Zhangmao Hu

With the safety and reliability of the electrical equipment used in information systems becoming more important, prefabricated fire-extinguishing devices using heptafluoropropane as the extinguishing agent have broad application prospects. However, few studies have focused on the vaporization performance of heptafluoropropane in the context of fire suppression and the safe distance for electrical equipment. This study proposes a numerical simulation model to analyze the vaporization and cooling performance of sprayed heptafluoropropane. First, experimental measurements with no fire source are performed to verify the numerical model. Through numerical and experimental methods, the temperature, concentration, and velocity distribution of the sprayed heptafluoropropane are analyzed to improve its vaporization performance and determine the safe distance. Finally, heptafluoropropane spraying with a fire source is simulated, allowing for the discussion of its cooling effect and fire-extinguishing performance. The results illustrate that the mass ratio of liquid and gas phases in the sprayed heptafluoropropane are 20.2% and 79.8%, respectively. Heptafluoropropane spraying reduced the average temperature in the protective room, with the final value reaching 270 K. The mass fraction of the heptafluoropropane maintained a value of 0.1 at a distance of 0.8 m in front of the nozzle axis. The main findings of this research indicate the temperature variation and fluid flow performance associated with heptafluoropropane spraying, as well as providing a reference value for a safe distance from the nozzle.

Energy utilization of the large amount of biowastes is of great significance to environment protection and energy supply. This study investigated the co-combustion behavior and kinetics of traditional Chinese medicine eucommia leaf residue and Shixiajiang coal. Experiments were performed in a thermogravimetric analyzer under three different heating rates, namely 10, 20, and 30 K/min. The experimental results showed that the combustion of the blends composed of eucommia leaf residue and Shixiajiang coal could be divided into three stages. With increase of eucommia leaf residue in the blends, the ignition performance is improved first and then tends to be stable, while the combustion parameters first stay the same and then increase. The combustion kinetics of the blends were determined using the Coats-Redfern, Friedman, Kissinger-Akahira-Sunose, and Flynn-Wall-Ozawa methods. Results showed that, at the stage of volatile combustion, the change trend of activation energy of the blends is serrated; while at the stage of char combustion, the activation energy of the blends is lower than that of the Shixiajiang coal and decreases with increase of eucommia leaf residue’s ratio until 80%. The synergistic effects between the eucommia leaf residue and Shixiajiang coal were analyzed and found that the Shixiajiang coal has a restricting effect on volatilization of the eucommia leaf residue, and the eucommia leaf residue has a promotion effect for combustion of the carbon residues from Shixiajiang coal.

The organic and mineral components in two coals and resulting high-temperature ashes with high silicon content were characterized by second-derivative infrared spectroscopy, Raman spectroscopy, and X-ray diffraction (XRD). The infrared spectra of raw coals show weak organic functional groups bands but strong kaolinite bands because of the relatively high silicates content. In contrast, the Raman spectra of raw coals show strong disordered carbon bands but no mineral bands since Raman spectroscopy is highly sensitive to carbonaceous phases. The overlapping bands of mineral components (e.g., calcite, feldspar, and muscovite) were successfully resolved by the method of second-derivative infrared spectroscopy. The results of infrared spectra indicate the presence of metakaolinite in coal ashes, suggesting the thermal transformation of kaolinite during ashing. Intense quartz bands were shown in both infrared and Raman spectra of coal ashes. In addition, Raman spectra of coal ashes show a very strong characteristic band of anatase (149 cm^–1), although the titanium oxides content is very low. Combined use of second-derivative infrared spectroscopy and Raman spectroscopy provides valuable insight into the analyses of mineralogical composition. The XRD results generally agree with those of FTIR and Raman spectroscopic analyses.