Experimental Investigation of Condensing Two-Phase Flows in a Turbocharger Turbine for Fuel Cell Applications

Abstract The development of turbocharger turbines for fuel cell (FC) applications introduces unique challenges due to the working fluid. High humidity air as exhaust gas from the fuel cell can lead to condensation effects that are absent in conventional turbocharger turbines. This can have an influence on the efficiency as well as on the durability of components due to coarse water droplet erosion. There exist several experimental as well as numerical investigations on the condensation effects of humid air, but there is no evident data of droplet measurements in a FC turbocharger turbine application in the open literature. To address this, experimental investigations are presented to examine condensing two-phase flows in an FC turbocharger turbine. A dedicated test section is developed to acquire detailed data of the expansion of the flow, the flow field as well as the droplet distribution at a defined cross section downstream of the turbine. Generic inlet conditions reproduce the FC exhaust gas with varying pressure, temperature and relative humidity. A light extinction method is applied for precise droplet measurements. The flow field is measured using a 5-hole probe featuring thermocouples. A detailed design of experiments (DOE) is set-up to assess the influence of the inlet conditions on droplet formation. The test data acquired is used to validate CFD simulations modeling the expansion of humid air employing an adapted phase transition model. The CFD simulation results correlate well to test data, especially what regards the flow field and the overall trends in liquid volume fraction and droplet diameters. The proposed paper presents the instrumentation developed for measurements of condensing flows in FC turbines and discusses the agreement of CFD simulation results to test data.