## 3 Results and Discussions
### Temperature and Pressure Characteristics  
The result of helium temperature and pressure characteristics is related to Section 3.1. As seen in Figure 3, the x-axis of the graph indicates the measuring time, while the y-axis shows the initial valve opening rate.  
Figure 2: Initial valve opening rate when charging helium gas in order of 20%, 60%, and 100%.  
This section describes the internal temperature and pressure results obtained from helium gas in a vessel at three different valve openings. As seen in Figure 3a, the temperature increased with a valve opening of 20% during 10 min because the helium gas was charged in a vessel. After 10 min, the temperature decreased due to the influence of the ambient temperature for 16 min. Additionally, it can be observed that temperature trends exhibit nonlinear characteristics when helium gas is compressed at higher flow rates.  
When the ventilation system is operating, the temperature undergoes a sharp decrease due to the orifice effect, resulting in a change of 7.5 degrees Celsius in the negative direction. As the temperature increases, the range from 20 \({}^{\circ}\)C to 49 \({}^{\circ}\)C shows a greater magnitude of change, and the maximum pressure recorded was 30 bar.  
It can be observed that pressure characteristics exhibit a linear relationship with temperature characteristics, allowing for direct comparison between the two. Namely, if the temperature increases, the pressure also increases. Specifically, it can be observed that the increase in pressure exhibits a linear relationship with time, likely due to the fact that the pressure does not change as much as the temperature. As seen in Figure 3b,c, the temperature and pressure values both increased up to 62 \({}^{\circ}\)C and 30 bar, respectively, when the valve was opened to 60%. The reason for the sudden increase in temperature is that  
Figure 3: Temperature and pressure characteristics as three different valve openings. (**a**) Temperature with 20% valve opening, (**b**) Temperature with 60% valve opening, (**c**) Temperature with 100% valve opening.  
the helium gas flow exceeded the orifice effects of the 20% valve opening control. It can be shown that at a valve opening of 100%, the temperature and pressure values significantly increased up to 84 \({}^{\circ}\)C and 30 bar, respectively, when compared to the other settings.  
Upon completion of the valve opening in the mass flow controller, it is observed that the pressure of helium gas instantaneously decreases and then increases. This phenomenon can be considered a challenge that may not be readily noticeable in facilities or measurement devices where all gases are typically charged. For instance, when filling natural gas, LPG, or propane gas into a reservoir, these errors may go unnoticed. In essence, it can be analyzed as a physical issue rather than a measurement problem, with the cause being more critical in situations requiring rapid and high-pressure charging. In the future, it appears that post-measurement technologies will be necessary to address these challenges, as indicated by the findings from this experiment.  
Consequently, both the temperature and pressure increase as the MFC valve opens further because the helium gas flow is accumulating during the valve opening time. Furthermore, in the case of helium temperature, it increases significantly when the gas is charged rapidly, compared to the pressure characteristics. The gas behavior principle as this increase in temperature and pressure becomes evident when the flow rate inside a constant volume vessel is rapidly compressed leads to an increase in particle collisions and internal energy changes within the helium gas.