| Summary: | In order to successfully study the condensation and separation of a steam–CO<sub>2</sub> mixture, a boundary layer model was applied to the mixture condensation of steam and CO<sub>2</sub> on horizontal and vertical plates. The modified condensation boundary layer model of steam and CO<sub>2</sub>, given the CO<sub>2</sub> solubility in the condensate, was established, numerically solved, and verified with existing experimental data. Different condensation data of steam–air and steam–CO<sub>2</sub> mixtures were compared, and the effect of CO<sub>2</sub> solubility on the mixed gas condensation was analyzed under multiple pressure conditions (1 atm–10 MPa). The simulation data show that the presence of CO<sub>2</sub> will deteriorate the condensation heat transfer, just like air. Given that CO<sub>2</sub> is slightly soluble, some CO<sub>2</sub> can pass through the gas–liquid interface to enter the condensate film and reduce the accumulated CO<sub>2</sub> on the gas–liquid interface, which improves the condensation. However, the solubility of CO<sub>2</sub> is only significant under high-pressure conditions, inducing its effects on condensation. A comparison of the condensation coefficients of the steam–CO<sub>2</sub> mixture shows the lower impact of CO<sub>2</sub> condensation on the horizontal plate compared to that on the vertical plate. For most conditions, the steam–CO<sub>2</sub> mixture gas condensation heat transfer coefficient on the vertical plate surface is still larger than that on the horizontal plate surface, and the improvement in the condensation heat transfer coefficient caused by low CO<sub>2</sub> solubility (2 or 10%) at 10 MPa on the vertical plate is also larger than that of the horizontal plate.
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