Abstract
In this study, the thermal shielding ability of sprays and the accompanying scientific problem of the optimal extinction diameter of moving droplets have been analyzed with the Lagrangian model and Mie theory under the overall consideration of dynamical and optical characteristics. A correction factor is introduced to eliminate the forward scattering effects of large droplets. Then, a new variable, named the thermal shielding index, has been presented as a criterion evaluating the extinction abilities of moving droplets, which analyzed the extinction performance during the whole lifetime of droplets. According to the evaluation method defined in this paper, the optimal extinction diameters obtained based on the thermal shielding index are far greater than those obtained based on the optical properties. In addition, if the initial droplet sizes were relatively large, the upward injection way will perform better than the downward injection way for a longer traveling distance and, of course, a longer lifetime.
Highlights
Water spray curtains created by injecting droplets in the air with nozzles may be used to prevent the spread of radiation from heat sources such as the flame of a fire, large scale extended hot objects, heat release of an engine, and so on
The topic of this paper focuses on the optimal extinction diameter (OED) of droplets considering both the dynamical and optical characteristics
The forward scattering effects of large droplets are eliminated by introducing a correction factor R
Summary
Water spray curtains created by injecting droplets in the air with nozzles may be used to prevent the spread of radiation from heat sources such as the flame of a fire, large scale extended hot objects, heat release of an engine, and so on. It is a critical and important application in such fields because of its high efficiency, pollution-free nature, low cost, and easy acquisition. Water spray curtains created by injecting droplets in the air with nozzles may be used to prevent the spread of radiation from heat sources such as the flame of a fire, large scale extended hot objects, heat release of an engine, and so on.1,2 It is a critical and important application in such fields because of its high efficiency, pollution-free nature, low cost, and easy acquisition. We need to first determine the size of the heat source, the radiation intensity, and the allowable spray water flow range and consider the extinction and forward scattering effects of droplets (the related parameters include the absorption and scattering coefficients, asymmetric factor, scattering phase function, etc.), absorption attenuation effects of the absorbing gas (the related parameters include concentration and absorption coefficients of H2O and CO2), the motion and evaporation effects of droplets (including the number density, droplet size spectrum, lifetime, etc.), and the radiation effects of the droplets themselves (based on Planck’s law). To the knowledge of the authors, other scholars have paid little attention to this issue, but it is very important
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