# Numerical Simulation of Co-Barrier Efficiency of Air Curtains in Mine Refuge Chambers
## 3 Simulation Results
### Effect of Structural Parameters  
Air curtains are installed on the top side of the refuge door, keeping the jet velocity constant at 22 m/s. Figures 13-15 illustrate the relationship between the CO concentration and the air curtain hole diameters of 4, 5, and 6 mm, and also their hole spacing of 10, 15, 20, 25, and 30 mm.  
Figure 12: The CO concentration with air curtains installed on the top side.  
Figure 14: The CO concentration in transition room with 5 mm hole diameters.  
Figure 13: The CO concentration in transition room with 4 mm hole diameters.  
Figure 15: The CO concentration in transition room with 6 mm hole diameters.  
Figures 13-15 demonstrate that when the air curtain hole spacing is increased while the hole diameter remains constant, the concentration of CO in the transition room rises over time. The 300 s transition room CO concentration exhibits a decreasing trend when the air curtain hole spacing remains constant and the air curtain hole diameter is increased. The total kinetic energy of the air curtain flow is proportional to the hole diameter when hole spacing, and jet velocity are both constant. In other words, the airflow barrier cannot form at the top and bottom because the total kinetic energy of the airflow ejected from the air curtain is lower for the smaller air curtain hole diameter. Thermal pressure causes the exchange of thermal mass between the outside environment and the transition room to aggravate, and this weakens the air curtain barrier effect. Increase the hole diameter and the total kinetic energy of the air curtain that is ejected will also rise. This will allow the air curtain to not only form a top-down airflow barrier but also to better withstand the effects of external thermal pressure as well, gradually increasing its barrier effect. The relationship between the ejected airflow kinetic energy and hole spacing, however, is inversely proportional when the air curtain hole diameter and jet velocity all are known. If the air curtain hole spacing is decreased, the total kinetic energy of the air curtain sprayed out of the curtain increases while its barrier effectiveness increases. Conversely, if the air curtain hole spacing is increased, the total kinetic energy of the air curtain sprayed out of the curtain decreases while its barrier effectiveness decreases.  
The red sphere represents the three-dimensional coordinates of hole diameter, hole spacing, and air curtain barrier efficiency. The mathematical relationship between air curtain efficiency and the three holes with diameters of 4, 5, and 6 mm and the five holes with spacings of 10, 15, 20, 25, and 30 mm is shown in Figure 16.  
\[Z=50.45-1.416x+11.92y \tag{12}\]  
In this formula, \(Z\) represents the barrier efficiency of air curtains, \(x\) represents the spacing between air curtain holes, and y for the diameter of the air curtain. It is discovered that the efficiency of the air curtain increases with increasing hole diameter and decreases with increasing air curtain hole spacing. The formula provides a reference for the optimal design of the air curtain pipeline structure.