# Numerical Simulation of Co-Barrier Efficiency of Air Curtains in Mine Refuge Chambers
## 3 Simulation Results
### Effects of Installation Position and Jet Velocity  
To investigate the effects of air curtains with various installation positions and jet velocities on CO gas barrier performance, we used the pipeline air curtain with a hole diameter of 6 mm and a hole spacing of 15 mm. Through analyzing the numerical simulation results we get the best installation position of the air curtain and the law of the impact of jet velocity on the air curtain efficiency.  
Figure 8: Comparison of the experimental and numerical results.  
3.1.1. Installed the Air Curtain on the Left Side  
Figure 9 illustrates that installing air curtains can effectively barrier the CO gases getting into the transition room compared with no air curtain operation. The efficiency of the air curtain as a barrier for CO gas first rises and then falls as the jet velocity of the air curtain increases. The air curtain has the best barrier effect at a jet velocity of 18 m/s. At this time, the CO concentration in the transition room is 3100 ppm at 300 s.  
There is no air curtain functioning since the air curtain jet velocity is 0 m/s. Under the effect of thermal pressure, the CO concentration in the transition room increased rapidly to 7175 ppm within 90 s. After 90 s, the CO concentration in the transition room increased slowly, CO concentration reaches 8300 ppm at 300 s. As the door of the refuge chamber opens, under the action of hot pressing, a strong heat and mass exchange takes place between the outside environment and the transition room. We can see that the CO concentration in the transition chamber rises rapidly at the beginning of the simulation. After a period of time, the decrease in temperature difference leads to the decrease of heat and mass exchange rate, and the rising rate of CO in the transition chamber decreases, as Figure 10 shows.  
Figure 10: Cloud diagram of CO concentration in the transition room without air curtain at Y = 1.805 m.  
Figure 9: The CO concentration with air curtains installed on the left side.  
Increase the velocity of the air curtain jet from 6 to 16 m/s, the CO concentration curve slope gradually becomes smaller in the period of 0-90 s, and the efficiency of blocking CO gases gradually increases. A buoyant jet known as an air curtain blends the effects of forced and natural convection. Consequently, the air curtain requires to have enough kinetic energy to maintain the inside and outside the neutral plane pressure differences. The air curtain cannot form a complete airflow barrier from top to bottom owing to the low jet airflow energy. The jet airflow energy becomes higher due to the increased jet velocity, gradually forming a top-down airflow to barrier CO gases exchange. For this reason, the air curtain sealing effect becomes better. The air curtain jet velocity needs to be 18 m/s to have the best sealing effect, and the CO concentration in the transition room is 3100 ppm at 300 s. Currently, the CO concentration in the transition room varies as a straight line with time. The kinetic energy of air curtain flow increases with the increase of velocity. The high kinetic energy gas flow barrier makes the high concentration of CO gas under hot pressure enter the transition room at a specific rate. The efficiency of the air curtain to block CO gases decreases as the velocity increases to 22 m/s. Because the air jet velocity is too high, the kinetic energy of the airflow is too high, which makes the airflow hit the ground of the refuge chamber. Thus, CO gases accelerated to flow into the transition room. As a result, the air curtain barrier efficiency declines. The barrier performance of the air curtain is found to not be linearly related to the jet velocity based on the studies mentioned above.