# Study on Thermal Radiation Characteristics and the Multi-Point Source Model of Hydrogen Jet Fire
## 2 Experimental Setup  
Figure 1 shows a schematic diagram of the experimental setup for the hydrogen jet fire experiments conducted in this study. This platform was designed to generate hydrogen jets under varying leakage diameters and pressures. The hydrogen purity used in the experiment was 99.999%. The hydrogen was stored in a cylinder of 12.5 MPa and introduced into a storage tank to provide a steadily varying hydrogen flow. The storage tank was a cylindrical container with a length of 60 cm and an outer diameter of 12 cm, with a hydrogen storage capacity of 7 L. It was made of 304 stainless steel and had a maximum pressure capacity of 15 MPa. The release pressure could be adjusted using a valve. The remote pressure gauge (LFT6200, LEFOO, Yueqing, China) ensured the hydrogen pressure in the storage tank was stabilized at 1 MPa before each experiment, and also monitored the pressure changes during hydrogen release. The release pressure at the leakage point was measured using the pressure gauge data. Nitrogen gas was used to purge residual gases in the storage tank before the experiment to prevent accidental combustion under flammable conditions. The ignition system consisted of a high-voltage pack and an ignition needle.  
The input voltage of the high-voltage package was 220 V, the output was 15 kV, and the distance between the two ends of the ignition needle head was 5 mm.  
During the experiments, hydrogen was released through stainless-steel nozzles with diameters of 1.2 mm, 1.5 mm, and 2.0 mm. A black background panel was placed behind the flame, and a digital camera (Canon EOS X5, Canon, Tokyo, Japan) was used to record the dynamic behavior of the hydrogen jet flames. The captured hydrogen jet flame images are shown in Figure 2. Using the MATLAB R2022b software, the color frames were converted into grayscale images to extract the flame length and width parameters. The maximum flame length and width of the hydrogen jet fire in the experiments were 0.9 m and 0.15 m, respectively. The jet fire experiments in this study aimed to obtain precise thermal radiation data at specific spatial locations, which are crucial for thermal radiation analysis and optimization model validation. The instantaneous thermal radiation from the hydrogen jet flames was measured using four radiometers. The radiometers were positioned along the axial direction of the flames on a vertical rail, at radial distances of 0.23 m and 0.50 m from the flame axis. The longitudinal positions of the four radiometers were 0.25 m, 0.50 m, 0.75 m, and 1.00 m, respectively.  
Figure 1: Schematic diagram of the experimental setup.  
Figure 2: Images of hydrogen jet fire.  
Considering the advantages of radiometers in terms of precise point measurements, high sensitivity, and reliability at high temperatures, a TS-34C heat radiometer manufactured by Captec, Lille, France, was selected for the experiment. These radiometers operated in the 0.3 to 50 \(\upmu\)m wavelength range, accurately measuring radiation in both the visible and infrared bands, with a response time of 50 ms and a sensitivity of less than 0.3 \(\upmu\)V\(\cdot\)W\({}^{-1}\cdot\)m\({}^{2}\). The output voltage signals from the radiometers and the remote pressure gauge were collected using a data acquisition device (JK360, Changzhou Jinailian Electronic Technology Co., Ltd., Changzhou, China). The voltage measurement range of the data acquisition device was 0.001 mV to 100 V, with a sampling frequency of up to 1000 Hz. By synchronizing the video footage captured by the camera with the data from the JK360, the dependence of the flame length, width, and thermal radiation on the leakage pressure under different conditions was obtained. Additionally, a portable gas detector was used to continuously monitor the hydrogen concentration in the environment during the experiments to prevent the accumulation of hydrogen to dangerous levels.