Effect of Structural Materials on Monopropellant Thruster Propulsion Performance in Micro Scale

Abstract

This paper reports on the effect of structural materials on heat loss-associated propulsion performance degradation of monopropellant thrusters in the micro scale. In order to address the effect of fabrication materials on heat loss, propellant flow characteristics, and propulsion performance, a conjugate heat transfer numerical study has been conducted considering several practical substrate candidates for microthrusters. The results were analyzed with respect to the thermal diffusivity of the materials, which revealed different propulsion performance characteristics and inner nozzle flow characteristics due to varying amounts of heat loss, depending on the microfabrication materials used and propellant enthalpies. Regardless of propellant enthalpies, however, there was a dramatic degradation in the amount of the thrust produced with respect to thermal diffusivity, particularly in the range of low thermal diffusivity. Glass, among the material types compatible with fabrication processes in regard to microthrusters, exhibited a 4% degradation in thrust performance for the 50 mN class microthruster considered, with the least degradation, while copper, with 7% degradation, exhibited the greatest amount of degradation among the materials considered. With varying chamber pressure and Mach number at the nozzle exit depending on structural materials, the results also indicated the necessity of heat loss consideration in a microthruster design process.