Oil-injected rotary type positive displacement compressors (RPDC) like twin-screw machines are mainly used for the compression of refrigerants in HVAC (Heating, Ventilation and Air Conditioning) systems. The efficiency of such machines is largely determined by the inevitable two-phase surge and gap flows in these types of compressors. Therefore, it is all the more remarkable that the calculation of these flows is still a challenge today. This is due to both the complexity of simulating the two-phase flow in the narrow gaps with moving boundaries as well as the lack of accurate models for the thermophysical properties of the highly asymmetric fluid mixtures of oil and refrigerant. Against this background, the proposed Research Unit provides a unique opportunity for coordinated, interdisciplinary efforts to address this knowledge gap, with seven project partners complementing each other’s capabilities. The three subprojects of group A deal with the development of new analysis and calculation methods for the two-phase gap flows while the four subprojects of group B cover the determination and modelling of the thermophysical properties of the oil-refrigerant mixtures. Within this consortium, subproject A2 aims at providing experimentally obtained information on the considered two-phase gap flows with moving boundaries as are typical for such RPDCs. For this purpose, various promising measurement strategies are combined and enhanced so as to develop a novel laser-optical high-speed imaging framework for the given target application. That is, the novel diagnostics approach is particularly optimized for the spatio-temporal evaluation of two-phase flows in thin annular rotor-stator gaps.