## 2 Statement of the Research Problem and Measurement Tools
The main technical characteristics of the constant-temperature hot-wire anemometer are presented in Table 1. The analog signal from the sensor was fed to the analog-to-digital converter LCARD E14-300 (Moscow, Russia) for transformation into a digital code. The analog signal was recorded at a frequency of 3 kHz. Digital signals from the analog-to-digital converter were processed in specialized software LGraph2 version 2.35.20 (Moscow, Russia). The digital signal was visualized in real time and also stored in tabular form in the specified program. The data in tabular form could be exported to various programs for processing, analysis and visualization. Figure 3: Main elements of measuring system based on thermal anemometry method: 1—constant-temperature hot-wire anemometer; 2—analog-to-digital converter; 3—computer with specialized software; and 4—hot-wire anemometer sensors. The determination of experimental uncertainty in measuring instantaneous air flow velocities is based on taking into account the errors of the following devices: a barometer with an error of 0.1%, a thermocouple with an error of 1.0%, a micromanometer with an error of 2.5%. The relative uncertainty of air flow velocity measurement \(w\) was 4.8%. The uncertainty is given by taking into account the calibration error (1.1%) and then converting the analogue signal into a digital code (2.2%). The measuring system was regularly checked. The design of the single-thread constant-temperature hot-wire anemometer sensor and the method of its installation in the diffuser are shown in Figure 4. The sensor's sensitive element (thread) was made of tungsten and had a length of 4 mm and a diameter of 4 \(\mu\)m. The thread (sensitive element) of the sensor was positioned perpendicular to the incident flow. The sensor thread was located in the middle of the flat diffuser. The small dimensions of the sensor and sensitive element made it possible to avoid significant flow deformation in the measuring zone. The diameter of the ceramic insert in the sensor was 2 mm, the diameter of the holder was 0.5 mm and the diameter of the thread was 4 \(\mu\)m. One sensor was installed sequentially at each measuring point. Thus, the miniature dimensions of the sensor and the sensitive element did not introduce significant changes in the gas dynamics of the flow in the diffuser. The installation locations of the hot-wire anemometer sensors for measuring the air flow velocity in the diffuser are shown in Figure 5. The measurements were carried out in the diffuser section of the experimental setup (Figure 5). The first control section for height was located at a height of \(h\) = 50 mm from the inlet section of the diffuser. The distance between the sensors was \(l\) = 32 mm in this section. The distance between the sensors along the width of the diffuser starting from a height of 150 mm was \(l\) = 50 mm and the step in height was \(h\) = 100 mm. The distance from the extreme point to the wall was 10 mm at heights of \(h\) = 50 mm; 150 mm; 250 mm; 350 mm; and 550 mm (not shown in the diagram). \begin{table}
\begin{tabular}{c c} \hline \hline
**Hot-Wire anemometer Parameter** & **Quantitative Value of the Parameter** \\ \hline Power consumption, W & 5 \\ Output signal of the hot-wire anemometer channel, V & 0...5 \\ Absolute pressure value of the measured medium, kPa & 83.7...1600 \\ Average flow velocity measurement range, m/s & 0...100 \\ Frequency characteristics of the hot-wire anemometer & 10 \\ channel, kHz & 0...45 \\ Ambient air temperature, \({}^{\circ}\)C & 0...45 \\ Relative humidity, \% at a temperature of 35 \({}^{\circ}\)C & no more than 95\% \\ Barometric pressure, kPa & 84...106.7 \\ Overall dimensions, mm & 195 \(\times\) 100 \(\times\) 40 \\ Weight of the device, kg & 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The technical characteristics of the hot-wire anemometer.