Modelling and optimization of organic rankine cycle for waste heat recovery in marine engines.

In this thesis, a thermodynamic analysis and optimization is conducted for marine applications with a strong focus on the working fluid selection, different cycle configurations (basic/recuperated) and the effect of seawater temperature variation on the performance of system. The thermodynamic model is created which simulates the ORC operation at different heat source conditions for various type of working fluids and optimization is done maximizing net power output as the main objective. A prescreening procedure is applied first to select desired working fluids at specific heat source conditions. This procedure was based on GWP&ODP, condensation pressure and Jacob numbers. The findings demonstrate that at each heat source temperature, the best performing working fluid is different, which emphasizes the importance of working fluid selection, as it has to be matched with the heat source temperature. In addition, the variations in the seawater temperature effect the system as the seawater temperature increases 10 oC, the net power is reduced 26.8% in some cases with an increase in condensation temperature and pressure. Study also revealed that whereas at low temperatures simple configurations perform better, at higher heat source temperatures, the benefits of using recuperator become more significant. Furthermore, variations in seawater temperature were also found to have a direct impact on cooling water flow rate and therefore, ORC efficiency and net power output. Lower cooling water demand at higher seawater temperatures reduced the cooling pump power consumption but at the cost of reduced ORC net power output. The comparison between the auxiliary power consumption and ORC efficiency indicates that there is a need for cooling system operation optimization. Future work should include experimental validation, techno-economic evaluations and adaptive cooling strategies to enhance the system efficiency in a dynamic marine condition.