The characterization of heat transfer fluid P-NF aerosol combustion: Ignitable region and flame development

Heat transfer fluids tend to form aerosols due to the operating conditions at high pressure when accidental leaking occurs in pipelines or storage vessels, which may cause serious fires and explosions. Due to the physical property complexity of aerosols, it is difficult to define a standard term of “flammability limits” as is possible for gases. The study discussed in this paper primarily focuses on the characterization of ignition conditions and flame development of heat transfer fluid aerosols. The flammable region of a widely-used commercial heat transfer fluid, Paratherm NF (P-NF), was analyzed by electro-spray generation with a laser diffraction particle analysis method. The aerosol ignition behavior depends on the droplet size and concentration of the aerosol. From the adjustment of differently applied electro-spray voltages (7–10 kV) and various liquid feeding rates, a flammable condition distribution was obtained by comparison of droplet size and concentration. An appropriate amount (0.3–1.2 ppm) of smaller droplets (80–110 μm) existing in a given space could result in successful flame formation, while larger droplets (up to 190 μm) have a relatively narrowed range of flammable conditions (0.7–0.9 ppm). It is possible to generate a more useful reference for industry and lab scale consideration when handling liquids. This paper provides initial flammability criteria for analyzing P-NF aerosol fire hazards in terms of droplet size and volumetric concentration, discusses the observation of aerosol combustion processes, and summarizes an ignition delay phenomenon. All of the fundamental study results are to be applied to practical cases with fire hazards analysis, pressurized liquid handling, and mitigation system design once there is a better understanding of aerosols formed by high-flash point materials.     

低温液体在水中快速相变过程流动与传热数值模拟

用试验和理论分析的方法对快速相变爆炸强度的预测缺乏定量模型,因此建立了一种欧拉-欧拉双流体多相流模型与传热模型相互耦合的数值模型,并通过与Clarke H将液氮喷射入水的快速相变试验数据对比来验证模型的可靠性和正确性。通过数值计算得出快速相变过程中流场、压力场、温度场随时间变化的情况,探讨了快速相变的传热机理。结果表明:快速相变是强制对流、膜态沸腾、爆发沸腾和核态沸腾之间的转换过程;相间换热系数随时间的无量纲变化关系可以用3个高斯分布的叠加来描述。