Ocean thermal energy conversion (OTEC) systems can convert the ocean thermal energy stored as a vertical temperature gradient in the ocean to electricity. Because the temperature difference in the heat engine is low, zeotropic mixtures and staging heat engines are applied to increase the power output. Recently, we proposed a method to evaluate the performance of the OTEC to identify the irreversible loss and energy conversion efficiency based on finite-time thermodynamics (FTT). In particular, this approach can determine the irreversible loss in the heat balance design and heat exchange process, and this concept can be extended to consider the internal irreversibility of heat engines. In this work, the performance of a single Rankine cycle OTEC with a crossflow plate heat exchanger as an evaporator and a condenser was experimentally evaluated to clarify the irreversibility of the heat engine and exergy. The internal irreversibility of the heat engine and effect of the staging of the heat engine were discussed. Moreover, the experimental results for the simple Rankine framework were extended to the numerical simulation of a two-stage Rankine cycle to compare the effect of the staging configuration such as cascade or parallel installations. The maximum net exergy efficiency reached 26%, 30% and 40% in the single Rankine cycle, parallel two-unit Rankine cycle and cascade double-stage Rankine cycle, respectively. The results demonstrate that the FTT model can effectively realize performance evaluation and can be applied to achieve optimal control and design.     «

Ocean thermal energy conversion (OTEC) systems can convert the ocean thermal energy stored as a vertical temperature gradient in the ocean to electricity. Because the temperature difference in the heat engine is low, zeotropic mixtures and staging heat engines are applied to increase the power output. Recently, we proposed a method to evaluate the performance of the OTEC to identify the irreversible loss and energy conversion efficiency based on finite-time thermodynamics (FTT). In particular, t...     »