Abstract <p>The problem of deep purification of industrial gases of various impurities is urgent. The purification is usually performed using adsorption and absorption technologies, which are implemented using two-phase turbomachines with bulk condensation of the impurity in the flow path. The study is devoted to numerical simulation of the process of bulk condensation in the flow path of a radial-type refrigeration turbomachine, which is controlled by changing the flow-expansion ratio in the turbine. It is a direct continuation of the work wherein control of the process by changing the initial flow temperature was investigated. The working fluid was a mixture of air as an incondensable gas carrier and carbon dioxide as an impurity. It has been demonstrated that the process of bulk condensation proper and its depth can be controlled by changing the flow-expansion ratio. The conditions have been determined at which the process is localized predominantly in the impeller channels thereby reducing the risk of erosive wear and subsequent damage to the stage elements. For the first time, the reduction in the isentropic efficiency caused by condensation controlled by changing the flow-expansion ratio was numerically estimated for refrigeration turbomachines. The obtained data are close to the values for wet steam turbines presented in the literature. A procedure for calculating the characteristic and analyzing the results has been developed. It yields the optimal regimes using a multicriteria search with the requirements for the region where the phase transition should occur, and for the mean radius of the particles. It is shown that changing the expansion ratio may be insufficient to meet the specified requirements for the degree of condensation and isentropic efficiency offering deep purification of gases of impurities. Therefore, assessment is required as to whether the process rate can be controlled by changing the expansion ratio, the initial flow temperature, and the impeller speed.</p>