## 3 Experimental Research Results, Analysis and Discussion
It should be noted that the gravitation of the main movement of the air flow is characteristic of all initial velocities under study except \(w_{\rm o}\) = 0.4 m/s. Velocity fields with their main movement along the right wall can have a negative effect on the uniformity of heat and mass exchange in the diffuser. This can lead to a deterioration in the mixing of working bodies in the flow gasifier and, accordingly, to a decrease in its efficiency and productivity. The flow turbulence intensity TI was calculated at each measurement point based on the instantaneous velocity data \(w_{x}\) and the TI fields in the vertical diffuser were obtained based on these calculations (Figure 9). Figure 8: Velocity fields \(w\) of stationary air flows in vertical conical diffuser for different initial velocities \(w_{\rm o}\): (**a**) \(w_{\rm o}\) = 0.4 m/s and (**b**) \(w_{\rm o}\) = 2.22 m/s. Figure 9: Turbulence intensity fields TI of stationary air flows in vertical conical diffuser for different initial velocities \(w_{\rm o}\): (**a**) \(w_{\rm o}\) = 1.12 m/s and (**b**) \(w_{\rm o}\) = 2.22 m/s. The following conclusions can be drawn from the analysis of Figure 9a:  
* a wide range of flow turbulence TI variation is observed from near-zero values to 0.9 in a vertical diffuser for a given initial flow velocity (\(w_{\rm o}\) = 1.12 m/s);
* there is an increase in TI along the downstream diffuser axis;
* the highest TI values are characteristic of areas near the side walls and along the diffuser axis in control sections along the diffuser height. It should be noted that the increase in the initial flow velocity \(w_{\rm o}\) causes a noticeable change in the turbulence intensity field in the diffuser (Figure 9b). The following conclusions can be made based on the analysis of Figure 9b:  
* the range of TI variation is from approximately zero values to 0.75 for \(w_{\rm o}\) = 2.22 m/s (accordingly, it can be stated that the flow turbulence decreases by an average of 15% in the diffuser with an increase in the initial velocity of the supplied air);
* the TI fields have a more uniform distribution over the entire volume of the diffuser for \(w_{\rm o}\) = 2.22 m/s compared to the fields for \(w_{\rm o}\) = 1.12 m/s;
* there is no correlation between the velocity fields and the TI fields for the two under consideration (comparison of Figures 8b and 9b);
* there is also an increase in TI along the downstream diffuser axis;
* the highest TI values are characteristic only of sections along the diffuser axis in the control sections along the diffuser height. It is known that TI characterizes the level of small-scale turbulence in the gas flow and affects the quality of the mixing of working media, the amount of heat transfer and the intensity of heat exchange in various technical devices [37; 38]. Accordingly, it can be assumed that the intensity fields of the flow turbulence in the vertical diffuser affect the efficiency of the flow gasifier and its productivity. The dependences of the change in TI along the height of the studied vertical diffuser along its axis for different initial flow velocities were obtained to analyze more detailed information about the gas-dynamic characteristics of the flow (Figure 10). Figure 10: The dependences of the turbulence intensity TI of a stationary air flow along the diffuser height \(h\) (along the diffuser axis) for different initial velocities \(w_{\rm o}\): 1—\(w_{\rm o}\) = 1.12 m/s; 2—\(w_{\rm o}\) = 1.75 m/s; and 3—\(w_{\rm o}\) = 2.22 m/s. Figure 10 demonstrates that the change in TI along the height \(h\) and along the diffuser axis is nonlinear. At the same time, the initial flow velocity at the diffuser inlet has a significant effect on the TI values, which is especially characteristic at heights \(h>350\) mm. An increase in the initial velocity leads to a slight decrease in TI for \(h<250\) mm. The differences in TI values do not exceed 8% for \(h\) up to 250 mm.