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

• A series of systematic flammability tests with Laser Diffraction Particle Analysis methodology was carried out within it.
• Factors affecting ignitable region of aerosols were identified as droplet sizes and volumetric concentration of evaporated vapors.
• Observations of the aerosol combustion process and ignition delay phenomenon were provided. The three-stage combustion mechanism was indicated.
• An ignitibility characterization was conducted to identify potential parameters affecting aerosol fire hazards.

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.