Felix Reinker

Boiling Under Hele-Shaw Flow Conditions: The Occurrence of Viscous Fingering

Boiling and bubble dynamics were experimentally investigated in a Hele-Shaw flow cell using pure water at atmospheric pressure as working fluid. The resulting vapor bubble shapes were recorded by means of a high-speed camera for several plate spacings and heating power levels. It was found that viscous fingering phenomena of vapor bubbles occurred only under very special boiling conditions and cell parameters. The evaporation front velocity was identified as a major parameter for the onset of viscous fingering. The observed basic viscous fingering dynamics was in reasonable agreement with theoretical analyses. In addition to that classical viscous large fingering, small-scale evaporation instability was observed leading to microscopic roughening of accelerating evaporation fronts. This instability might be explicitly related to evaporative heat and mass transfer effects across the fast-moving phase interface.Copyright

A Modular Low-Speed Wind Tunnel With Two Test Sections and Variable Inflow Angle

A modular low-speed wind tunnel system was designed and developed. Due to the modular concept, the wind tunnel permitted open-jet operation, cascade testing or closed-circuit operation. The closed-circuit wind tunnel had two test sections, and it had a high quality test-section with variable flow angle that is particular valuable for airfoil or blade testing. Physical calibration of the wind tunnel facility validated the design rules and CFD methods used and demonstrated that these techniques can be employed successfully for future wind tunnel designs. A detailed study of the thermal behavior of the closed-circuit wind tunnel was conducted. A feedback control method based on a PI control law was developed and tested for the wind tunnel speed.Copyright

Performance Predictions of Axial Turbines for Organic Rankine Cycle (ORC) Applications Based on Measurements of the Flow Through Two-Dimensional Cascades of Blades

The Organic-Rankine-Cycle (ORC) offers a great potential for waste heat recovery and use of low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low temperature level, and it is, therefore, of major importance to design ORC components with high efficiencies and minimized losses. The use of organic fluids creates new challenges for turbine design, due to real-gas behavior and low speed of sound. The design and performance predictions for steam and gas turbines have been mainly based on measurements and numerical simulations of flow through two-dimensional cascades of blades. In case of ORC turbines and related fluids, such an approach requires the use of specially designed closed cascade wind tunnels. In this contribution, the specific loss mechanisms caused by the organic fluids are reviewed. The concept and design of an ORC cascade wind tunnel are presented. This closed wind tunnel can operate at higher pressure and temperature levels, and this allows for an investigation of typical organic fluids and their real-gas behavior. The choice of suitable test fluids is discussed based on the specific loss mechanisms in ORC turbine cascades. In future work, we are going to exploit large-eddy-simulation (LES) techniques for calculating flow separation and losses. For the validation of this approach and benchmarking different sub-grid models, experimental data of blade cascade tests are crucial. The testing facility is part of a large research project aiming at obtaining loss correlations for performance predictions of ORC turbines and processes, and it is supported by the German Ministry for Education and Research (BMBF).Copyright

Development of a Cost-Efficient Test Rig for Turbine Loss Education

A large number of approaches have been made to predict the total pressure loss coefficients and flow deviation angles to the geometry of turbine cascades and the incoming flow. Students feel typically uncomfortable when faced with turbine loss coefficients during their education, and it is challenging to fully understand turbine losses only by means of theory. The integration of a turbine cascade facility into academic courses might be useful but such test facilities are expensive or not available for a large number of engineering schools. To overcome this issue, a cost-efficient test rig for measurements of the flow through a two-dimensional cascade of turbine blades was designed. This test rig enabled the measurement of the flow through a blade cascade and the formation of wakes. The effect of the inlet flow angle on the cascade performance was investigated easily by students. Based on own measurements, the students were able to apply the most prominent approaches for determining loss coefficients. Furthermore, they compared their results with literature data and predictions of available correlations. By doing that, the importance of blade spacing and Reynolds number level on profile loss coefficients became more transparent and invited to further studies.© 2014 ASME