# Construction of a Numerical Model for Flow Flash Evaporation with Non-Condensable Gas
## 3 Results and Discussion
### Effect of Entrained CO\({}_{2}\) Concentration on Flash Performance  
The 63.5 \({}^{\circ}\)C water with four kinds of entrained CO\({}_{2}\) volume concentrations (1 vol%, 4 vol%, 7 vol%, and 10 vol%) was compared. The steam generation rate and CO\({}_{2}\) release rate after flash process stabilization are shown in Figure 6. Compared with pure water, the steam generation rate for water with entrained CO\({}_{2}\) increased by approximately 4.8%, 11.7%, 15.9%, and 20.0%, corresponding to volumes of 1%, 4%, 7%, and 10%, respectively. The increase in the steam generation rate is proportional to the increase in the steam-carrying volume. Compared with pure water, the presence of entrained CO\({}_{2}\) leads to an increase in the steam evaporation rate per step. In addition, the percentage of CO\({}_{2}\) components in the outlet steam of the flash chamber increased significantly with the inlet flow of entrained CO\({}_{2}\) and were approximately 0.13%, 0.50%, 0.84%, and 1.16%, respectively.  
The temperature, phase, CO\({}_{2}\) concentration, partial pressure, absolute pressure, and local steam production rate distribution are shown in Figure 7, under the 1 vol% entrained CO\({}_{2}\) volume concentration. As shown in Figure 7a, there is an area of high temperature above the inlet area, which is caused by non-condensable gas. Under the effect of gravity, the CO\({}_{2}\) entrained in the inlet water quickly floats upwards after entering the flash chamber and rapidly drives the water upwards, leading to an increase in water temperature above the inlet region. As can be seen from the distribution of local vapor generation rates in Figure 7, the regions of intense phase change include the low-pressure region at the top and  
Figure 5: Validation of the numerical model with experimental CO\({}_{2}\) release rate data: (**a**) schematic diagram of the experimental model Re-adapted with permission from Ref. [40]. 2013, Elsevier Ltd.; (**b**) comparison of the experimental and numerical results.  
Figure 6: Variation in the steam generation rate and CO\({}_{2}\) release rate of different entrained CO\({}_{2}\) volume fractions.  
the region near the inlet where carbon dioxide is present in large quantities. The increase in the flash steam generation rate was caused primarily by the high temperature and low water vapor partial pressure around the entrance of the flash chamber. The entrained CO2 gas in the flash chamber had little effect on the total pressure stratification phenomenon of the flash tank; however, the local high CO2 concentration reduced the partial pressure of the steam in the air space near the inlet. Under the combined effect of the low partial pressure of steam and the high temperature at the inlet, there was a severe flash area caused by entrained CO2 near the inlet area. Owing to the high steam generation rate in this area, the overall flash steam generation rate of the flash chamber also increased.  
The phase distribution and local CO2 release rate distribution are shown in Figures 8 and 9. Under the condition of a higher inlet entrained CO2 volume fraction, the phase-change process in the intense flash area is slightly changed because the increase in the inlet flow rate of entrained CO2 increased local CO2 concentration; however, the increase in the inlet flow rate also intensified the bubble uplift process, thus narrowing the area of the intense flashing area around the inlet. In general, the more inlet-entra  
Figure 7: Characteristic distribution of the flash chamber for the 1 vol% entrained CO2 volume fraction.  
region of the intense flash area, but increasing the intensity of the phase transition, and had little effect on the gas-liquid distribution.