In this study, a finite volume simulation framework was developed, validated, and employed for the first time in a new solid-state additive manufacturing and repair process, Additive Friction Stir Deposition (AFSD). The open-source computational fluid dynamics (CFD) code openfoam was used to simulate the deposition of a single layer of Aluminum Alloy 6061 feedstock onto a substrate, using a viscoplastic model to predict the flow behavior of the material. Conjugate heat transfer was considered between the build layer, the surrounding atmosphere, and the substrate, and the resulting temperatures were validated against experimental data recorded for three processing cases. Excellent agreement between simulated and measured temperature data was obtained, as well as a good qualitative prediction of overall build layer morphology. Further analysis of the temperature field was conducted to reveal the variation of temperature in the build direction, an analysis not possible with previous experimental or numerical methods, as well as a global heat transfer analysis to determine the relative importance of various modes of heat input and cooling. Tool heating was found to be the primary heat input to the system, representing 73% of energy input, while conduction to the substrate was the main mode of part cooling, representing 73% of heat loss from the build layer.