###### Abstract  
Vertical conical diffusers are used in power engineering, chemical industry, technological processes, and other industries. The efficiency of many machines and pieces of equipment is determined by the gas-dynamic and heat-exchange perfection of processes in diffusers. This study assesses the influence of the air supply method on flow structure in a diffuser. The studies were carried out on a test bench with thermal imaging for air flow rates ranging from 0.018 to 0.057 m\({}^{3}\)/s (42,500 \(<\) Re \(<\) 150,000). Two designs were examined: (1) a conventional air supply through one channel from below and (2) a nozzle air supply through four tubes at an angle of 45\({}^{\circ}\) to the vertical axis. In addition, the influence of the cross-sectional shape of the supply channels of both designs was studied. It is established that the use of a conventional air supply through one channel leads to the generation of a pronounced central flow along the vertical axis (all configurations of the supply channel) and the creation of stagnant zones in the corners of the diffuser (round and triangular channels; the use of a square supply channel causes the most uniform air distribution throughout the entire volume of the diffuser (while maintaining the central flow). It is found that with nozzle air supply, there are no stagnant zones in the corners and intense air movement generation in the centre of the diffuser (round and triangular tubes) can be observed; the use of square nozzle tubes causes intense flow movement at the base of the diffuser, which quickly collapses upstream, uniformly filling the entire volume of the diffuser's cylindrical part. The presented data can be useful for designing various machines and pieces of equipment with vertical conical diffusers. vertical diffuser; flow structure; stationary gas dynamics; supply channels; thermal imager; thermal imaging +
Footnote †: journal: Applied Physics Letters  
Presented below are the results of other authors studying physical processes in diffusers and data on the applied aspects of using CDs in various industries. Considerable work is being carried out to create models and algorithms for forecasting gas-dynamic characteristics in conical diffusers under various initial conditions [16; 17; 18; 19; 20]. For example, [PERSON] obtained original analytical equations for one-dimensional stationary flows in a conical diffuser [16]. The proposed solutions complement and expand theoretical knowledge about gas dynamics in CDs. [PERSON] and colleagues, using custom software, developed a mathematical model for forecasting the parameters of gas flows in a conical diffuser with an expansion angle of \(8^{\circ}\)[17]. The proposed model is highly accurate and is capable of estimating parameters for two-dimensional and three-dimensional flows. [PERSON] and [PERSON] conducted a focused study on creating a methodology for calculating a turbulent boundary layer in a conical diffuser [18]. Such techniques make it possible to determine with high accuracy the specific characteristics of CDs for specific applications. [PERSON] and co-authors created an automated algorithm for forecasting the gas dynamics of swirling flows in a conical diffuser based on machine learning technology [19]. The developed algorithm is capable of determining the flow parameters in CDs for stationary and non-stationary boundary conditions at the inlet. Studies have been conducted to develop methods for controlling the gas dynamics of flows in conical diffusers [21; 22; 23]. Thus, [PERSON] and others proposed a method for smoothing gas-dynamic unsteadiness associated with flow swirl in a conical diffuser by throttling the flow at the CD outlet [21]. An advantage of this method is that hydraulic resistance increases only slightly compared to other similar methods. [PERSON] and colleagues developed a method for controlling the flow in a CD with a ring vortex generator [22].