Preparation of CO₂/N₂ cryogenic slurry and its pipeline flow characteristics

Abstract

It was proposed to use CO2/N2 to effectively prevent and control Class A solid spontaneous fires such as coal. The preparation process of CO2/N2 cryogenic slurry pipeline and its pipeline flow characteristics were studied. The temperature field, pressure field and phase change characteristic changed during the transportation of the CO2/N2 mixture in the pipeline are analyzed by numerical simulation. The results showed that: the fluid in the pipeline exchanged heat and started to contact at a position of 0.1m in the pipeline. The temperature first rapidly dropped to the lowest temperature of 103K, and then the fluids in the range of 0.1m to 0.3m were fully mixed, and the temperature rised to 164K. The temperature was consistent with the equilibrium state in the pipe, and the temperature was gentle and stable; the pressure in the pipe was on the whole downward trend, and each position along the main pipe produced a positive pressure difference relative to the end of the pipe. The closer to the mixing place, the greater the corresponding pressure difference; During the mixing process, LN2 was acted as a cold source to sublime CO2 to form dry ice particles. And through the cryogenic fluid mixing experiment, the temperature distribution in the pipeline, range of the dry ice particle generation position, and the dry ice particle generation phenomenon was measured. The results showed that the mixing was completed within 0.8 m of the pipeline, and the temperature in the tube rised to 168K and remain stable. The data were basically consistent. And dry ice particles generated at the temperature of 194.5K, and a diffuse gas cloud formed at the outlet with the momentum of the jet.