This thesis presents the development of a numerical model for scrollcompressors and expanders operating with supercritical carbon dioxide(sCO2) as the working fluid. The insights gained aim to support the design andoptimization of scroll machines for supercritical CO2 applications, particularlyin the context of waste heat recovery cycles, while identifying future stepsneeded to validate and enhance the model.The study addresses key challenges in scroll machine modeling, includingthe accurate representation of internal leakage with supercritical CO2. Thestudy compares various leakage modeling approaches in scroll machines withsupercritical CO2 flow modeling through orifice methods. Finally, the selectedmethods are evaluated to assess their impact on the overall performance of themodel.Additionally, the thesis investigates the thermal modeling of the scroll,including heat transfer correlations tailored for supercritical CO2, and assessestheir influence on the accuracy and reliability of the numerical model. Thefindings provide a foundation for further advancements in scroll machinedevelopment and contribute to the broader understanding of supercritical CO2behavior in such systems.