycles for various composition ratios of R32/R152a were verified.
