Modeling and prediction of interfacial area transport in two-phase flow within a tight lattice bundle

Abstract

The interfacial area concentration (IAC) is the two-fluid model’s key parameter, determining the interfacial transfer terms’ constitutive relations. To dynamically forecast IAC developments, the interfacial area transport equation (IATE) has been proposed. Tight lattice fuel assemblies with P/D < 1.1 are extensively utilized in the conceptual designs of small modular reactors. To investigate the interface transport characteristics and develop the IATE for the tight lattice fuel assembly, we established a two-phase flow parameter database for a tight lattice rod bundle with P/D = 1.06, covering void fraction, bubble velocity, bubble size distribution (BSD), and IAC. The BSD and IAC data were obtained using an in-house developed wire-mesh sensor (WMS) combined with a new post-processing method, known as the Eulerian post-processing method. This paper utilized the IAC data in the tight lattice bundle channel to benchmark the classical IATE models, including the Fu, Sun, and Yang models. Results indicate the Fu model most accurately predictes the development of IAC in the current channel. For the one-group (G₁) flow, the Fu model’s average and maximum relative deviations are 5.1 % and 14.3 %, respectively. Meanwhile, for the two-group (G₂) flow, the Fu model’s average and maximum relative deviations are 12.1 % and 25.6 %, respectively. Based on the Fu model, combined with the G₂ bubbles’ characteristics in the tight lattice bundle, this paper proposes an optimized IATE model by correcting the G₂ bubble base shearing-off perimeter and shape factor. The optimized model suppresses the contribution of the shearing-off term and greatly improves the prediction accuracy of the two-group IAC evolution inside the current bundle channel. For the two-group flow, the new model’s average and maximum relative deviations of IAC are 6.56 % and 14.9 %, respectively. However, calculation results also show that the IATE may not predict the IAC and void fraction transport synchronously in some cases, due to the assumption of a flat bubble number density distribution. Hence, in future studies, the IATE considering BSD evolution information is recommended to be developed to further enhance the model accuracy.