Numerical Investigation of a thermally perfect gas model for a Centrifugal Compressor Design with water vapor as working medium

Kurzfassung

Due to the use of fossil energy sources in the industry sector for which process heat is needed, the footprint on the global climate has increased significantly. The Implementation of High-Temperature Heat-Pumps (HTHP) into industry processes can make a significant contribution to reducing the consumption of fossil energy and thus to reduce the CO2 emissions. In order to realize a high Coefficient of Performance (COP) using natural refrigerants/working medium the application of Rankine thermodynamic cycle is favored. The operation of turbomachinery with a reasonable efficiency within HTHP provides high COPs and the design of the centrifugal compressor geometry considering superheated water vapor as working medium is required. Since a calorically perfect gas model is predominantly used in Computational Fluid Dynamics (CFD) for example for air as working medium with a heat capacity independent from pressure and temperature. Deviations in the evaluated performance can occur when this model is used for designing the centrifugal compressor geometry with superheated water vapor, where the heat capacity coefficients (Cv and Cp) are highly dependent on the temperature. For the numerical investigation of superheated water vapor within the CFD the influence of a thermally perfect gas model is compared to a calorically perfect ideal gas model. The influence on the operating range with respect to the design point is studied and the compressor map trend is investigated. The results of the thermally perfect gas model in the design process on the performance parameters like pressure ratio and efficiency are discussed.