Theoretical and experimental study on the secondary heat recovery cycle of the mixed working fluid in ocean thermal energy conversion

The small ocean temperature difference causes the power generation efficiency to not be high while the power generation cost is high; this method has not been commercially applied. Therefore, it is particularly important to find a new thermal cycle to improve the cycle efficiency. In this paper, a new cycle of the ocean temperature difference using a non-azeotropic mixed as working fluid is proposed, and a secondary heat recovery device is added to the solution branch separated by the separator. Theoretical analysis and numerical calculation were used to analyze the relationships between cycle efficiency and working fluid concentration, turbine inlet pressure and cold seawater temperature were obtained. The results show that the maximum cycle efficiency can reach 5.25% by adding a secondary heat recovery device. A 10 kW OTEC experimental system was constructed and analyzed; the system performance was obtained. The efficiency of the experimental system was found to be as high as 3.8%, while the experimental value of the test system was lower than the theoretical calculation value. Finally, the heat transfer coefficients of an evaporator and condenser under these conditions were obtained, which provides basic data and technical support for the engineering application of an OTEC plant.