Numerische und experimentelle Analyse des energetischen Wirkungsgrades von Flüssigkeitkolbenstirlingmaschinen

The stirling engine has some advantages like, working from any heat source, high theoretical effiency and quiet operation. In Order to solve problems of actual Stirling engines, like poor heat transfer between the working gas and surrounding walls, difficulties in sealing low molecular weight gases at high pressure and efficiency losses due to continuous cylinder movement with overlapping cycle steps, the liquid piston concept is intended to improve the efficiency of compression and expansion steps in the Stirling process. Within this concept a liquid piston instead of a solid piston is utilized to compress or expand a gas, to realize near isothermal processes.In order to obtain design guidelines for liquid piston Stirling engines with maximum power and efficiency, a simulation model is developed in this work. The heat transfer between the working gas and the surrounding walls is an important information for the simulation model. For this reason a computational fluid dynamics (CFD) model is presented in addition, analysing the heat transfer by the influence of compression time and diameter of a cylindrical working chamber. In order to verify the CFD-model, the results are compared to measured experimental data from a testing device. The results showed a good match in local temperature and pressure between CFD-model and experimental data. Results display heat transfer coefficients of 80 - 340 W/m2/K at different working chamber diameter and cycle time. These results were applied to the simulation model for liquid piston Stirling engines.The case study analyses the operation for an engine configuration with eight working chambers. After optimizing the hydraulic components, pipes and valves the results show, an electrical power outputof 32,5 kW and an efficiency of 45,4%.