## 4 Results and Discussion
### Oxygen-Enriched Flow Characteristics and Oxygen-Enriched Area under Un-Air-Conditioned Conditions  
Figure 6 shows the maximum axial concentration distribution of oxygen with different oxygen supply flow rates in the single oxygen supply vent. When the axial distance gradually increases, the maximum axial oxygen concentration decreases; the axial concentration of oxygen decreases rapidly within a range of 0.55 m and then becomes close to the oxygen concentration in the environment. This is due to the convection diffusion process between pure oxygen and the surrounding air, with the difference in oxygen concentration as a driving force to mix oxygen quickly with indoor air.  
Figure 7 shows the distribution of oxygen mass fraction at the end of each time with the single oxygen supply process at a position 1.5 m above the ground. With the increase of the oxygen supply time, the oxygen-enriched area gradually expands, and the oxygen-enriched effect becomes more obvious.  
Figure 5: Comparing model results with experimental results in the oxygen-enriched area under un-air-conditioned conditions. (**a**) 1#, (**b**) 2#.  
Figure 6: Axial oxygen concentration distribution with a single oxygen supply vent for different oxygen flow rates: (**a**) \(\mathrm{D_{1}}\) = 0.006 m, (**b**) \(\mathrm{D_{2}}\) = 0.01 m.  
Figure 8 shows the oxygen-enriched area when the number of oxygen supply vents and the oxygen supply method are different under un-air-conditioned conditions at t = 120 s. With the different pipe diameters and different oxygen supply modes (in the form 1#, 2#, 3#, and 4#), the oxygen-enriched area varies widely. This is because when 3# is used for oxygen supply, after the oxygen is ejected from the oxygen supply vent at a certain outflow speed, the two gases meet, and the gas molecules directly collide with each other, making the flow velocity of the gas weaken. When the 4# is used for oxygen supply, the oxygen-enriched area formed by the double oxygen supply vents with a pipe diameter of 0.006 m roughly consists of two fan-shapes.  
Figure 9 shows the calculation of the oxygen-enriched area under different oxygen pipe diameters and different oxygen supply methods. It can be seen from Figure 9 that as the oxygen flow rate increases, the corresponding oxygen-enriched area also increases. The relationship between the oxygen-enriched area and the oxygen flow rate obtained by fitting  
Figure 8: Oxygen-enriched area with different oxygen supply vents and oxygen supply mode in un-air-conditioned state. (**a**) 1#, (**b**) 2#, 3#, 4# (D\({}_{1}\) = 0.006 m), (**c**) 2#, 3#, 4# (D\({}_{2}\) = 0.01 m).  
Figure 7: Oxygen mass fraction distribution of the single oxygen supply vent under un-air-conditioned conditions. (**a**) 5 s, (**b**) 20 s, (**c**) 60 s, (**d**) 90 s, (**e**) 120 s.  
is a linear relationship, as shown in Table 5. The oxygen-enriched area with a pipe diameter of 0.006 m is larger than that formed by a diameter of 0.01 m with the same oxygen flow rate. Therefore, the research will mainly study the oxygen supply pipe diameter of 0.006 m. It also can be seen that because the oxygen-enriched area of 2# and 3# is relatively small, the oxygen-enrichment effect is poor, so it is no longer considered 2# and 3#.