Abstract
This paper reports a numerical study on thermal radiation transport in a novel material called dry water. Dry water is a water-in-air inverse foam which consists of micrometer-sized water droplets encapsulated by hydrophobic fumed-silica nanoparticles. First, the size distribution of dry water was measured using a particle size analyzer. Then, the radiation characteristics of dry water were obtained using the Mie theory for coated spheres. One-dimensional, steady radiative transport in fluidized dry water system was modeled using the radiative transport equation (RTE) and was solved spectrally with the discrete ordinates method. The effects of silica coating and water droplet size as well as the volume fraction of dry water particles on reducing radiative heat transfer were studied parametrically. The results obtained using the size distributions from experimental measurements at a volume fraction of 10(-4) showed that dry water reduced the local radiative heat flux by more than 60% with respect to that by silica particles alone whereas its performance was comparable to that of fine water mists. Moreover, reduction of the diameter of dry water particles from 150 to 50 mu m and increasing their volume fraction from 10(-4) to 10(-3) decreased the radiative heat flux by 45% and 67%, respectively. Dry water is a novel and unique material that does not require high pressure fluid lines for producing fine mists and features a silica shell that can serve to encapsulate water soluble compounds, retard water evaporation from the core as well as increase scattering. With these unique features, dry water finds diverse engineering applications serving as a base for photo-catalytic nanoreactors, gas and chemical storage and delivery systems, as well as alternative mist systems in firefighting. (C) 2013 Elsevier Ltd. All rights reserved.