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Glumac, Nick

Publications and source records attributed to Glumac, Nick.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Sublimation and oxidation measurements of graphite and carbon black at high temperatures in a shock tube using absorption imaging and thermal emission

Surface mass loss rates due to sublimation and oxidation at temperatures of 3000–7000 K have been measured in a shock tube for graphite and carbon black (CB) particles. Diagnostics are presented for measuring surface mass loss rates by diffuse backlit illumination extinction imaging and thermal emission. Here, the surface mass loss rate is found by regression fitting extinction and emission signals with an independent spherical primary particle assumption. Measured graphite sublimation and oxidation rates are reported to be an order of magnitude greater than CB sublimation and oxidation rates. It is speculated that the difference between CB and graphite surface mass loss rates is largely due to the primary particle assumption of the presented technique which misrepresents the effective surface area of an aggregate particle where primary particles overlap and shield inner particles. Measured sublimation rates are compared to sublimation models in the literature, and it is seen graphite shows fair agreement with the models while CB underestimates, likely a result of the particle shielding affect not being considered in the sublimation model.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Near-MHz temperature and H 2 O measurements in post-detonation fireballs of 25 g hemispherical explosives using scanned-wavelength-modulation spectroscopy

A laser absorption spectroscopy diagnostic integrated within a hardened optical probe was used to measure temperature and water mole fraction at 500 kHz in post-detonation fireballs of explosives. In the experiments, an exploding-bridgewire detonator initiated a 25 g hemisphere of explosive (N5 or PETN). This produced a hemispherical fireball that traveled radially towards a hardened measurement probe. The probe contained a pressure transducer and optical equipment to pitch fiber-coupled laser light across a 12.6 cm gap onto a detector. Tunable diode lasers emitting near 7185.6 and 6806 c m − <#comment/> 1 were used to measure the absorbance spectrum of H 2 O utilizing peak-picking scanned-wavelength-modulation spectroscopy with a scan frequency of 500 kHz and modulation frequencies of 35 and 45.5 MHz, respectively. This enabled measurements of temperature and X H 2 O in the shock-heated air and trailing fireball at 500 kHz. Time histories of pressure, temperature, and H 2 O mole fraction were acquired at different standoff distances to quantify how the fireball evolved in space and time as well as to compare measured quantities between PETN and N5 fireballs. The standard deviation of temperature and X H 2 O during one representative test were found to be 17 K (1.3%) and 0.011 (5%), respectively. These measurements demonstrate this diagnostic’s ability to provide rapid and reliable measurements in harsh, highly transient post-detonation environments produced by solid explosives.

Schwartz, Charles J.↗