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Science and Technology of Nuclear Installations
Volume 2018 (2018), Article ID 2153019, 10 pages
https://doi.org/10.1155/2018/2153019
Research Article

On the One-Dimensional Modeling of Vertical Upward Bubbly Flow

1Department of Mechanical Engineering and Construction, Universitat Jaume I, Campus del Riu Sec, 12080 Castelló de la Plana, Spain
2Institute for Energy Engineering, Universitat Politècnica de València, Camí de Vera, s/n, 46022 València, Spain
3Research Institute for Industrial, Radiophysical and Environmental Safety, Universitat Politècnica de València, Camí de Vera, s/n, 46022 València, Spain

Correspondence should be addressed to S. Chiva; se.iju.cme@avihcs

Received 27 July 2017; Accepted 6 December 2017; Published 16 January 2018

Academic Editor: Tomasz Kozlowski

Copyright © 2018 C. Peña-Monferrer et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The one-dimensional two-fluid model approach has been traditionally used in thermal-hydraulics codes for the analysis of transients and accidents in water–cooled nuclear power plants. This paper investigates the performance of RELAP5/MOD3 predicting vertical upward bubbly flow at low velocity conditions. For bubbly flow and vertical pipes, this code applies the drift-velocity approach, showing important discrepancies with the experiments compared. Then, we use a classical formulation of the drag coefficient approach to evaluate the performance of both approaches. This is based on the critical Weber criteria and includes several assumptions for the calculation of the interfacial area and bubble size that are evaluated in this work. A more accurate drag coefficient approach is proposed and implemented in RELAP5/MOD3. Instead of using the Weber criteria, the bubble size distribution is directly considered. This allows the calculation of the interfacial area directly from the definition of Sauter mean diameter of a distribution. The results show that only the proposed approach was able to predict all the flow characteristics, in particular the bubble size and interfacial area concentration. Finally, the computational results are analyzed and validated with cross-section area average measurements of void fraction, dispersed phase velocity, bubble size, and interfacial area concentration.