Void fractions in a rod bundle geometry at high pressure–part Ⅰ: Experimental study

Abstract

An investigation of void fraction measurement and prediction in a triangular-array rod bundle geometry was carried out under high pressure conditions (P = 5–9 MPa and G = 100–350 kg·m−2·s−1). The aims of this work were to expand the existing database and assess and modify the predictive models. The present paper is the Part I of this study, where the experimental work was presented to measure local, chordal and area-average void fractions respectively by a comprehensive measuring system composed by optical probes and gamma-ray densitometry. Non-uniform distribution of void fraction was investigated by local-to-local and local-to-average comparisons of void fractions. The results indicated that non-uniform distribution was not only related to the geometry, but also affected by the transition of flow regimes in rod bundle. The effects of pressure and mass flux on void fractions were also analyzed in detail in consideration of variations of fluid properties and drift-flux parameters. Additionally, both void fraction and interface frequency were compared with the flow regime map in TRACE code. The variation of interface frequency indicated that the droplet entrainment would occur in annular flow at high mass flux. In the Part Ⅱ of this study, an assessment of existing models for void fraction prediction in rod bundles was carried out according to the present data and a newly-developed drift-flux model was proposed.