Browsing by Author "Dean, Steven W."
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Item Comparing pyrometry and thermography in ballistic impact experiments(2022) Woodruff, Connor (TTU); Dean, Steven W.; Cagle, Colton (TTU); Croessmann, Charles Luke (TTU); Pantoya, Michelle L. (TTU)Thermal analyses of projectile impact and subsequent combustion are investigated for aluminum projectiles using a high-velocity impact ignition system. Temperature measurements are compared using pyrometry and thermography. The implementation of these techniques is discussed, as well as their benefits and limitations in ballistic experiments. Results show pyrometry is best for measuring temperatures in the immediate vicinity surrounding the impact location, while thermography better quantifies temperature dissipation downstream from impact as the combusting debris cloud disperses. Temperatures comparable to the predicted adiabatic flame temperature are observed with the pyrometer. For thermography, emphasis is placed on the treatment of emissivity in temperature calculations. Three combustion stages are identified in the thermography data and attributed to 1) ignition and growth of the combustion front, 2) thermal dissipation due to initial particle burnout, and 3) a slower dissipation stage caused by reduced heat exchange between the burning debris cloud and surroundings.Item Comparison of pyrometry and thermography for thermal analysis of thermite reactions(2021) Woodruff, Connor (TTU); Dean, Steven W.; Pantoya, Michelle L. (TTU)This study examines the thermal behavior of a laser ignited thermite composed of aluminum and bismuth trioxide. Temperature data were collected during the reaction using a four-color pyrometer and a high-speed color camera modified for thermography. The two diagnostics were arranged to collect data simultaneously, with similar fields of view and with similar data acquisition rates, so that the two techniques could be directly compared. Results show that at initial and final stages of the reaction, a lower signal-to-noise ratio affects the accuracy of the measured temperatures. Both diagnostics captured the same trends in transient thermal behavior, but the average temperatures measured with thermography were about 750 K higher than those from the pyrometer. This difference was attributed to the lower dynamic range of the thermography camera’s image sensor, which was unable to resolve cooler temperatures in the field of view as well as the photomultiplier tube sensors in the pyrometer. Overall, while the camera could not accurately capture the average temperature of a scene, its ability to capture peak temperatures and spatial data make it the preferred method for tracking thermal behavior in thermite reactions.Item The influence of gas generation on flame propagation for nano-Al based energetic materials(2008-12) Dean, Steven W.; Pantoya, Michelle; Weeks, Brandon L.; Levitas, ValeryThis study examines the reactions of two nanocomposite thermites, aluminum (Al) with copper oxide (CuO) and aluminum with nickel oxide (NiO). These oxidizers were selected based on their predicted properties: similar adiabatic flame temperatures but significantly opposing gas generation properties. Thermal equilibrium calculations predicted that the Al+CuO would have a high gas output and the Al+NiO would produce little to no gas. Flame propagation rates and peak pressure measurements were taken for both composites at various equivalence ratios using an instrumented flame tube apparatus. Results show that over the range of equivalence ratios studied, Al+CuO had an average propagation rate of 582.9 ± 87.6 m/s, while Al+NiO had an average velocity of 193.7 ± 72.2 m/s. The average peak pressures observed for the reactions were 3.75 ± 0.85 MPa for Al+CuO and 1.68 ± 0.88 MPa for Al+NiO. A DSC/TGA was also used to determine the properties of the composites and reactants under low heating rates. These low heating rate tests indicate that the gas production properties of the composites are highly dependent on heating rate, with both composites experiencing almost no mass loss under slow heating. The results suggest that the melt-dispersion mechanism, which is only engaged at high heating rates, leads to a dispersion of high velocity molten Al clusters that promotes a pressure build-up by inducing a bulk movement of fluid. This mechanism may promote convection without the need for additional gas generation.