## 3 Results and Discussion  
### Model Validation  
At the first stage of the study, experimental measurements of the distribution of the air temperature and air velocity in the cross-sections of the test bench were carried out. These data were used to validate the numerical model. The inclined (\(-13^{\circ}\)) and horizontal positions of the bench were considered. Figure 6 shows theoretical curves and experimental points for the longitudinal component of the air flow velocity, while Figure 7 shows the theoretical curves and experimental points for the air flow temperature. The scenario considered had an HRR value equal to 14 kW and the angle of inclination of the channel was equal to \(0^{\circ}\). The measured parameter is marked along the X-axis, and the immersion depth of the sensor, measured from the upper wall of the flow area of the bench, is marked along the Y-axis. The temperature and flow velocity sensors were immersed down through holes in the upper wall of the channel, so the values along the Y-axis are given with a minus sign. The profiles were built for section No. 3 (near the exit from the channel) and section No. 2 (after the heat source). Considering that during the intense heating of the air flow, the measured values periodically changed over time (i.e., the distribution characteristics of the air flow were non-stationary); Figures 6 and 7 display not only the average values of the measured velocities and temperatures of the air flow, but also the minimum and maximum observed data values for a sample of measurement data at individual points. These are depicted using elements of the box-and-whisker plots. In addition to a zero-inclination angle, the case of an inclination angle of \(-13^{\circ}\) (downward air flow in the channel) was studied, and the fan performance was also varied. Figure 8 shows diagrams of the air velocity and temperature in section No. 3 (near the exit from the channel) for experimental points and numerically calculated curves. The HRR of the source was also set to 14 kW. A comparison of experimental and theoretical distributions of the air flow velocity and temperature was also carried out using other HRR values, but they were not included in this paper. Overall, the obtained data indicate good agreement between the numerical simulation and laboratory experiments at the considered channel inclination angles. Minor quantitative discrepancies between individual experimental points and numerical simulation data were observed, but overall, at a qualitative level, the model curves and experimental points demonstrated similar patterns of changes in air flow velocities and temperatures across the cross-section. The small discrepancies (less than 5%) were likely associated with errors in the measuring equipment, as well as inaccuracies in the selected mathematical model. These errors can arise due to simplifications in geometry (such as  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & \multicolumn{6}{c}{**Mass Flow at the Inlet**} \\ \cline{3-8}  & & & 0.5 kg/s & & 1 kg/s & & 2 kg/s \\ \hline
0.50 & \(0.65\cdot 10^{6}\) & 53.9 & — & 120.0 & — & 215.3 & — \\ \hline
0.40 & \(0.83\cdot 10^{6}\) & 46.8 & \(-13\) & 105.3 & \(-12\) & 187.2 & \(-13\) \\ \hline
0.30 & \(1.58\cdot 10^{6}\) & 48.3 & \(+3\) & 107.6 & \(+2\when creating boundary surfaces for the heater) and in physics (for example, the use of the RANS approach). Figure 6: Comparative analysis of calculated profiles and experimentally measured values of the longitudinal component of the air velocity in cross-sections No. 2 (**a**) and No. 3 (**b**). Figure 7: Comparative analysis of calculated profiles and experimentally measured values of the air temperature in cross-sections No. 2 (**a**) and No. 3 (**b**). In both considered sections, there was good agreement between the model and experimental data for the average values of velocity and temperature.