Performance enhancement of the combined power-refrigeration cycle using a liquid-gas-gas ejector for ocean thermal energy conversion

Abstract

The practical implementation of ocean thermal energy conversion technology faces constraints due to the low temperature differentials, resulting in limited energy conversion efficiency. This research introduces a novel combined power-refrigeration cycle that utilizes a hybrid liquid-gas-gas ejector to amplify the conversion efficiency. The gas extracted from the turbine is employed as auxiliary fluid within the liquid-gas-gas nozzle, effectively countering the low ejection coefficient associated with conventional liquid-gas ejectors. To elucidate the mechanism behind the liquid-gas-gas ejection process involving an ammonia-water-based absorption working fluid, a comprehensive fluid flow model for ejector is developed. This model facilitates the clarification of the non-equilibrium phase transition process occurring within the ejector. Parametric analysis was conducted to assess cycle performance under various operating conditions. The results show the innovative cycle can attain power/refrigeration efficiencies of 1.58 %/17.45 % while maintaining a refrigeration temperature of −18 °C. Performance comparisons indicate that the proposed liquid-gas-gas ejector based cycle reduces the minimum refrigeration temperature by 20.5 % in contrast to the cycle employing only the liquid-gas ejector, all while preserving power output. Furthermore, despite a mere 26 °C temperature difference, the refrigeration capacity of this cycle significantly outperforms those operating at greater temperature differentials. These findings demonstrate a substantial enhancement in the refrigeration and power capabilities of ocean thermal energy conversion.