Organic Rankine cycle with liquid-flooded expansion and internal regeneration (ORCLFE) has been demonstrated leading to improvements in system efficiency with respect to conventional ORC with internal regeneration in the heat input temperature range from 80 degrees C to 200 degrees C. From a previous study [1], it was concluded that the selection of the positive displacement expander, the working fluid and its interaction with the flooding medium, and the two separate heat inputs heavily impacted the exergetic conversion efficiency of the cycle, but they were not analyzed in depth. In this paper, a more detailed thermodynamic cycle model has been developed to include a physical-based expander model to evaluate the impact of built-in volume ratio, flooding ratio, mechanical losses and the solubility of the working fluid into the lubricant oil. As waste heat recovery from 100 degrees C to 150 degrees C is the main application of the ORCLFE under investigation, low-GWP refrigerants such as R1234ze(Z), R1233zd(E) and R1336mzz(Z) have been considered as potential replacements of R245fa. A single-screw expander, which has been previously characterized, has been employed to optimize the ORCLFE at three heat source temperatures (100 degrees C, 120 degrees C and 150 degrees C) for each refrigerant, in order to obtain more realistic performance predictions. (C) 2017 Elsevier Ltd. All rights reserved.