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Influence of real gas model on the simulation of pressure pulsation in the reciprocating compressor manifolds

Cyklis P., Hendla R.

Archives of Thermodynamics

2005

Vol. 26, no. 3

21-35

Pressure pulsations in positive-displacement gas compressor manifolds have significant effect on the functioning of the entire manifold. In practical modelling of the pressure pulsations the ideal gas model is usually used. Although in many cases sufficient, this approach often does not allow to reach the required accuracy. Especially in the case of media with complicated molecular structures, high pressures and high temperatures. In this paper a comparison between different gas models for the real working medium pulsating flow is shown. The effects of the equation of state on the modelling accuracy is described in detail, and theoretically determined diagrams of the errors of the compressibility coefficient [o'] in certain areas of thermodynamic parameters are shown. Theoretical discussion is correlated with the results of CFD simulations of the oil separator (compressor manifold element) model, and with the experimental data.As the effect, differences in the results obtained for particular gas models are shown. Presented analysis shows, that the relatively most effective means of analysing pressure pulsations, using the CFD methods, is the application of the empirical equation of state for the carefully averaged value of the coefficient of compressibility.

Numerical calculation of the steam condensing flow

Dykas S.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

2001

Vol. 5, No 4

519-535

Considering the flow in the last stages of LP (low pressure) steam turbine the strong non-linearity of the thermal parameters of state and possibility of the two-phase flow have to be taken into account in the numerical calculation of the flow field. In this paper numerical calculations of the steam condensing flow for the turbine geometry are presented. The steam properties are described here on the basis of the IAPWS’97 formulation. The classical nucleation theory of Volmer and Frenkel was adapted for modelling of condensing flow. The droplet growth model of Gyarmathy is implemented. The calculations are based on the time dependent 3D Euler equations, which are coupled to three additional mass conservation equations for the liquid phase and are solved in conservative form.