CFD Analysis of Aspirator Region in a B&W Enhanced Once-Through Steam Generator

This analysis calculates the velocity profile and recirculation ratio in the aspirator region of an enhanced once-through steam generator of the Babcock & Wilcox design. This information is important to the development of accurate RELAP5 models, steam generator level calculations, steam generator downcomer models, and flow induced vibration analyses. The OpenFOAM CFD software package was used to develop the three-dimensional model of the EOTSG aspirator region, perform the calculations, and post-process the results. Through a series of cases, each improving upon the modeling accuracy of the previous, insight is gained into the importance of various modeling considerations, as well as the thermal-hydraulic behavior in the steam generator downcomer. Modeling the tube support plates and tube nest is important for the accurate prediction of flow rates above and below the aspirator port, but has little affect on the aspirator region itself. Modeling the MFW nozzle has minimal influence on the incoming steam velocity, but does create a slight azimuthal asymmetry and alter the flow pattern in the downcomer, creating recirculation patterns important to inter-phase heat transfer. Through the development of a two-phase solution that couples the aspirated steam and liquid feedwater, it was found that the ratio of droplet surface area to volume plays the most important role in determining the rate of aspiration. Calculations of the velocity profile and recirculation ratio are compared against those of historical calculations, demonstrating the possibility that these parameters were previously underpredicted. Such a conclusion can only be confidently made once experimental data is made available to validate the results of this analysis.