# Dependence of the Flue Gas Flow on the Setting of the Separation Baffle in the Flue Gas Tract
## 2 Materials and Methods
### PIV Measurement  
The CFD model was verified by PIV measurement. The experimental set-up consisted of the model with baffles created based on the CFD simulations, a closed air tunnel to ensure the flow conditions, and the equipment needed for the PIV method. The model of the flue gas tract was inserted into the fiberboard. This model was constructed from transparent polymethyl methacrylate (PMMA) material, which was connected using metal elements. The dimensions of the model were the same as when using the CFD, and the settings of the model were also modified in the same way. The closed air tunnel consisted of a flow fan, a differential pressure sensor for setting the fan operating velocity, a temperature sensor for controlling the flow conditions, an anemometer for measuring and setting the airflow velocity, a droplet generator that produced and distributed a tracer in the form of oil droplets to the air tunnel, and a logger. Oil droplets represented the particulate matter. The experimental set-up is shown in Figure 3.  
PIV equipment included a charge-coupled device (CCD) camera, a neodymium-doped yttrium aluminum garnet (Nd: YAG) laser, and the Dynamic Studio software for the evaluation measurements. Oil droplets were illuminated by the Nd: YAG laser. The main laser beam had a wavelength of 1064 nm, and the second laser beam with a wavelength of 532 nm was found in the spectrum of green light. The laser beam was transformed into a divergent laser light sheet by light sheet optics. The CCD camera recorded the figures at each pulse. This camera was rotated 90\({}^{\circ}\) from the laser plane and also equipped with a filter that let through only green particles. PIV equipment is shown in Figure 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Surface**} & **Boundary Condition** & \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**Value**} \\  & **Type** & & \\ \hline \multirow{3}{*}{Inlet} & Velocity inlet (setting 1) & & 0.298 \\ \cline{2-4}  & Velocity inlet (setting 2) & & 0.265 \\ \cline{2-4}  & Velocity inlet (setting 3) & & 0.251 \\ \hline Outlet & Pressure outlet & Pressure [Pa] & \(-\)12 \\ \hline - & Air density & Density [kg\(\cdot\)m\({}^{-3}\)] & 1.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Boundary conditions. The measurement was realized in a dark room without the influence of other light sources. The first measurement area was located at the top of the model, where the first baffle was curved. These measurements were realized with three different settings of the baffle. The second measurement area was realized in the place of the divide of the second baffle. The measurement realized in this area was only for setting 1. Before the start of the measurements, it was necessary to calibrate the camera and select points A and B. Based on these points, the scale was determined. The velocity of flowing oil droplets in the tunnels reached 2.5 m\(\cdot\)s\({}^{-1}\). The camera exposure time was set to 300 us. Depending on the flow velocity, the time between figures was also set to 450-900 us. The optimal displacement of the particles in the evaluation area should not be greater than 8 pixels. In this case, the maximum displacement was 6 pixels during the measurement between the two figures. The laser intensity should be adjusted so that the figure quality from the first laser and the second laser is the same. Based on the visibility of the particles and the number of shading and obstacle elements, the intensity of the first laser was set to 5.7-6.2 and the intensity of the second laser 6.0-6.3. Firstly, the size of the evaluated area was 16 \(\times\) 16 pixels. Then, if no particle was found, the area was gradually enlarged to 64 \(\times\) 64 pixels. The size of the evaluation area was determined so that all particles were recorded. The Dynamic Studio software (Dantec Dynamics A/S, Skovlunde, Denmark) used two figures from the measurement, the correlation, a mask, and the removal of erroneous vectors with the use of the range, peak, and moving average.