## 3 Steam Condensing Performance  
The condenser is an important component of a thermal power plant; it receives and turns the exhausted steam from a turbine into water by basically cooling it. The main function of a condenser is to maintain a low back pressure on the exhaust side of the turbine allowing the turbine to do more work and to convert the discharge steam back to saturated-liquid water before it is pumped back to the steam generator. To accomplish these functions, the condenser must have a high cooling rate to fully remove the heat released due to condensation. In this section, we perform a simple calculation to see if the gaseous CO\({}_{2}\) or air is a better fluid for removing the heat released from steam condensation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multicolumn{2}{c}{**Container**} & \multicolumn{3}{c}{**T\({}_{\text{in}}\) and Mass Flux, \(\hat{m}^{\prime}\) (kg/m\({}^{2}\)-s), Entering a Cooling Device**} \\ \hline P & T & T\({}_{\text{in}}\) & & \(\hat{m}^{\prime}\) \\ \hline (MPa) & (K) & & (K) & & (kg/m\({}^{2}\)-s) \\ \hline  & & CO\({}_{2}\) & Air & CO\({}_{2}\) & Air \\ \hline
1.0 & 308 & 299 & 306 & 1265 & 1012 \\  & 313 & 304 & 311 & 1253 & 1003 \\
2.0 & 308 & 288 & 304 & 1871 & 1475 \\  & 313 & 294 & 309 & 1852 & 1462 \\
3.0 & 308 & 278 & 302 & 2354 & 1827 \\  & 313 & 284 & 307 & 2327 & 1812 \\
4.0 & 308 & 268 & 300 & 2781 & 2125 \\  & 313 & 275 & 306 & 2746 & 2106 \\
5.0 & 308 & 259 & 299 & 3176 & 2388 \\  & 313 & 266 & 304 & 3132 & 2367 \\ \hline \end{tabular}
\end{table}
Table 1: Temperature and mass flux, \(\hat{m}^{\prime}\) (kg/m\({}^{2}\)-s), of CO\({}_{2}\) and air entering a cooling device at MPa after being expanded from a high-pressure container.  
Figure 4: The Joule–Thomson coefficient of gaseous CO\({}_{2}\) and air as a function of the temperature and pressure before expansion, ((a): Joule-Thomson coefficient of CO\({}_{2}\) and air; (b): Ratio of the CO\({}_{2}\) Joule-Thomson coefficient to the air Joule-Thomson coefficient).  
A comprehensive analysis of a steam condenser is not be presented here. Here, we simply consider the problem involving the flow of the steam and of the cooling fluid in a two-flow-path condensation device. A vapor-saturated steam at 0.08 MPa and 41.5 \({}^{\circ}\)C is flowing in one flow path. In the other flow path, a cooler fluid (CO\({}_{2}\) or air) is flowing. Such a flow configuration is shown in Figure 5 as an example. For the steam, the temperature and the pressure are assumed to be constant. The pressure of the cold-flow path is also constant, but its temperature increases as it flows through the cold-flow path by absorbing the condensation heat released from the steam-flow path. As the steam flows through its flow path, condensation occurs and liquid water is produced; thus, the flow of steam is a two-phase vapor-liquid flow, where we assume that the velocity of the steam is constant. As the steam is condensed, the condenser pressure might decrease leading to an increase in the velocity as well as a decrease in the saturated temperature; these assumptions can be justified due to the fact that when the steam exits the turbine, it is distributed over a large area of short tubes (more than 20,000 tubes), and any effects due to steam condensation might not be significant. In addition, the main objective of the present work is to compare the effectiveness of dry air and CO\({}_{2}\) when they are used as cooling fluids, and since these assumptions are applied to both air and CO\({}_{2}\), they do not significantly alter the results of the present work. With these assumptions, the following equations are used (see [28]):