Performance of a simple Rankine cycle with various working fluids for OTEC applications

Dongsoo Jung, Ho-Saeng Lee, Hyeon-Ju Kim
Inha University, Korea

Keywords: Working fluids, OTEC, global warming, ozone depletion

In this paper, performance of various working fluids is evaluated for the closed OTEC power plants operating on a simple Rankine cycle. In selecting working fluids in OTEC plants, not only the efficiency but also environmental properties of the fluids are to be considered carefully. Seven pure fluids of R22, R134a, R717, R290, R1270, R1234yf, and R32 and three mixed fluids of R32/R1234yf, R32/R134a, and R32/R152a are used in the analysis. Results show that R717 has the highest cycle efficiency among the pure fluids considered. Due to toxicity, however, it would be the last candidate to be used in the actual OTEC plants. R22 and R32 have the slight efficiency decrease of 3% as compared to R717. R22, however, can’t be used due to ozone depletion potential. R32 is a good candidate since its global warming potential is reasonably low and it also provides high vapor pressure resulting in the reduction of the OTEC plants. Non-azeotropic mixtures of R32/R152a, and R32/R1234yf show slightly better efficiency than that of R717. When counter-current boiler and condenser are used in the OTEC plants, these mixtures will be good long term candidates since their efficiency and environmental properties are very good.

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