Mixing at transcritical conditions

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Mixing processes of two fluid compounds are transcritical, when the initial states of the two fluids (before mixing) do not allow a definite prediction on whether the mixing will take place in a single- or in two-phases. Though mixing at transcritical conditions is widely used in propulsion systems and diesel motors, in the novel CryoPower recuperated split cycle engine (RSCE) and high pressure processes for particle generation, we do not have a clear understanding about the relevance of the different mechanisms (two-phase vs single-phase mixing) involved into mixture formation. As a consequence, there is currently no consensus about how transcritical mixing can be modelled best in order to reliably reflect the relevant mechanisms. The data-availability on quantitative experimental insights into transcritical mixing processes is rare. Therefore, the main aim of this proposal is the experimental provision of quantitative mixture compositions and temperature couples along real transcritical mixing path trajectories (work packages 2 & 3), which in the future can serve as quantitative reference for modelling approaches. The comparison of real vs theoretical mixing path trajectories (work packages 4 & 5), will reveal to which extent (i) the departure from thermodynamic equilibrium, (ii) the degradation of a phase interface and (iii) the different rates of energy and mass transport due to the additional thermal and mass diffusion, have to be regarded in the models for the description of transcritical mixing processes. The quantitative composition/temperature-data (spatially resolved) will be provided via the combination of various complementary optical measurement techniques. To a large extend the project is based on the utilization of already existing either composition or temperature data, which through this proposal will be supplemented to high-value couples of correlated compositional and temperature data.