Stator Blade Design of an Axial Turbine using Non-ideal Gases with Low Real-flow Effects

• Published in: Energy procedia Vol. 105; pp. 1606 - 1613
• Main Authors: Eleftheriou, K.D., Efstathiadis, T.G., Kalfas, A.I.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2017
• Subjects: ORC blade design; ORC stator blade; Supersonic flow; Supersonic flow; ORC blade design; ORC stator blade
• ISSN: 1876-6102; 1876-6102
• DOI: 10.1016/j.egypro.2017.03.515

The rising requirements for efficient energy recovery systems have led to an increasingly greater research of ORC systems. The reduction of CO2 emissions, the restricted use of fossil fuels and the enhancement of sustainable energy sources are the most important advantages of this technology. These systems function with the use of organic gases, like it can be understood from their name. The main characteristic of these gases is their large density, which means that their thermodynamic parameters vary in a different way compared to an ideal gas. Taking into account that the turbine constitutes the most important part of an ORC system, and in combination with the requirement of supersonic flow within the turbine, it is obvious that its design is a complex subject. This paper aims to investigate both the existence of a correlation between the working fluid and the geometry of the stator in an ORC system that functions with low real-flow effects gases, and the creation of a computational tool, which depending on the working fluid, will produce the preliminary geometry of a two-dimensional blade. In order to design the stator, an innovative method was used based on supersonic nozzles. For the design of the supersonic nozzles, the method of characteristics was chosen. The geometry that occurred, was checked with the use of an algorithm that solves the Euler equation system numerically. The most important advantages of the procedure described above are its simplicity as well as the precision of the provided results. Ultimately, the aforementioned procedure is applied to three types of working fluids: carbon dioxide, isobutane and R134a. Assuming a constant value of specific heat ratio, which is a realistic assumption for the operating conditions of these systems, three different blade geometries are produced. The comparison of these results shows that each working fluid, under the same operating conditions and for the same design options, has significantly differentiated two-dimensional blade geometry.