## 3 Numerical and Experimental Studies
### Experimental Study  
In this study, the effect of the pipe hole network on obscuration in the aspirating smoke detection system was investigated. For that purpose, the smoke flow through the pipe was considered. The pipe length was 20 m, and ten holes with a diameter of 5 mm were drilled in the pipe. The distance between every hole was 2 m. The ASD system with a smokebox and pipe is shown in Figure 2. The schematic diagram of the experiment was represented in Figure 3 and specifications of the experimental apparatus were represented in Table A1.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Hole**} & **Distance from Hole to ASD 1** & **Hole Diameter** & **Hole Distance** \\  & **(m)** & **(mm)** & **(m)** \\ \hline
1 & 2 & 5 & 2 \\
2 & 4 & 5 & 2 \\
3 & 6 & 5 & 2 \\
4 & 8 & 5 & 2 \\
5 & 10 & 5 & 2 \\
6 & 12 & 5 & 2 \\
7 & 14 & 5 & 2 \\
8 & 16 & 5 & 2 \\
9 & 18 & 5 & 2 \\
10 & 20 & 5 & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Case study for the straight pipe with ten holes.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Hole**} & **Distance from Hole to ASD 1** & **Hole Diameter** & **Hole Distance** \\  & **(m)** & **(mm)** & **(m)** \\ \hline
2 & 2 & 5 & 1 \\
3 & 3 & 5 & 1 \\
4 & 4 & 5 & 1 \\... &... &... &... \\
16 & 16 & 5 & 1 \\
17 & 17 & 5 & 1 \\
18 & 18 & 5 & 1 \\
19 & 19 & 5 & 1 \\
20 & 20 & 5 & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Case study for the straight pipe with twenty holes.  
The general operating principle of the ASD is shown in Figure 4. In the pipe hole network, the fan generates a vacuum which results in fresh air reaching the detector housing through the pipe holes. The smoke sensor is supplied with new airflow from the monitoring area. As the obscuration in ASD exceeds the setup value, the ASD triggers an alarm. The specification of the ASD system can be referred at [31].  
In this system, two pieces of aspirating smoke detection equipment were used. ASD 1 was connected directly to the straight pipe to measure the obscuration in the pipe, and ASD 2 was connected to the smokebox for monitoring the smokebox obscuration to maintain obscuration as constant. In the experiment, the smokebox obscuration was 5%/m, 10%/m, and 15%/m. For each respective smokebox obscuration, the location of the smokebox was changed from the first hole to the last hole to find the relation between fire source location and obscuration at ASD 1.  
In order to measure the obscuration in the aspirating smoke detection system, the pipe which had the hole was put into the smokebox, and the smoke moved from the smokebox through a pipe hole to ASD 1. At ASD 1, the obscuration was recorded and displayed on computer 1. The experiment was shown in Figures 11-13.  
Firstly, the fire was generated in the smokebox. After that, the obscuration in the smokebox was set up as 5%/m (controlled by ASD 2). Then, the smoke moved from the smokebox to ASD 1, so the value of obscuration at ASD 1 was recorded. The experiment at hole 1 was performed three times to obtain the accuracy value. After measuring with  
Figure 4: General operating principle of ASD.  
Figure 3: Schematic diagram of experiment used to determine the obscuration in aspirating smoke detection system.  
Figure 2: The aspiration smoke detection system with the smokebox and straight pipe.  
5%/m obscuration in the smokebox, the obscuration in the smokebox was changed from 5% to 10%/m, and 15%/m, respectively. The data at ASD 1 were re-recorded.  
Similarly, the location of the smokebox was changed from the first hole to the last hole. At every hole, the obscuration in the smokebox was set up as 5%, 10% and 15%/m, respectively.