Modeling ex-situ thermal impulse sensor responses to non-isothermal heating profiles

Abstract

Ex-situ thermal impulse sensing based on irreversible phase transitions has been a developing field over the past two decades. Typically, these techniques determine thermal impulses assuming a perfect isothermal heating profile, which is not the case for real-life temperature profiles in extreme environments (e.g., structural fires, explosions, gas turbines). To better understand how real-world temperature profiles influence the sensors thermal impulse determinations, we perform phenomenological modeling of a thermal impulse sensor’s response to non-isothermal heating with four-key profile characteristics: finite heating rate, nonzero cooling time constant, temperature spikes, and non-isothermal heating due to the finite size of sensors. We find that in all cases, these effects result in the corresponding equivalent isothermal temperature being lower than the peak temperature, while the equivalent isothermal duration is found to either be lengthened or shortened depending on the effect of interest. These results have important implications for the interpretation of thermal impulse calculations from a wide range of ex-situ thermal impulse sensors.