A diagnostic for quantifying heat flux from a thermite spray

Abstract

Characterizing the combustion behaviors of energetic materials requires diagnostic tools that are often not readily or commercially available. For example, a jet of thermite spray provides a high temperature and pressure reaction that can also be highly corrosive and promote undesirable conditions for the survivability of any sensor. Developing a diagnostic to quantify heat flux from a thermite spray is the objective of this study. Quick response sensors such as thin film heat flux sensors cannot survive the harsh conditions of the spray, but more rugged sensors lack the response time for the resolution desired. A sensor that will allow for adequate response time while surviving the entire test duration was constructed. The sensor outputs interior temperatures of the probes at known locations and utilizes an inverse heat conduction code to calculate heat flux values. The details of this device are discussed and illustrated. Temperature and heat flux measurements of various thermite sprays are reported. Results indicate that this newly designed heat flux sensor provides quantitative data with good repeatability suitable for characterizing energetic material combustion.

Factors Affecting Substrate Heating with Printed Thermites

“…Here, net retained masses of between 11 and 52 % have been observed with heating efficiencies of 4.4 to 42.4 % calculated when using glass substrates. Nixon et al [48] reported 10-17 % heating efficiency; however, they were heating a substrate with the directed flame from thermite rather than burning the thermite on the substrate, which isn't comparable to the present work. Crane et al [41] burned thermite powders on a steel substrate and measured heat transfer efficiencies between 4.6 and 52 %.…”

Heat Flux Analysis of a Reacting Thermite Spray Impingent on a Substrate

“…Ignition ports are positioned to allow for the nichrome wire to enter the acrylic cup and allow for clearance from the nozzle. The angle of the nozzle has been tested, and results show that the energy of the spray is maximized at 45° from the centerline (see Figure b) . The material used for the nozzle, body, and end plug is grade G10/FR4 Garolite from McMaster-Carr.…”

“…Quantifying the energy from thermite combustion impingent upon a substrate has only recently been documented by Nixon et al They engineered a heat flux sensor that could withstand the high temperature and corrosive nature of a thermite spray. Using a series of probes (each fitted with thermocouples), the temperature was measured and the heat flux was calculated for an Al + CuO reaction spray impingent on the sensor.…”

“…These results were used to optimize the design of the thermite spray nozzle. Their calculations showed that roughly 17% of the theoretical heat of combustion was delivered to the sensor …”

“…Design improvements were made to the heat flux sensor originally presented in refs and . Specifically, the heat flux sensor responds at least 10 times faster than the previous sensor with improved spatial resolution.…”