Application of the Planar Laser-Induced Fluorescence Method to Determine the Temperature Field of Water Droplets under Intensive Heating

Presented are results of experimental investigations concerned with formation of a nonstationary and essentially nonuniform temperature field of a water droplet (initial radius of 1 mm to 2 mm) under intensive heating in a flow of heated air (from 50 degrees C to 1000 degrees C). The method used for this purpose was a noncontact optical planar laser-induced fluorescence (PLIF) method. It is shown that temperature distribution in a water droplet is essentially inhomogeneous even under prolonged heating (to several tens of seconds). Reliability of the results of measurements by the noncontact PLIF method was analyzed by applying a group of fast miniature thermocouples. Restrictions of using the PLIF method for studying temperatures fields of evaporating droplets under high-temperature heating (over 800 degrees C) were marked out. Characteristic times of droplet existence (complete evaporation) were determined. It was analyzed how the temperature difference in a water droplet affects this parameter during heating and intensive phase transitions. It was substantiated that it is expedient to consider essentially inhomogeneous and nonstationary temperature field of a water droplet inmathematical modeling of the heat andmass transfer processes in high-temperature gas-vapor-droplet systems (corresponding, e.g., to burning or heat cleaning of liquids, firefighting, production of composite and gaseous fuels, their combustion, etc.).