Temperature and velocity fields inside a hanging droplet of a salt solution at its streamlining by a high-temperature air flow

摘要

Salt solutions are widely used in many industrial technologies, including those associated with high heat fluxes. The main constraint to the introduction of many promising high-temperature gas-vapor technologies with using salt solutions is that the mechanisms of interrelated processes of heat and mass transfer and phase transformations of such solutions under intense heating have not been sufficiently studied yet. In most modern devices, blocks and setups, intensive convective heating is realized both through gas and liquid media. As a result, the study of these processes under high-temperature convective heating is topical. The most significant results may be obtained by using the low-inertia non-contact measurement methods. This article presents the results of experimental studies of the processes of heating of drops of typical salt solutions (LiBr, CaCl2, LiCI, NaCl) placed in the flow of heated air on the holder. The temperature range was chosen from 20 degrees C to 600 degrees C to cover a large group of gas-vapor technologies, primarily evaporation (boilout) and burning (burnout) of impurities from water. Thus, the main attention was paid to the study of convective heat exchange of drops of salt solutions with a heated gas medium. The optical method Planar Laser Induced Fluorescence (PLIF) was used to control the temperature field of the droplet. The convection velocity in the droplet was registered using the optical method of Micro Particle Image Velocimetry (Micro PIV). The main attention was paid to the effects of crystallization, processes of heating and evaporation of droplets, taking into account different properties and component composition of salt solutions. The influence of these factors and processes is shown at different heat-up temperatures. The differences in the rates of heating and evaporation of salt solution drops under intense convection heating have been established. Recommendations on the application of research results for the development of promising gas-vapor technologies have been formulated. (C) 2018 Elsevier Ltd. All rights reserved.