## 3 Results of Numerical 2D Simulations and Discussion  
### Simulation of the Shape and Formation Time of the Air Curtain  
Figure 8 shows the formation of an air curtain in 15 s in the middle plane of the OTRDC with a single air curtain. It is seen from Figure 8 that the curtain is completely formed after 10 s. Figure 9 represents the formation of the air curtain in the middle plane of the refrigerated cabinet with the two-layer air curtain. The air curtain's full formation time is 7 s. Significant differences in the position of the air curtain in the refrigerated cabinet and the formation time are observed. The refrigerated cabinet with two air curtains has stronger airflow, and its radius is greater than that of the refrigerated cabinet with a single air curtain. The stronger airflow creates a stronger barrier to the ambient air. In this case, the warm air infiltration ratio is lower in the refrigerated cabinet with a two-layer air curtain.  
Figure 6: Comparison of the food temperatures obtained by CFD and experimentally.  
Figure 7: Comparison of the airflow velocities obtained by CFD and measurements.  
Figure 8: Distribution of the air velocity (m/s) in the middle plane of the OTRDC with a single air curtain.  
Figure 9: Distribution of the air velocity (m/s) in the middle plane of the OTRDC with the two-layer air curtain.  
Figures 10 and 11 present airflow velocities calculated for the scheme presented in Figure 5. It can be seen that in all measurement points, the air velocity is 0.05 to 0.2 m/s greater in the case of the cabinet with two air curtains. The second layer of the air curtain is faster and warmer than the first layer because a higher velocity of airflow generates a larger infiltration of ambient air in the second layer of the air curtain. The second layer of the air curtain is warmed faster but, in this case, reduces the ambient air infiltration into the first (main) layer of the air curtain. The air of the second layer escapes mainly into the environment and into the intake grille; the temperature, in this case, is lower than the case with the single air curtain.  
temperature for these packages. The M packages placed in the back are also affected by the environment, and the largest temperature difference is observed in the B1 package; in this case, the temperature difference is 1.19 \({}^{\circ}\)C (Figure 13). The average temperature of the M packages is 5.70 \({}^{\circ}\)C for the single air curtain and 5.12 \({}^{\circ}\)C for the two-layer air curtain. The infiltration ratio indicates how efficiently the air curtain works in the OTRDC. This can be computed according to the following formula:  
\[INR=\frac{T_{in}-T_{out}}{T_{air}-T_{out}}100\%, \tag{1}\]  
where \(T_{in}\) is the temperature of the intake air (RAG); \(T_{out}\) is the temperature of the outtake air (DAG or honeycomb); and \(T_{air}\) is the temperature of the surrounding air.  
For the single air curtain version, the infiltration is 10.4%, and in the case of the two-layer air curtain version, the infiltration ratio is reduced to 7%. The difference is 3.4%; therefore, the OTRDC with a two-layer air curtain works more efficiently, uses less  
Figure 12: Distribution of the temperature (\({}^{\circ}\)C) in the middle plane of the OTRDC with one air curtain (**left**) and two air curtains (**right**) after 24 h of the working cycle without defrosting process.  
Figure 13: Distribution of the temperature of food products in the middle plane of refrigerated cabinets (CFD simulation results).  
energy, and has better performance. The \(T_{aut}\) temperature for the two-layer air curtain was calculated as 80% of the first layer and 20% of the second layer temperature sum. This study utilized temperature and airflow velocity data obtained from previous experimental research. To enhance the performance of refrigerated cabinets, it is essential to optimize these parameters in future studies.