Abstract
This study aims to design and optimize an organic Rankine cycle (ORC) and radial inflow turbine to recover waste heat from a polymer exchange membrane (PEM) fuel cell. ORCs can take advantage of low-quality waste heat sources. Developments in this area have seen previously unusable, small waste heat sources become available for exploitation. Hydrogen PEM fuel cells operate at low temperatures (70 °C) and are in used in a range of applications, for example, as a balancing or backup power source in renewable hydrogen plants. The efficiency of an ORC is significantly affected by the source temperature and the efficiency of the expander. In this case, a radial inflow turbine was selected due to the high efficiency in ORCs with high density fluids. Small scale radial inflow turbines are of particular interest for improving the efficiency of small-scale low temperature cycles. Turbines generally have higher efficiency than positive displacement expanders, which are typically used. In this study, the turbine design from the mean-line analysis is also validated against the computational fluid dynamic (CFD) simulations conducted on the optimized machine. For the fuel cell investigated in this study, with a 5 kW electrical output, a potential additional 0.7 kW could be generated through the use of the ORC. The ORC’s output represents a possible 14% increase in performance over the fuel cell without waste heat recovery (WHR).
Highlights
As the use of hydrogen for the storage and generation of electricity increases, new innovative methods to increase the efficiency of conversion between hydrogen gas and electricity will be needed
This work aims to show that an organic Rankine cycle (ORC) system can be designed to take advantage of the waste heat from a polymer exchange membrane (PEM) fuel cell and that an efficient expander can be designed for the selected fluid, operating conditions, and power output
This study focuses on the design of a radial inflow turbine under operating conditions in a waste heat recovery (WHR) cycle
Summary
As the use of hydrogen for the storage and generation of electricity increases, new innovative methods to increase the efficiency of conversion between hydrogen gas and electricity will be needed. This work aims to show that an ORC system can be designed to take advantage of the waste heat from a PEM fuel cell and that an efficient expander can be designed for the selected fluid, operating conditions, and power output. It is clear that low temperature waste heat could be a significant source of energy if it can be effectively exploited For this reason, low temperature ORCs are currently the focus of much research [23,24]. This study focuses on the efficiency and power generation of the ORC and the efficiency of the expander; future work will be required to design and optimize heat exchangers and pumps for the ORC that would enable an economic and a cost-benefit analysis for various designs before the system is implemented. A radial inflow turbine was chosen as the expander due to its higher isentropic efficiency
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