Multi-objective optimization of low temperature cooling water organic Rankine cycle using dual pinch point temperature difference technologies

The performances of organic Rankine cycle (ORC) systems are significantly varied by the heat source temperature and cold source temperature which are correlated and can be well indexed by dual pinch point temperature difference (PPTD). In this study, multi-objective optimization of net output power, total thermal conductance and expander size parameter of a low temperature cooling water ORC system using thirty-eight working fluids with different PPTDs was investigated and presented. The results show that the PPTD in evaporator is more sensitive to the net output power, total thermal conductance and expander size parameter than the PPTD in condenser. The alkane dry working fluid decane exhibits the best overall performance with net output power of 15.8 kW, total thermal conductance of 41 kW/K and expander size parameter of 0.101 mm, followed by nonane and carbon-11. For the low temperature cooling water ORC system with a heat source temperature of 100 °C, the optimal PPTD in evaporator is in the range of 5–7 °C (the optimal values for most working fluids are 5 °C), and the optimal PPTD in condenser is in the range of 6–9 °C (the optimal values for most working fluids are 6 °C).