## 4 Conclusions  
Based on the experimental studies of flow structure in a vertical conical diffuser, the following conclusions can be formulated:  
1. An experimental setup was created to study various design methods for supplying air to a vertical diffuser under different initial conditions (flow characteristics). 2. Features of the flow structure in a vertical diffuser with a conventional air supply from below through one channel are as follows: - A pronounced central air flow is created in the diffuser along the vertical axis of the diffuser when using all channel configurations; - The shape of the cross-section of the supply channel has a significant impact on flow structure in a CD (round channel--stagnant zones in the corners; square channel--absence of stagnant zones; triangular channel--stagnant zones with a more uniform flow); - The main patterns of changes in the flow structure are preserved with an increase in air flow through the system from 0.02 to 0.067 m\({}^{3}\)/s. 3. Features of the flow structure in a vertical diffuser with nozzle air supply through four tubes at an angle of 45\({}^{\circ}\) include the following: - There are no stagnant zones or central flow in the diffuser; - The use of square and triangular nozzle tubes leads to a more uniform distribution of air flow throughout the entire volume of the vertical CD; - An increase in flow characteristics through the system contributes to a more uniform distribution of air flow throughout the entire volume of the diffuser (while the main patterns in the flow structure are preserved). 4. In terms of application, the following recommendations can be formulated: - The use of conventional air supply through one channel can lead to the creation of stagnant zones in the corners of the diffuser, which is typical of round and triangular cross-sections, and the use of a square supply channel causes a more uniform distribution of air throughout the entire volume of the diffuser; - Nozzle supply ensures the uniform distribution of air throughout the entire volume of the vertical diffuser with the creation of intense movement in the centre, which is most typical of round and triangular nozzle tubes, and the use of square nozzle tubes causes intense flow movement in the lower part of the diffuser, which quickly collapses upstream, thereby uniformly filling the entire volume of the cylindrical part of the diffuser;  
Figure 13: Thermograms of the flow structure in a vertical diffuser with nozzle air supply through tubes with different cross-sectional shapes (flow rate through the system \(q\) = 0.057 m\({}^{3}\)/s): (**a**) circle; (**b**) square; (**c**) triangle. Conventional air supply through one channel leads to a central flow along the axis of the vertical diffuser with the presence or absence of stagnant zones in the corners of the diffuser, and the nozzle air supply causes uniform distribution of air throughout the entire volume of the diffuser with the creation of an area of intense movement along the vertical axis. 5. According to the authors, the most suitable configurations of air supply to the vertical diffuser are profiled nozzle tubes for the installation for synthesis gas production. In these cases, stagnant zones are not formed in the diffuser, and the main flow has a shape close to the \"carrot\" (this is the optimal structure for the sawdust floating in the diffuser). 6. Areas for further research are related to obtaining detailed data on the gas dynamics of flow in a vertical diffuser with a hot-wire anemometer and/or PIV system, as well as studying the structure of flow in a two-stage conical diffuser. An additional line of research could be to study the effect of the inclination of the nozzle tubes on the gas dynamics and flow structure in a vertical CD. Conceptualisation, L.P.; methodology, L.P. and A.R. ; validation, L.P. and A.R. ; formal analysis, L.P. and A.R. ; investigation, L.P.; resources, L.P.; data curation, L.P.; writing--original draft preparation, L.P. and A.R. ; writing--review and editing, L.P.; visualisation, L.P. and A.R.