# Design Point Performance and Optimization of Humid Air Turbine Power Plants
## 3 Results and Discussion  
A number of cycles have been selected to describe the effect of the \"design vector\" on the performance, cost and size of the power plant. The heat exchanger \"design vectors\" of the selected cycles (\(A\)\(\rightarrow\)\(G\)) are shown in Table 3 and Figure 3. When referring to the cycles in the text, the overall pressure ratio is defined by the superscript \(L^{OPR}\) and the pinch temperature difference in the saturator by the subscript \(L_{AT_{ps}}\).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & & **Units** & **Range** \\ \hline Intercooler, aftercooler, economizer effectiveness & \(\varepsilon=\ Q/Q_{max}\) & (-) & [0.75, 0.8, 0.95] \\ Recuperator effectiveness & \(\varepsilon=\ Q/Q_{max}\) & (-) & [0.8, 0.85, 0.9] \\ Saturator pinch temperature difference & \(\Delta T_{ps}\) & (K) & [5; 10; 15] \\ Overall pressure ratio & \(OPR\) & (-) & [30; 40] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Range of parameters across which the parametric study was conducted.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Design Variable** & & & **Range** \\ \hline Intercooler, Aftercooler, Economizer heat capacity ratio & \(C^{*}=C_{min}/C_{max}\) & [0.6–0.95] \\ Relative pressure ratio & \(relPR=\log_{OPR}PR_{LPC}\) & [0.25–0.75] \\ Saturator bypass & \(\beta\) & & [0–1] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Heat exchanger design parameters and range specification.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameter** & \(A\) & \(B\) & \(C\) & \(D\) & \(E\) & \(F\) & \(G\) \\ \hline \(\varepsilon_{IC}\) (-) & 0.95 & **0.85** & **0.75** & 0.95 & 0.95 & **0.75** & 0.95 \\ \(\varepsilon_{AC}\) (-) & 0.95 & **0.85** & **0.75** & **0.75** & 0.95 & 0.95 & 0.95 \\ \(\varepsilon_{The outcomes of the parametric cycle performance studies are analyzed using cycle \(A_{5}^{40}\) as a reference, which represents the system with maximum thermal efficiency, maximum effectiveness of all heat exchangers, maximum \(\mathit{OPR}\) and minimum pinch temperature difference in the humidifier. The design vector of the baseline cycle as well as its performance metrics are shown in Table 4. All values in subsequent plots are normalized against the cycle with maximum thermal efficiency \(A_{5}^{40}\).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Optimized Design Variable** & **Units** & **Value** \\ \hline Thermal efficiency & \(\eta_{HAT}\) & (\%) & 61.4 \\ Overall pressure ratio & \(\mathit{OPR}\) & (-) & 40 \\ Relative pressure ratio & \(\mathit{relPR}\) & (-) & 0.53 \\ Intercooler effectiveness & \(\varepsilon_{IC}\) & (-) & 0.95 \\ Aftercooler effectiveness & \(\varepsilon_{AC}\) & (-) & 0.95 \\ Economizer effectiveness & \(\varepsilon_{EC}\) & (-) & 0.95 \\ Saturator pinch temperature difference & \(\Delta T_{\text{ps}}\) & (K) & 5 \\ Recuperator effectiveness & \(\varepsilon_{REC}\) & (-) & 0.9 \\ Intercooler heat capacity ratio & \(C_{LC}^{s}\) & (-) & 0.95 \\ Aftercooler heat capacity ratio & \(C_{AC}^{s}\) & (-) & 0.95 \\ Economizer heat capacity ratio & \(C_{EC}^{s}\) & (-) & 0.82 \\ Saturator bypass & \(\beta\) & (-) & 0.43 \\ GT inlet gas mass flow & \(\dot{m}_{g,GT\ inlet}\) & (kg/s) & 40.6 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Design variables values of the baseline cycle \(A_{5}^{40}\) with maximum thermal efficiency.  
Figure 3: Cycle thermal efficiency across the design space as a function of the heat exchanger effectiveness—\(\mathit{OPR}\) = 40 & \(\Delta T_{\text{ps}}\) = 5 K.