|
Because of high infrared attenuation, water mist (or fog) are widely used in fire prevention and heat radiation
protection etc. However, the theoretical analysis and calculation of water mist about infrared attenuation are not easy due
to parameters that complicate the transport process, such as multi-scattering in the water mist, distribution of droplets,
concentration of droplets and water optical constant in the infrared atmosphere windows, etc. There are several methods
to calculate the water mist infrared attenuation, for example, Monte-Carlo method (MCM), independent scattering
method (ISM) and solo mean diameter method (SMDM). These methods have different accuracy and complicacy.
Theoretically, MCM should be more precision and complicated than the other methods but no report on the comparisons
between these methods is found by the authors. The present article studies the spectral transmittance of water mist with
different concentration and different thickness using MCM and Mie theory, since spectral transmittance of water mist in
the infrared atmosphere windows with lognormal distribution is important data for infrared attenuation analysis. At the
same time, the transmittance of the same water mist was calculated with ISM and SMDM and the results of MCM were
compared with those of ISM and SMDM. It is clearly indicates that the ISM is accurate when the droplet concentration is
less than 320 droplets/cm3, the SMDM is accurate when the droplet concentration was less than 300 droplets/cm3, with
variance 2 and mean diameter 8μm lognormal distribution. When the mean diameter of water mist is below 8μm, ISM
and SMDM are applicable with higher mist concentration. The ISM and SMDM is valuable for engineering calculation
about water mist infrared attenuation, when the mist concentration is not high enough.
|
