The Importance of Temperature for Vented Chamber Calorimetry

Many accurate, calorimetric-based methodologies exist to measure the energy released from reactive materials. However, there is a need to extract energy data from non-ideal, application specific environments. High-velocity impact testing of reactive materials is one such case. A common methodology used to derive energy release in high-velocity impact testing is Vented Chamber Calorimetry (VCC). VCC relies on the measurement of both quasi-static pressure and temperature change in a vented chamber to implicitly determine energy release during impact, fragmentation, and combustion of reactive material projectiles. Due to the extreme conditions present in these experiments, VCC is often done without temperature measurements. Temperature can be mathematically estimated based on assumptions of ideal gas, however, it will be shown that this greatly reduces the accuracy of the measurement. A series of experiments were performed on a High-Velocity Impact-Ignition Testing System (HITS) with consolidated aluminum (Al) and molybdenum trioxide (MoO3) projectiles. The projectiles were launched at 1300 m/s into a vented chamber with varying volumes. Quasi-static pressure measurements were collected alongside pyrometry and thermography to determine the importance of temperature as a data point in energy derivations. Results show temperature is vital to the accurate derivation of energy. Measurements taken without temperature data assume an almost negligible temperature change in the chamber. Data from pyrometry and thermography suggest far greater average temperatures than theoretically predicted. This incongruity manifests in a greater than 100% difference for calculated energy release. Results indicate that in a highly dynamic system, pressure does not correlate directly with temperature to quantify energy released.