NUMERICAL MODELING OF FLOW AND MASS TRANSFER EFFECT ON FLOW-ACCELERATED CORROSION IN CONSECUTIVE ELBOWS

Abstract

Elbows are the most common fittings in piping systems of nuclear power plants, and can experience enhanced flow-accelerated corrosion (FAC) thinning rates in comparison to the straight pipe. When 2 elbows are in close proximity, the flow through the upstream elbow may influence the mass transfer and FAC thinning rate in the downstream elbow. Therefore, the flow condition and the corresponding mass transfer coefficient (MTC) determine the local distribution of FAC wall thinning in the elbows. This paper presents the numerical analysis of the MTC (in nondimensional form, Sherwood number) and its enhancement factor in small-bore piping (1″ inner diameter) under single-phase flow conditions, for 3 arrangements of 2 consecutive elbows: (i) in-plane S-configuration, (ii) in-plane C-configuration, and (iii) out-of-plane configuration. The commercial computational fluid dynamics tool ANSYS FLUENT® is used to simulate the flow and mass transfer for the various elbow configurations. The numerical results for the MTC enhancement factors for the 3 piping configurations agree with the experimental results. To apply these small-bore results to large-bore operating conditions found in nuclear power plants, the effect of Reynolds number is also considered. The results show that the MTC enhancement factors of the downstream elbow, affected by the upstream flow, is higher than that of the upstream elbow for all 3 consecutive elbow configurations.