(104an) Aerosol Flammabiltiy Study of Heat Transfer Fluid: Flammable Regions, Flame Development, and Ignition Delay Modeling

Existence of flammable aerosols creates fire and explosion hazards in the process industry. Due to the operation condition of high pressure circumstances, heat transfer fluids tend to form aerosol when accident leaking occurs on pipelines or storage vessels. Aerosol system is a complicated reactive system, of which the flammability is usually decided by the balancing relations of droplet size and concentration. However, there are neither systematic flammability limits data similar to the case with pure gases, nor clearly described ignition-to-combustion process of droplet-air mixture system. A widely used commercial heat transfer fluid, P-NF, was generated by electrospray and analyzed with laser diffraction particle analysis method as our target of research.  By applying different voltages in electrospray and various liquid feeding rates we were able to get an accurate flammable condition distribution. Appropriate amount of smaller droplets existing in specific space could easily result in successful flame formation even the heating temperature was under the flash point of fuel, while larger droplets had relatively narrowed range of flammable conditions. We then could generate a useful reference for industry and lab scale consideration while handling liquids. On the other hand, the process of combustion from initial stage to global flame formation was simulated with COMSOL-multiphysics in terms of heat transfer, droplet evaporation, and fluidynamics of liquid-air interaction. The local temperature change through time, as an indicator of luminous flame appearance, was analyzed to describe the flame development and ignition delay time of aerosols. Simulation results were compared with lab data to approach the conclusion of flame formation frequency after the ignitable conditions were achieved with aerosols, and potential mitigation method and implemented timing could also be revealed.