Droplet size and transmittance spectra of mechanically generated water fogs

Abstract

The concept of using commercially available water fog generators to simulate natural fogs and military obscurants is investigated. Results obtained with a high-pressure direct impaction system developed for agricultural and environmental control applications are reported. Experiments verify that such systems can produce optically dense “artificial fogs” similar in appearance to natural fogs under favorable meteorological conditions. Measurements of the droplet mass distribution function indicate a broad spectrum in the lower size region (0.3–1.5 μm) and a marked peak in the upper region at a diameter of about 17 μm. Experiments show that droplet size can be partially controlled with common surfactants and inhibitors. The artificially generated fogs are good broadband obscurants, exhibiting a nearly flat transmittance spectrum in the visible through mid-infrared regions with a broad peak in the far infrared region. The measured extinction spectrum is similar to natural fogs, being in between the advective and radiative cases.