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Session: Working fluids I
Session starts: Tuesday 08 October, 11:20
Presentation starts: 12:20
Room: Willem Burger Zaal

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Baolin An ()
Yuanyuan Duan ()
Zhen Yang ()

Abstract:
The utilization of low-to-medium temperature heat sources is great importance for efficient energy utilization. Low-to-medium temperature heat sources can not be used with water based cycles due to their low efficiencies. The organic Rankine cycle (ORC) using organic fluid as the working fluid can make better use of these heat sources. HCs have low GWP and good thermal performance but high flammability. ORCs using HCs are mostly subcritical cycles that always have large heat transfer temperature differences. The natural working fluid CO2 is non-flammable, but has poor efficiencies and high operating pressures. The mixtures of CO2/HCs may have good thermal performance and low flammability. This study analyzed the thermal efficiencies, exergy efficiencies and system power outputs of ORC with CO2/ethane, CO2/propylene, CO2/propane, CO2/isobutane and CO2/cyclopentane mixtures. The CO2 molar fractions in these mixtures were varied from 0 to 100. The systems were assumed to be connected to geothermal, engine exhaust or cement kiln exhaust heat source, with a geothermal source temperature of 393.15 K, an engine exhaust temperature of 523.15 K and a cement kiln exhaust temperature of 603.15 K. The 50% CO2 and 50% HCs molar fraction mixtures were selected to analyze the correlations between the thermal efficiencies, exergy efficiencies and system power outputs with the peak cycle pressures. The concept of pure fuel minimum ignition energy was extended to the mixtures to analyze the flammability, and the CO2/propane minimum ignition energy was calculated.