Conjugate Heat Transfer Analysis of HPGP Thruster

Sammanfattning: This master's thesis was conducted in collaboration with ECAPS, where a conjugate heat transfer analysis on their High Performance Green Propulsion (HPGP) 22N thruster was done. ECAPS is a Swedish propulsion company specializing in green propulsion. They develop thrusters for spacecraft orbit and attitude control, utilizing the propellant LMP-103S. LMP-103S is a non-toxic propellant, in contrast to the hazardous monopropellant hydrazine commonly used in thrusters. A previous master's thesis modified the original design of the 22N thruster to make it compatible with additive manufacturing. Some concerns about heat transfer in the feed tube surfaced with the new design as it showed elevated temperatures. The feed tube is a component that works as a pathway where liquid propellant is transported from the flow control assembly to the reactor chamber assembly, where combustion begins. The goal of this master's thesis was to determine the temperatures the liquid propellant reached, and to assess if the liquid propellant was at risk of vaporization in the feed tube before reaching the reactor chamber assembly. Since the feed tube is a limited volume, vaporization of the liquid propellant in the feed tube could have devastating consequences of the structure. Ansys Fluent was used as the Computational Fluid Dynamics (CFD) software, along with the Computer Aided Design (CAD) software NX and Matlab for data handling.  Four extreme case scenarios were determined to be simulated, varying the liquid propellant inlet temperatures from highest to lowest operable temperatures, as well as the thruster's highest and lowest operable inlet pressures. A literature study on conjugate heat transfer in CFD was done, along with determination and calculations of necessary parameters for a correct simulation setup, and a grid independence study. Both steady-state and transient simulations were conducted. The results indicate that when the thruster operates with the highest inlet pressure, there is a risk of vaporization, but critical consequences are less likely to have time to develop. However, for the cases where the thruster operates with its lowest inlet pressure, a significant risk of vaporization in the feed tube is present. The simulated temperature results suggest that the liquid propellant will rapidly vaporize, where increased pressure at the feed tube outlet will be building up as a result of the expanding vapor, leading to a feed tube failure for the vapor to escape through. Therefore, the new design change of the feed tube will most likely not work for the thruster to be able to work under all necessary conditions. New modifications to the feed tube are necessary, or alternatively, the original design of the feed tube could be added afterward to the 3D-printed structure, though this may result in the loss of some benefits of manufacturing the entire structure in one piece.