<p> Embedding thermally conductive wires in a propellant has been known as an alternative means of increasing the burning rate of the propellant. The wires conduct heat into the propellant, preheating the material surrounding the wire and locally increasing the burning rate around the wire. As the propellant burns, a cone forms around the wire, exposing more burning surface area, which in turn increases the chamber pressure and consequently the bulk burning rate of the propellant. Likewise, embedded reactive wires have been considered in solid propellants for decades. Typically, these wires have been metal-metal reactive materials (intermetalics), but more recently metal-fluoropolymer materials have been considered. These reactive wires are consumable energetic materials that burn faster than the propellant, which allows them to expose more burning surface area by igniting the propellant faster than the burning front can proceed. Some of these reactive wire materials have also been shown to be additively manufacturable, allowing them to be printed in complex geometries, which further increases the tailorability of the burning surface profile. Previous studies on inert wires have largely focused on double base formulations, but few have considered composite propellants. These studies cast the wires against a window in order to visualize the burning that may affect the results. A few studies have also been performed with embedded reactive wires at elevated pressures, again cast against a window, which may have affected the burning dynamics by acting as an additional path for heat loss. This work studied whether the window affected the deflagration dynamics of embedded wire samples by comparing the combustion of windowed samples to full strand samples with propellant surround all sides of the wire and visualized with dynamic X-rays. High purity copper and silver wire were embedded in diameters of 0.405, 0.644, and 0.812 mm (26, 22, and 20 AWG) as inert, thermally conductive wires. A 20 wt. % active nanoscale aluminum and polyvinylidene fluoride reactive wire extruded using a 1.6 mm nozzle was also embedded for comparison to the inert wires. The windowed samples were tested in open air and in a Crawford strand burner at elevated pressures, using a high speed camera to view how the deflagration progressed along the wire against the window. The full strand samples were tested in open air using X-ray radiography to view the cone forming around the embedded wire. A burning rate enhancement was able to be measured from the burning profile around the wire. No statistically significant differences between the average measurements of windowed samples and full strand samples were found except in the case of 20 AWG Ag wire. The burning rate enhancement of the reactive wire was found to increase with increasing pressure, whereas the inert wires showed a decrease in burning rate enhancement. This effect is due to the reaction rate of the reactive wire increasing with pressure, whereas heat conduction along a metal wire is not dependent on pressure. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/20399016 |
| Date | 28 July 2022 |
| Creators | Usman Ashraf Bajwa (13171308) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/EFFECTS_OF_EMBEDDED_INERT_AND_REACTIVE_WIRES_AND_THEIR_TESTING_METHODS_ON_THE_DEFLAGRATION_DYNAMICS_OF_AN_AMMONIUM_PERCHLORATE_COMPOSITE_PROPELLANT/20399016 |
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