Thermocouple Temperature Measurements in Metalized Explosive Fireballs

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 6806c m -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.

Near-MHz temperature and H2O measurements in post-detonation fireballs of 25  g hemispherical explosives using scanned-wavelength-modulation spectroscopy.

A numerical simulation study was performed to examine the post-detonation reaction processes produced by the detonation of a 12 mm diameter hemispherical pentaerythritol tetranitrate (PETN) explosive charge. The simulations used a finite rate detailed chemical reaction model consisting of 59 species and 368 reactions to capture post-detonation reaction processes including air dissociation from Mach 19+ shock waves that initially break out of the PETN charge, reactions within the detonation products during expansion, and afterburning when the detonation products mix with the shock heated air. The multi-species and thermodynamically complete Becker–Kistiakowsky–Wilson real-gas equation of state is used for the gaseous phase to allow for the mixing of reactive species. A recent simplified reactive burn model is used to propagate the detonation through the charge and allow for detailed post-detonation reaction processes. The computed blast, shock structures, and mole fractions of species within the detonation products agree well with experimental measurements. A comparison of the simulation results to equilibrium calculations indicates that the assumption of a local equilibrium is fairly accurate until the detonation products rapidly cool to temperatures in the range of 1500–1900 K by expansion waves. Below this range, the computed results show mole fractions that are nearly chemically frozen within the detonation products for a significant portion of expansion. These results are consistent with the freeze out approximation used in the blast modeling community.

https://pubs.aip.org/aip/pof/article-pdf/doi/10.1063/5.0153334/17978650/066117_1_5.0153334.pdf

Post-detonation fireball modeling: Validation of freeze out approximations


 Real-time access to critical information about system temperature variations is essential for evaluating system performance in some of the high-temperature and harsh environments. Given the technical difficulty of accurately obtaining the temperature of a high-temperature and harsh environment, a new sensor package structure is proposed. Combining ceramic sintering and isostatic pressure molding methods, the thermal junction is fixed in the temperature measurement end face of the alumina ceramic substrate, while the shell design threads play a role in fixing the sensor and preventing loosening. This paper conducted repeatability, upper-temperature limit, and high-temperature serviceability assessment tests on the sensor. The results show that the sensor maximum repeatability error is 2.4%. The sensor can continue to operate at 1200°C for more than 6 hours with no signal interruption and the upper limit of temperature measurement is 1307°C. The results demonstrate the feasibility and practicality of temperature measurement by this sensor in high-temperature and harsh environments.

A novel sensor with excellent high-temperature performance for in-situ temperature measurement

Measurement of temperature and water vapor concentration using laser absorption spectroscopy in kilogram-scale explosive fireballs

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Measurement of temperature and water vapor concentration using laser absorption spectroscopy in kilogram-scale explosive fireballs