Abstract <p>The study is concerned with numerical simulation of carbon dioxide (СО₂) bulk condensation from its mixture with air in the flow path of a two-phase turbine machine (a turboexpander unit (TEU)) in 3D statement with using a CFD software package and the Bulk Condensation dedicated computation module. The purpose of the study is to determine the effectiveness of frequency control and its influence of the phase transition process in the turbine machine stage. The main objective of the work is to reveal the optimal operation conditions under which moisture droplets emerge and grow predominantly in the impeller channels, which corresponds to the conditions of unlikely erosion destruction of its flow path components. It is shown by calculation that by varying the TEU impeller rotation frequency it is possible to control the bulk condensation process in the radial turbine flow path. The maximal impurity condensation degree—subject to the selected constraints—that can be reached in the flow path makes more than 96% with the maximal expansion ratio equal to 6.17 and the СО₂ content in the mixture flow equal to 10 wt %. It is shown that by comprehensively varying the control parameters (expansion ratio, flow temperature, and impeller rotation frequency) it is possible to adjust the bulk condensation process intensity and also “shift” the phase transition location from the guide vane to the impeller without loss of high condensation degree and particles having sizes minimally acceptable for subsequent separation. It has been found that with increasing the impeller rotation frequency, the condensation intensity in the guide vane decreases quite rapidly, as a consequence of which this process takes place in the impeller, a circumstance that makes it possible to avoid destruction of its components under the effect of droplet impingement erosion. The simulation results are in qualitative agreement with the experimental and calculated data reported in literature sources. As regards quantitative correspondence, its assessment is rather difficult because there is lack of detailed flow path drawings, in view of which it is not possible to carry out numerical simulation.</p>