Research of temperature fields and convection velocities in evaporating water droplets using Planar Laser-Induced Fluorescence and Particle Image Velocimetry

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32 Citations (Scopus)

Abstract

Today, requirements to the resource efficiency of power plants are becoming increasingly stringent, but hardware limitations are still there. The scientific community keeps searching for the ways to intensify heat and mass transfer and phase transitions in many applications of heat and power industry, such as heaters, economizers, cooling towers, heat carriers based on flue gases, water vapors and droplets, superheaters, etc. The answer might be in the potential (or latent) reserves in the energy performance indicators of heat and mass transfer processes. One of the relevant and understudied fields is high-temperature evaporation of droplets of water and water-based emulsions, slurries, and solutions in a gas environment. Using optical methods and cross-correlation software and hardware systems, unparalleled experimental data have been obtained lately on temperature fields as well as heating and evaporation rates of liquid droplets. These experimental data provided the basis for the first models of high-temperature vaporization. However, convective flows in rapidly heated and evaporating water droplets remain unstudied. In this research, we study experimentally the macroscopic laws of convective flows forming in evaporating water droplets exposed to high-temperature (up to 500 °C) heating in a gas environment. We use Planar Laser-Induced Fluorescence and Particle Image Velocimetry for high-speed recording of temperature and velocity of liquids (droplets, films, and aerosols). Series of experiments show how long it normally takes a practically homogeneous temperature field to form in an evaporating water droplet. We also determine how water droplet heating and evaporation rates differ if there are convective flows in a droplet. Average and maximum velocities of these flows are calculated and features of vortex structures are identified, such as their location, dimensions, number, etc. Dependences are obtained of maximum convection velocities in droplets on the temperature and velocity of the incoming heated air flow as well as on the droplet size. The resulting experimental database will help develop advanced models of high-temperature droplet heating and evaporation. The results of the experimental research are processed to determine the dominating processes of heat and mass transfer in the droplets and in their near-surface steam-gas layer.

Original languageEnglish
Pages (from-to)392-407
Number of pages16
JournalExperimental Thermal and Fluid Science
Volume97
DOIs
Publication statusPublished - 1 Oct 2018

Keywords

  • Convection in droplet
  • Convection velocity and temperature field
  • High-temperature evaporation
  • Particle Image Velocimetry
  • Planar Laser-Induced Fluorescence
  • Water droplet

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Nuclear Energy and Engineering
  • Aerospace Engineering
  • Mechanical Engineering
  • Fluid Flow and Transfer Processes

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