Numerical Simulation of Two-Phase Flow in the Second Header of MAC Condenser 2019-01-1065

Phase separation circuiting has been proved in the past to effectively improve the performance of MAC condensers. In the vertical second header of the condenser, liquid separates from vapor mainly due to gravity, leaving vapor-rich flow with higher heat transfer coefficient to go into the upper passes. The condenser effectiveness is improved in this way. However, separation is usually not perfect, expressed through the separation efficiency (ηl and ηv). This paper presents the numerical study of phase separation phenomena in the second header. Based on different flow regimes, Euler-Euler method and Eulerian-Lagrangian method of CFD are used. Simulations are conducted for two-phase refrigerants: R-134a and R-245fa. Inlet mass flux is controlled in the range of 87 kg∙m-2∙s-1 – 311 kg∙m-2∙s-1 and inlet quality in 0.25 – 0.5. The CFD simulation is compared to the experimental results with flow visualization and the results of a simple mechanistic model based on empirical correlations. Results agree well with each other. Conclusion can be drawn that liquid separation efficiency ηl can be 100% at low inlet mass flux. Increase of header diameter effectively improves ηl. Simulations are also done to discuss the effect of fluid properties on separation.