Modeling condensation of Methane-Water vapor mixtures in the Hedba<spacing diaeresis>ck nozzle: A comparative study of 2D and 3D geometries

This study investigated the condensation behavior of a binary mixture of methane (CH4) and water vapor (H2O) within the Hedback nozzle, employing both 2D and 3D modeling approaches. The 2D model was initially developed to analyze the effects of inlet parameters and mixture's condensation characteristics. However, the inherent limitations of the 2D model in capturing the full complexity of the flow dynamics prompted a transition to a 3D modeling approach. The research explored two distinct 3D geometries: one created by extruding the 2D section and another by rotating the 2D cross-section around its axis. The latter, which more accurately represented real-world nozzle conditions, revealed differences in flow patterns, condensation behavior, and entropy generation, emphasizing the crucial role of 3D effects in the condensation process. The sensitivity of the numerical simulation results to various nucleation theories and droplet growth models was acknowledged, and the most appropriate theory and model were meticulously selected. This approach minimized discrepancies between numerical modeling outcomes and experimental data, enhancing the accuracy and reliability of the findings. The 2D results indicate a 40.5% increase in the inlet partial pressure with a constant temperature and mass fraction, resulting in a 56% rise in maximum liquid mass fraction. Similarly, a 3.6% decrease in inlet temperature under constant pressure and mass fraction increases the average radius of outlet droplets by more than 13%. In addition, entropy generation analysis revealed that less than 1% of entropy generation is attributed to mean flow, whereas 99% is linked to turbulent fluctuations. Moreover, the 3D models demonstrated markedly different entropy generation rates compared to the 2D model, highlighting the importance of 3D approach for a comprehensive understanding of thermodynamic irreversibility within the system.