Thermal Performance Analysis of a High-Efficiency Ocean Thermal Energy Conversion System Utilizing a Proposed Power Cycle

Ocean thermal energy provides an eco-friendly and sustainable clean energy source; however, low system efficiency impedes the commercial application of ocean thermal energy conversion (OTEC). The present research proposes an OTEC cycle, which uses an ammonia-water mixture as a working fluid, and improves the thermal efficiency and net output of the OTEC system by recovering and using surplus heat based on regeneration and a vapor extraction mode. To evaluate the performance of the proposed cycle, the thermal model of the cycle was established based on the energy conservation and the laws of thermodynamics and by analyzing the cycle process. In addition, a performance comparison between the proposed cycle and the basic OTEC-Rankine cycle was performed. The results show that the mass fraction of working fluid, turbine inlet pressure, and cold and heat source temperatures affect the thermal cycle performance. With an increase in turbine inlet pressure, both the thermal cycle efficiency and net output increase initially and later drastically decrease under the same cold and heat source temperature. As a result, the highest efficiency and maximum net output are achieved under the corresponding optimal pressure. The thermal efficiency and net power output of the proposed cycle (5.5% and 8.19 kW) are both evidently higher than the Rankine cycle (4.6% and 6.47 kW) under uniform conditions.