## 3 Experimental Facility  
A detailed configuration of the experimental facility is displayed in Figure 2a,b. The test configuration has four segments: the intake, pressure stabilization and temperature regulation, testing, and data measurement and processing systems. The intake system comprises an inverter and a 7.5 kW high-pressure fan, employing air as the working medium. The pressure stabilization and temperature regulation system includes two orifice flow indicators, pressure gauges, a temperature-controlled heater, and a resistance temperature detector (RTD). It is designed to precisely regulate the intake temperature and pressure at specified values. Moreover, the gas line system utilizes stainless steel piping with a diameter identical to that of the test section. This is conducted to eliminate the impact on test outcomes resulting from variables such as alterations in pipe diameter. The testing apparatus has a uniform heat distribution due to a continuous V-rib twisted tape, two pressure gauges, two RTDs, and several thermocouples. A constant heat flux was maintained in the system's copper tube. This tube was 1500 mm long, had a 60 mm inside diameter, and a 2 mm wall thickness. Its outside was wrapped with 0.7 mm diameter nichrome heating wire with a 46 \(\Omega\) resistance. The pipe surface was insulated to ensure uniform heat flux. Figure 2: _Cont._The external surface of the test section was sufficiently insulated to reduce heat loss to the environment. In addition, crucial steps were implemented to avert leaks from the system. In the experiment, the heat losses from the test section comprise around 3 to 7% of the overall heat supplied (\(Q=IV\)). The calm part was 1900 mm in length, which is approximately 31 times its interior diameter (31\(D\)). The calming part was employed to stabilize the entering air at a temperature of 25 \({}^{\circ}\)C. The temperatures of the inlet and outlet were recorded using T-type thermocouples and a data recorder. Fifteen T-type thermocouples were employed to measure the local wall temperatures of the test section. Each thermocouple was soldered in a V-groove within the test section wall (copper tube) and secured with thermal glue. Each V-groove cavity had a depth of 0.8 mm. To prevent the glued thermocouples from direct exposure to the heater, high-temperature silicon insulation was applied to the crevice following the soldering process. Fifteen T-type thermocouples were attached every 100 mm along the 1500 mm length of the tube, starting from the entrance of the test section at 50 mm (\(X_{1}\)) and continuing to 1450 mm (\(X_{15}\)), as shown in Figure 2b. The circumferential temperature variation turned out to be negligible after all T-type thermocouples were affixed to the tube's surface and placed around it. The T-type thermocouples' readings were used to calculate the mean wall temperature. Resistance Temperature Detectors (RTDs) were utilized to measure the temperatures of the fluid (air). The entry temperature (\(T_{i}\)) RTD was installed at the core section of the entry clam, while the outlet temperature (\(T_{o}\)) RTD was installed at the exit test section. The radial locations of the RTDs were varied (_r/D_ = 0.0, 0.15, 0.3, and 0.45). The average air temperature was determined by averaging the corresponding RTD values. The mean values of the inlet and outlet temperatures were obtained from two and four RTDs that were affixed at the entry and exit locations, respectively. The thermocouples were calibrated with a thermostat and were determined to have a precision of 0.1 \({}^{\circ}\)C. A data recorder (HIOKI LR8401, HIOKI, Tokyo, Japan, 10 ms high-speed sampling with 30 channels as standard) was employed to capture all temperature sensor signals produced by the system. All local surface temperatures were recorded once the system had attained a stable state. At least three repetitions of each experiment were conducted, and the wall and bulk fluid temperatures were recorded under steady-state conditions.