## 5 Results and Discussion  
### Case Comparison  
The performance of the IR-PCFC/GT system in all three configurations is first analyzed with methane fuel and under several nominal conditions. Steam to carbon ratio fed to anode is set at 2. The baseline values considered here are 33 A for the electrical current produced, 0.83 for the fuel utilization factor, 300 kW for the AC power consumption, 253 kW for the total energy input, and others as tabulated in Table 1.  
From Figure 5 and Table 3, it can be seen that PCFC temperature can significantly improve cell efficiency. Due to the increase in temperature, polarization losses decrease as the conductivity increases and the output voltage of the PCFC stack increases. In order to analyze better energy conservation and energy management in the hybrid system, all the system parameters are the same, and the thermal management effects on the system performance for higher power production with variation in the flow of GT fl  
Figure 4: Comparison between theoretical modeling results and experiment [36]. The green circle (\(\Circle\)), red triangle (\(\triangle\)), and blue square (\(\square\)) symbols are experimental data at temperatures of 1073 K, 1173 K, and 1273 K, respectively. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Stream**} & \multicolumn{3}{c}{**T (K)**} & \multicolumn{3}{c}{\(\dot{\text{E}}\text{x}^{\text{ph}}\) (**kW**)} & \multicolumn{3}{c}{\(\dot{\text{E}}\text{x}^{\text{ch}}\) (**kW**)} \\ \cline{2-10} \multicolumn{1}{c}{**Number**} & **Case 1** & **Case 2** & **Case 3** & **Case 1** & **Case 2** & **Case 3** & **Case 1** & **Case 2** & **Case 3** \\ \hline
1. & 426 & 426 & 426 & 187 & 187 & 187 & 7 & 7 & 7 \\  
& 627 & 635 & 537 & 257 & 266 & 164 & 86 & 86 & 86 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Stream properties (temperature, physical exergy flow, chemical exergy flow) in case 1, case 2, case 2, and case 3. Figure 5: Sankey diagram to show the exergy flow through the proposed IR-PCFC/GT hybrid system. In case 1, the heat of GT flue gas (at 1163 K) is used for heating the anode fuel preheater. To conserve energy, 76% of the fuel and air mixture flowing to the anode is preheated and mixed with the remaining 24% unheated fuel to attain the required temperature before entering the PCFC as shown in Figure 1. After the heat exchange in anode fuel preheating, the remaining thermal energy (at 955 K) is used for cathode air preheating. In fuel cells, exothermic chemical reactions increase the temperature of the PCFC stack. The PCFC temperature, power, and energy efficiency in case 1 are 965 K, 1208 kW, and 0.71, respectively. The functioning of the PCFC also depends on its operating temperature and gas inlet temperature. In case 2, the heat of GT flue gas (at 1422 K) is used for air preheating. The results show that the PCFC and GT power do not change as the fuel cell temperature, hydrogen generation, and the heat generated by combustion remain the same. Thus, recycling the GT flue gas to the preheater anode (HX1) or to the preheater cathode (HX2) does not affect the operating temperature and power generated by the fuel cell or turbine. In case 3, GT flue gas is proportionally used for HX1 and HX2. Figures 5 and 6 show that case 3 has a higher net power output than other cases. The outstanding performance of case 3 is related to its lower total exergy destruction. Installation of splitter (SPLTRI) after GT in case 3 is effective as it can reduce the exergy destruction due to mixing. In case 1, mixing the unheated fuel flow (No. 5a in Figure 1) and heated fuel flow (No. 5c in Figure 1) cause a decrease in exergy flow of 45.5 kW. In case 2, mixing the unheated fuel flow (No. 1c in Figure 2) and heated air flow (No. 1a in Figure 2) cause a decrease in exergy flow of 56.5 kW. In case 3, there is no exergy destruction due to mixing before entering the electrode inlets. So, exergy flow entering the fuel cell is higher along with higher physical exergy and operating temperature.