Abstract
Screw-type expanders offer excellent prospects for energy conversion in lower and medium power ranges, for instance as expansion engines in Rankine cycles with regard to either waste or geothermal heat recovery. With the aim of identifying the potential in organic Rankine cycle (ORC) power systems, an oil-flooded twin-screw expander without timing gears was designed and experimentally investigated in an ORC with R245fa as working fluid. Here, the scope for the experimental determination of the expander characteristic map was limited by the test rig specifications. Based on the experimental results, a multi-chamber model of the test twin-screw expander was calibrated and theoretical approaches according to mechanical and hydraulic loss calculation were applied. Consequently, the expander’s complete characteristic map could be calculated. Furthermore, relevant mechanisms influencing the operational behaviour of oil-flooded twin-screw expanders were identified and analysed in-depth.
Highlights
Due to the growing shortage of non-renewable fossil fuel reserves and the resulting increase in primary energy costs, underdeveloped energy potentials are increasingly moving into the focus of economic interest
The purpose of the tests was to prove the suitability of a screw expander without timing gears in practice in an organic Rankine cycle (ORC) power system with a lubricating auxiliary fluid
Based on the available test results according to R245fa as working fluid, the chamber model of SE 34.5 is calibrated in terms of flow coefficients
Summary
Due to the growing shortage of non-renewable fossil fuel reserves and the resulting increase in primary energy costs, underdeveloped energy potentials are increasingly moving into the focus of economic interest. Available heat sources in the field of decentralised energy systems with small and medium power ranges from 3 kW to 1.5 MW [1,2]—such as industrial exhaust gases or waste-heat in vehicle engines, geothermal or solar thermal energy—can be converted into usable mechanical power by means of expanders or turbines within a Rankine cycle. In this context, volumetric expanders, such as sliding vane, scroll, piston, swashplate, single- or twin-screw expanders, in Rankine cycles possess clear advantages compared to turbo machines. Liquid in volumetric expanders could be beneficial with regard to their operation
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