## 3 Results and Discussion  
The previously suggested geometry and operational parameters of the COS hydrolysis reactor were used to evaluate its performance. In detail, concentration variation of COS and its conversion rate were compared to ascertain individual effects of the modeling parameters. For this, three levels of GHSV, length ratio, and temperature were selected for evaluation of operational and geometrical parameters, as listed in Table 4. Length ratio is a geometrical factor of the reactor tube and is defined by Equation (13). \[R_{length}=\frac{H_{cat}}{D_{cat}} \tag{13}\]  
All in all, effects of the reactor tube diameter and its length on overall performance were investigated under similar GHSV conditions. Figure 4 illustrates heat and fluid flow analysis results for reference modeling (GHSV = 1.0, length ratio = 1.0, Temperature = 573 K). Figure 4 depicts pressure distribution in the reactor, confirming the development of relatively high stagnant pressure at the catalyst area where the reactant gas mixture enters into the high resistance catalytic layer with high porosity. Figure 4 shows modeling result of the velocity field, showing the jet-type velocity distribution via the reactant gas mixture entering into the (reactor) tube inlet and then rapidly decreasing its velocity by uniform distribution among the catalytic pores. Figure 4 shows the temperature contour afforded by the external heat supply along the reactor tube wall surface, explaining reactor the gas temperature increase. The catalytic layer with a solid, high thermal conductivity area (porosity 0.4) enabled simultaneous heat convection and transfer, thus confirming high heat transport efficiency. Figure 5 schematically shows the modeling analysis result on reference model (GHSV = 1.0, length ratio = 1.0, Temperature = 573 K). More specifically, Figure 5 shows the concentration contour of reacting (COS, H\({}_{2}\)O) gases, highest concentration at the inlet of the catalytic layer, and gradual reduction in concentration with passage into the porous catalytic layer. The reactant flow is concentrated into the central portion of the catalytic layer by the inlet tube and renders a slow reaction rate caused by low thermal energy from the external heater. Reactant \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Condition** & **Value** & **Unit** \\ \hline \multirow{6}{*}{Inlet} & Velocity & 4.9–19.6 & m/s \\  & Temperature & 473 & K \\ \cline{2-4}  & & H\({}_{2}\) & 0.019 & - \\  & & CO & 0.675 & - \\  & & H\({}_{2}\)S & 0.573 \(\times\) 10\({}^{-3}\) & - \\  & Mass Fraction & COS & 0.880 \(\times\) 10\({}^{-4}\) & - \\  & & N\({}_{2}\) & 0.156 & - \\  & & H\({}_{2}\)O & 0.031 & - \\  & & CO\({}_{2}\) & 0.117 & - \\ \hline Outlet & Pressure Outlet & - & - \\ Wall & Constant Temperature & 543–603 & K \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Boundary conditions for numerical analysis. concentration is thus maintained at a high level, and this effect becomes insignificant with passage into the reaction area. On the other hand, H\({}_{2}\)S and CO\({}_{2}\) product gas concentration increases with passage into the catalytic reaction area. The reaction rate of the reactants renders a low concentration at the central region and this effect is gradually cancelled with passage into the outlet. Figure 5c graphically illustrates reactant concentration, products concentration, and temperature variation at the center of the reactor. The reactants' concentration rapidly decreases as they pass the reaction zone, while proportionately increasing the products' concentration. Equation (14) was used to evaluate reactor performance based on the concentration contour of COS gas at the inlet and outlet of the reactor. The catalytic conversion rate of COS is defined as the ratio of the concentrations of reacted COS to the originally supplied COS at the inlet of the reactor, and the COS conversion rate of the reference model is 41.1%.