Nonclassical behavior of dense gases in axial cascades

The behavior of dense gases can be described by the fundamental gasdynamic derivative Γ. In flows of highmolecular hydrocarbons and fluorocarbons nonclassical effects like an increase of the speed of sound during isentropic expansion are possible in a wide range outside of the dense gas region if Γ < 1. For a perfect gas is Γ = 1.2 if γ = 1.4 (γ is the ratio of the specific heats). Close to the thermodynamical critical point Γ even may become negative. There expansion shocks are possible and compression shocks are prohibited by the second law of thermodynamics. For technical application these fluids are important in organic Rankine cycles (ORC) which are used in power plants to recover waste heat energy. The low value of the speed of sound of these fluids down to 50 m/s requires proper design of the turbine. The 2-D Euler equations are solved numerically by a finite volume method of Jameson where the equation of state of van der Waals is applied to investigate the behavior of these fluids in axial cascades. Perfect gas and dense gas reveal completely different shock structures. This leads to a reduction of shock losses and enables to improve the efficiency of organic Rankine cycles.