## 3 Results  
Evaluation on the Underestimation Possibility of Inhalation Exposure by Zero-Dimensional Spray Model Based on CFD and Experiment Results  
The possibility of underestimation by the zero-dimensional spray model was confirmed in two steps. The first step was to evaluate the zero-dimensional spray model while verifying the validity of the CFD analysis based on the experimental results. In order to reflect the momentary aerosol spread assumption of the zero-dimensional spray model, the aerosol concentration over the total volume of space (far field) was calculated by using CFD, and the experimental results at six locations were averaged (far field). In the second step, in order to analyze the possibility of underestimation, the simulated concentration value and the experimental value at a specific location (near field) near the spray were compared with the zero-dimensional spray model results. The aerosol concentration of CFD was calculated over time by using the \(k-\varepsilon-\text{RNG}\) model, PSI-C method, DPM model and the pre-tested simulation conditions. The CFD simulation time is the same as the experiment and zero-dimensional spray model simulation time. The results of three methods were compared for 3600 s of physics/simulation. The aerosol from the spray was injected for 3 s in the three methods. The aerosol concentration of the zero-dimensional spray model was calculated by solving the ordinary differential equation for spray behavior. Figure 7a shows the comparison results for the three methods in the far field. As shown in Figure 7a, the spray model results, the experimental results in the far field and CFD in the far field show relatively good results compared to each other. After spraying, the aerosol concentration decreases rapidly within 5 min because the large-diameter particles quickly fall to the bottom. This phenomenon can be confirmed through the aerosol dynamic behavior result within 5 min by the CFD method in Figure 8a. After 5 min, the micro-diameter aerosol throughout the space is diluted throughout the entire space and removed through the upper outlet by ventilation. When the aerosol is sufficiently diluted, it can be seen that aerosols with small diameters are circulated throughout the space depending on the flow velocity field, shown in Figure 8b. Figure 7b represents the result of comparing the CFD result of aerosol concentration and the aerosol concentration measurement result in the near field with the result of the zero-dimensional spray model. Figure 7b shows that the CFD aerosol concentration results at a specific location and the experimental aerosol concentration values differ from that of the zero-dimensional spray model. This is a phenomenon caused by aerosol propagation, as shown in Figure 8a. The CFD results in the near field show similarity to the mean-max experimental results in near field over time. That is, the zero-dimensional spray model that ignores spatial characteristics can predict the results contrary to the actual exposure evaluation depending on the location, and the CFD method can explain the aerosol propagation caused by the actual turbulence well. In addition, Table 4 shows the exposure concentration of the time-weight average by the spray model, CFD modeling and experimental method. The spray model is underestimated by approximately five times when compared with the CFD results in the near field. We quantitatively show that the CFD results of exposure in the near field are similar to the measurement results in near field. Therefore, it can be seen that CFD and experimental methodologies, taking into account spatial characteristics, are needed for proper inhalation exposure assessment.