# Design Point Performance and Optimization of Humid Air Turbine Power Plants
## 4 Conclusions  
The parametric study of a humid air turbine system conducted in the current work has shown the high efficiency potential of this cycle across the design space, with a maximum thermal efficiency of 61.4%, achieved with maximum technology level of the heat exchangers and saturator, and maximum overall pressure ratio of at the gas generator. The absolute humidity at the inlet of the combustion chamber across the design space is within the limits for flame stability, never exceeding 0.25 kg\({}_{\mathrm{V}}\)/kg\({}_{\mathrm{a}}\).  
The final selection of the configuration of the power plant will depend on the levelized cost of the power production, which would require performing a full economic analysis. Depending on the market where the power plant is intended, an investment analysis should be conducted in order for the most appropriate candidate power system to be identified.  
The parameter that was found to primarily drive the thermal efficiency is the intercooler and recuperator effectiveness. For a change in intercooler effectiveness from 0.95 to 0.75, the thermal efficiency falls by 2 pp, whereas, for the recuperator, a change from 0.9 to 0.8 causes a reduction in thermal efficiency of 2.28 pp. Cycle efficiency is not significantly affected by aftercooler and economizer effectiveness.  
The parametric studies also showed that the technology level of each heat exchanger affects the thermal efficiency, total cost, and total weight of the power system differently: the recuperator was found to have the greatest impact on thermal efficiency, whereas the estimated acquisition cost is found to be mainly driven by the intercooler, while the total weight is mostly affected by the economizer and recuperator.  
Overall pressure ratio was found to have great impact over the cycle metrics; when the OPR becomes 30 from 40, the total cost of the heat exchangers increases by 10%, total weight by 5% while thermal efficiency is penalized by 0.67 pp. On the other hand, an increase of the saturator's pinch temperature difference \(\Delta T_{ps}\) to 15 K penalizes the thermal efficiency by 0.65 pp, while the full system's acquisition cost index was found to increase by 3%.  
Overall, a typical design space of a complex humid air turbine power plant was systematically explored and the dependencies between key cycle parameters and component design including weight and acquisition cost were identified. The impact of heat exchanger effectiveness on cycle metrics was demonstrated, revealing their influence on thermal efficiency, cost and weight that was not previously known. The outcomes of this research constitute a step forward in understanding the performance of a complex power system across its design space and appreciating the potential of such systems for applications where high efficiency combined with low overall plant volume and weight are of importance.  
This research program is financially supported by an Engineering and Physical Sciences Research Council (EPSRC) Industrial Cooperative Award in Science and Technology (I-CASE) Award and Rolls-Royce plc. (Bristol, UK) under the University Technology Centre in Aero System Design, Integration and Performance at Cranfield University (Cranfield, UK). The authors kindly thank Rolls-Royce plc. for permission to publish this work and for the technical support throughout the duration of the project.  
[PERSON]-d.-L. developed and implemented the heat exchanger and cycle design methodologies, [PERSON] developed the cycle thermal design and optimization platform, performed the simulations and analyzed the cycle performance data, [PERSON]-G. developed the heat exchanger detailed design and optimization framework, conducted the simulations and analyzed the design outcomes. [PERSON] put together the manuscript.  
The authors declare no conflict of interest.