Several advantages were detected in single screw expanders as fluid expansion mechanism in Organic Rankine Cycles. In a previous development project, knowledge gaps were uncovered in the modelling of this type of expanders. The development of a complete and detailed model is an important step in the study and optimisation of the design. The developed model will be validated in an existing ORC test set-up that will be modified for this purpose during the project. Also the effect of liquid-flooded expansion and performance under part-load conditions will be examined.