RADIATIVE PROPERTIES OF NANO-ENERGETIC MATERIALS

2007 ◽  
Vol 6 (1) ◽  
pp. 105-118
Author(s):  
M. Quinn Brewster ◽  
S. M. Begley
Keyword(s):  
Energetic Materials ◽  
Radiative Properties

Radiative Properties of MoO3 and Al Nanopowders From Light-Scattering Measurements

2006 ◽  
Vol 129 (5) ◽  
pp. 624-633 ◽  
Author(s):  
S. M. Begley ◽  
M. Q. Brewster
Keyword(s):  
Light Scattering ◽  
Energetic Materials ◽  
Energy Transport ◽  
Molybdenum Trioxide ◽  
Radiative Properties ◽  
Isotropic Scattering ◽  
Relative Contribution ◽  
Micron Size ◽  
Scattering Measurements ◽  
Burning Rates

The combustion behavior of nanometer-scale energetic materials is much different than micron size or larger materials. Burning rates up to 950 m∕s have been reported for a thermite composition of nanosized aluminum and molybdenum trioxide. The energy transport mechanisms in the reactive wave are still uncertain. The relative contribution of radiation has not yet been quantified. To do so analytically requires dependent scattering theory, which has not yet been fully developed. Radiative properties for nanoaluminum and nanomolybdenum-trioxide were obtained experimentally by comparing light scattering measurements on a one-dimensional slab of powder with multiple-scattering simulations using Monte Carlo and discrete ordinate methods. The equivalent isotropic-scattering extinction coefficient for close-packed molybdenum trioxide (MoO3) nanopowder was found to be 5900±450cm−1; the equivalent isotropic-scattering albedo was 0.97±0.035. Aluminum (Al), which proved to be more difficult to work with, had an albedo of 0.35 and 0.38 from two tests. The radiative conductivity based on the MoO3 results is two orders of magnitude less than the diffusive thermal conductivity, indicating that radiation is not a dominant heat transfer mode for the reactive wave propagation of nanothermites under optically thick conditions.

Characterizing the convective heat exchange with plastic shading nets under natural arid conditions

2019 ◽  
pp. 11-20
Author(s):  
Ahmed M Abdel-Ghanya ◽  
Ibrahim M Al-Helal
Keyword(s):  
Wind Speed ◽  
Thermal Radiation ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Convective Heat Exchange ◽  
Radiative Properties ◽  
Wooden Frame ◽  
Arid Conditions ◽  
Air Temperatures ◽  
Radiation Fluxes

Plastic nets are extensively used for shading purposes in arid regions such as in the Arabian Peninsula. Quantifying the convection exchange with shading net and understanding the mechanisms (free, mixed and forced) of convection are essential for analyzing energy exchange with shading nets. Unlike solar and thermal radiation, the convective energy, convective heat transfer coefficient and the nature of convection have never been theoretically estimated or experimentally measured for plastic nets under arid conditions. In this study, the convected heat exchanges with different plastic nets were quantified based on an energy balance applied to the nets under outdoor natural conditions. Therefore, each net was tacked onto a wooden frame, fixed horizontally at 1.5-m height over the floor. The downward and upward solar and thermal radiation fluxes were measured below and above each net on sunny days; also the wind speed over the net, and the net and air temperatures were measured, simultaneously. Nets with different porosities, colors and texture structures were used for the study. The short and long wave’s radiative properties of the nets were pre-determined in previous studies to be used. Re and Gr numbers were determined and used to characterize the convection mechanism over each net. The results showed that forced and mixed convection are the dominant modes existing over the nets during most of the day and night times. The nature of convection over nets depends mainly on the wind speed, net-air temperature difference and texture shape of the net rather than its color and its porosity.

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